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Etiology and evaluation of the child with weakness

Etiology and evaluation of the child with weakness
Literature review current through: Jan 2024.
This topic last updated: May 23, 2023.

INTRODUCTION — The approach to the child with weakness will be reviewed here. The approach to an infant or newborn with hypotonia or weakness is discussed separately. (See "Approach to the infant with hypotonia and weakness" and "Overview of peripheral nerve and muscle disorders causing hypotonia in the newborn".)

DEFINITIONS — Weakness is a decreased ability to voluntarily and actively move muscles against resistance. Weakness may arise from any portion of the motor unit and is typically divided into upper motor neuron and lower motor neuron weakness as follows:

Upper motor neuron weakness – Upper motor neuron weakness arises from lesions in the cerebral cortex and corticospinal tracts down to, but not including, the anterior horn cell in the ventral spinal cord.

Lower motor neuron weakness – Lower motor neuron weakness results from lesions located in the anterior horn cell, peripheral nerve, neuromuscular junction, or muscle.

Weakness can be confused with hypotonia or ataxia. Hypotonia is a decreased resistance to passive range of motion. Ataxia refers to decreased muscular coordination. (See "Approach to the infant with hypotonia and weakness" and "Approach to the child with acute ataxia".)

CAUSES OF ACUTE WEAKNESS — The causes of acute weakness are provided in the table (table 1). Many of the conditions that cause acute muscle weakness are potentially life-threatening. Mortality due to acute muscle weakness is typically caused by respiratory failure or by lesions in the brain that cause both weakness and increased intracranial pressure.

Upper motor neuron lesion — Patients with acute upper motor neuron lesions may initially present with altered mental status and focal neurologic findings such as unequal pupils, visual field defects, cranial nerve palsies, and/or paralysis on the opposite side of the central nervous system lesion. During the acute phase, upper motor neuron lesions are associated with decreased spinal cord reflexes and hypotonia. Over the period of several weeks, spasticity, hyperreflexia, and "upper motor neuron" signs (eg, positive Babinski sign) develop.

In pediatric patients, it is important to emphasize that classic distal upper motor neuron findings are often not present during the early phases of illness.

Cerebral cortex

Intracranial hemorrhage — Traumatic epidural or subdural hematoma occurs in children who have sustained severe head trauma (Glasgow Coma Scale <9 (table 2)) but may also be present in pediatric patients who are less symptomatic, especially in infants with open fontanelles in whom intracranial pressure may increase more gradually. In addition to altered mental status, patients often display findings of increased intracranial pressure (eg, vomiting, tachycardia or bradycardia, increased blood pressure, and focal neurologic signs). The diagnosis of intracranial hemorrhage usually includes demonstration of intracranial hemorrhage on neuroimaging. The presence of intracranial hemorrhage without a clear history of trauma is suggestive of abusive head trauma, an underlying bleeding disorder, or acute stroke. The approach to pediatric patients with severe head trauma, subdural hematoma, and epidural hematoma are discussed separately. (See "Severe traumatic brain injury (TBI) in children: Initial evaluation and management" and "Intracranial epidural hematoma in children" and "Intracranial subdural hematoma in children: Clinical features, evaluation, and management".)

Less commonly, rupture of a preexisting arteriovenous malformation or aneurysm may cause subarachnoid hemorrhage. Most of these patients are asymptomatic prior to rupture. These children present with severe headache which is often associated with sudden weakness and altered mental status. (See "Aneurysmal subarachnoid hemorrhage: Treatment and prognosis".)

Stroke — Stroke is a rare cause of weakness in children. Infants with stroke may present with focal weakness, but are more likely than older children to present with seizures and altered mental status. Older children usually have hemiparesis or other focal neurologic signs such as aphasia, visual disturbance, or cerebellar signs, although seizures, headache, and lethargy are not uncommon. Neck pain can be associated with cervical artery dissection, and a Horner's syndrome may accompany carotid dissection. Neuroimaging confirms the diagnosis. Common preexisting medical issues contributing to stroke in children and adolescents include sickle cell disease and structural cardiac abnormalities.

The etiology, clinical features and management of stroke in children is discussed separately. (See "Ischemic stroke in children and young adults: Epidemiology, etiology, and risk factors" and "Ischemic stroke in children: Clinical presentation, evaluation, and diagnosis".)

Brain tumor — Intracranial tumors, either malignant or benign, may cause weakness in addition to many other clinical findings that vary according to whether the fontanelles are closed and the location of the tumor. Intracranial tumors can present with or be exacerbated by hemorrhage into the tumor. These patients usually either have a history of known brain tumor or a history of clumsiness, weakness, behavioral changes, and vomiting. When the acute hemorrhage occurs, symptoms include weakness, severe headache, and vomiting. (See "Clinical manifestations and diagnosis of central nervous system tumors in children", section on 'Clinical manifestations'.)

Seizure — Todd paralysis is a temporary focal weakness (eg, hemiparesis) following a seizure. It generally improves rapidly during the postictal period with resolution in minutes to hours. (See "Seizures and epilepsy in children: Clinical and laboratory diagnosis", section on 'Behavior after the event'.)

Hemiplegic migraine — A typical migrainous aura is characterized by progressive neurologic deficits or disturbances with subsequent complete recovery. Visual disturbances are the most common type of aura. However, auras may also involve other senses or occasionally cause motor or speech deficits. (See "Types of migraine and related syndromes in children", section on 'Migraine with aura'.)

Hemiplegic migraine is manifested by motor and sensory symptoms that are unilateral. These symptoms can last longer than the headache itself. Complete recovery may take weeks in some cases; permanent weakness can occur after multiple attacks. Hemiplegic migraine is divided into familial and sporadic subtypes. Familial hemiplegic migraine is an uncommon autosomal dominant disorder linked to specific gene mutations. In addition, there are some patients who are the first member of their family to have hemiplegic migraine. They are referred to as having spontaneous hemiplegic migraine and may or may not carry one of the described gene variants. (See "Hemiplegic migraine".)

Alternating hemiplegia of childhood — This very rare condition is characterized by periodic episodes of hemiplegia or quadriplegia beginning in infancy [1]. Other findings include paroxysmal eye movements (eg, nystagmus), seizures, cognitive impairment, and ataxia. Episodes often improve or resolve after sleep. A family history of migraine may also be present. The diagnosis is made based upon the clinical findings and excluding brain abnormalities by neuroimaging. These patients warrant prompt referral to a pediatric neurologist.

Spinal cord

Spinal cord trauma — Traumatic injuries may damage the spinal cord, either transiently or permanently. The cervical spine is the most frequent site of injury. Clinical features vary according to the degree of cord injury and the level of the injury. Patients may demonstrate spinal shock with bradycardia and hypotension. Associated brain and systemic injuries (eg, hemothorax, extremity fractures, and intraabdominal injury) are common. The initial stabilization, evaluation, and treatment are discussed separately. (See "Acute traumatic spinal cord injury" and "Evaluation and acute management of cervical spine injuries in children and adolescents".)

Spinal cord concussion may occur after a direct blow to the head, neck, or back and presents with impairment of sensory and motor function below the level of the injury. Patients with this injury generally recover, often within hours. Other traumatic injuries include spinal epidural hematoma, vertebral column fractures or dislocations, and spinal cord injury without radiographic abnormality (SCIWORA). (See "Spinal cord injury without radiographic abnormality (SCIWORA) in children".)

Spinal cord tumor — Focal weakness and peripheral or back pain are the most common presenting symptoms of a spinal cord tumor. Incontinence may also occur. Neuroimaging, typically magnetic resonance imaging for the appropriate spinal level establishes the diagnosis. (See "Clinical manifestations and diagnosis of central nervous system tumors in children".)

Paraspinal infection or inflammation — Epidural abscess and discitis are rare causes of weakness in children. Children with epidural abscess may display the classic diagnostic triad of fever, spinal pain, and neurologic deficits, but only a few patients have all three components at presentation. Over time, an untreated epidural abscess is associated with a typical progression of symptoms from back pain (often focal and severe), to root pain (described as "shooting" or "electric shocks"), to neurologic deficits (motor weakness, sensory changes, and bowel and bladder dysfunction), and finally paralysis, which may quickly become irreversible. (See "Spinal epidural abscess", section on 'Clinical manifestations'.)

Discitis refers to inflammation of the intervertebral disc. Most patients with discitis are under three years of age and complain of back pain, with or without fever, but rarely, the infection may spread to the epidural space and cause weakness. The etiology is controversial. The current consensus, backed by scant supportive evidence, is that discitis in children usually represents low-grade infection and is on one end of the spectrum of vertebral osteomyelitis. Although disc biopsy is not necessary for diagnosis, when it is performed, as many as 60 percent of tissue samples grow bacteria, usually Staphylococcus aureus. However, children often recover without antibiotic therapy. (See "Back pain in children and adolescents: Causes", section on 'Discitis'.)

Transverse myelitis — Transverse myelitis is an inflammatory condition of unclear etiology. Symptoms are characterized by motor and sensory deficits attributable to myelin destruction in one or both sides of the spinal cord. They include pain, weakness, paresthesias, and sphincter dysfunction. These typically present over a few days, with paresthesias preceding the weakness and urinary retention. A hyperacute presentation sometimes occurs with a rapid onset of paraplegia, sensory abnormalities, and urinary retention. This form is often associated with significant back pain. A discrete sensory level may or may not be detected with either presentation. A thoracic sensory level is frequently found in children. Diagnosis is made based upon clinical criteria and is confirmed by characteristic findings of transverse myelitis on magnetic resonance imaging. The clinical features and diagnosis of transverse myelitis is discussed in greater detail separately. (See "Transverse myelitis: Etiology, clinical features, and diagnosis", section on 'Clinical features' and "Transverse myelitis: Etiology, clinical features, and diagnosis", section on 'Initial evaluation'.)

Lower motor neuron lesion — Patients with lower motor neuron weakness typically display muscle weakness, hypotonia, fasciculations, and decreased spinal cord reflexes. Mental status is typically, but not always preserved depending upon the cause and whether respiratory failure has occurred.

Anterior horn cell disease

Poliomyelitis and other enteroviruses — Although polio no longer poses the public health threat in the United States and other developed countries that it once did, areas of endemic wild-type poliovirus still exist in other parts of the world. Poliovirus is a species of human enterovirus. A small fraction of patients with poliovirus infection develop central nervous system (CNS) infection. After invading the CNS, the virus uncoats, viral replication occurs, and the motor neuron dies, leading to paralysis of muscle fibers supplied by this motor neuron. Weakness may vary from one muscle or group of muscles, to quadriplegia, and respiratory failure. Tone is reduced, nearly always in an asymmetric manner. Proximal muscles usually are affected more than distal ones, and legs more commonly than arms. Reflexes are decreased or absent. The sensory examination is normal. (See "Poliomyelitis and post-polio syndrome", section on 'Poliomyelitis'.)

Sporadic cases of acute paralysis similar to paralytic poliomyelitis also occur with other enterovirus serotypes, the most important of which is enterovirus A71. Large outbreaks of paralytic disease associated with enterovirus A71 involving hundreds of cases, mostly in children less than six years old have been reported from eastern Europe and Russia, and more recently in Taiwan, Thailand, and China. Enterovirus A71 is associated with hand-foot-mouth disease in most cases. Some children have presented with brainstem encephalitis, non-cardiogenic pulmonary edema, and a rapidly fatal course.

Acute flaccid myelitis (AFM) is a rare but serious pattern of symptoms that causes limb weakness, mostly in children, and has been associated with enterovirus D68 (EV-D68) infection. Most patients develop symptoms in the late summer or early fall in the United States. Characteristic features of this disorder are a febrile or respiratory illness before the onset of neurologic symptoms and a presentation similar to poliomyelitis, with limb weakness, variable cranial nerve involvement (eg, facial weakness, ophthalmoplegia, dysarthria, or dysphagia), and magnetic resonance imaging (MRI) evidence of gray matter involvement in the spinal cord. The combination of hypotonic weakness and radiographic or electrophysiologic evidence of anterior horn cell involvement are the most specific findings in AFM. (See "Acute flaccid myelitis".)

Peripheral nerve

Guillain-Barré syndrome — In children, Guillain-Barré syndrome (GBS) most commonly presents with an acute, progressive, symmetric, ascending weakness over hours to days. Less commonly, patients can present with primarily sensory dysfunction or ophthalmoplegia, ataxia and bulbar dysfunction (Miller-Fisher Syndrome). If weakness progresses, respiratory failure requiring mechanical ventilation may occur. (See "Guillain-Barré syndrome in children: Epidemiology, clinical features, and diagnosis" and "Guillain-Barré syndrome in children: Treatment and prognosis".)

Peripheral nerve toxins — Toxins that can cause life-threatening weakness include heavy metals (eg, arsenic, mercury, thallium), ciguatera fish poisoning (ciguatoxin), and paralytic shellfish poisoning (saxitoxin). (See "Ciguatera fish poisoning" and "Overview of shellfish, pufferfish, and other marine toxin poisoning", section on 'Paralytic shellfish poisoning' and "Overview of acquired peripheral neuropathies in children", section on 'Toxins'.)

Acute intermittent porphyria — Acute intermittent porphyria (AIP) is both the most common and most severe of the inherited porphyrias. It is an autosomal dominant disorder resulting from a partial deficiency of porphobilinogen deaminase (PBGD) activity, the third enzyme in the pathway of heme synthesis. The neuropathic symptoms most commonly involve muscle weakness with more involvement of proximal muscle groups. Symptoms generally begin after puberty and may be triggered by stress, decreased food intake, a number of different medications (eg, barbiturates, sulfonamides, estrogen, griseofulvin) (table 3), and, in women, menses. (See "Acute intermittent porphyria: Pathogenesis, clinical features, and diagnosis".)

Other — Many other conditions may cause peripheral neuropathy with varying degrees of weakness. (See "Overview of acquired peripheral neuropathies in children".)

Neuromuscular junction disorders — Diseases of the neuromuscular junction affect strength but usually leave sensory function intact.

Botulism — Botulism is caused by a neurotoxin that blocks the release of acetylcholine at the neuromuscular junction. The toxin is produced by the Clostridium botulinum bacterium, a soil-dwelling, gram-positive anaerobe. There are three main presentations of botulism: foodborne, wound-associated, and most commonly, infant botulism. Classic, or foodborne botulism, is caused by eating food contaminated by clostridial toxin. Symptoms include vision changes, difficulty swallowing, and, ultimately, progressive weakness. Wound botulism presents similarly to classic botulism but the toxin arises from a grossly infected wound. In infant botulism, the bacteria are ingested and produce toxin within the child's gastrointestinal tract. Infants with botulism present with constipation, lethargy, and poor tone. Honey, which can be contaminated with C botulinum spores, has been associated with infant botulism. Most cases of infant botulism in the United States are thought to result from exposure to dust containing C. botulinum spores from construction sites or agricultural areas. Infant botulism, although rare, is one of the most common causes of acute, generalized weakness in infants. (See "Neuromuscular junction disorders in newborns and infants", section on 'Infant botulism'.)

Myasthenia gravis — Myasthenia gravis is an antibody-mediated autoimmune disease that affects the postsynaptic neuromuscular junction. Most commonly, it presents in a slowly progressive fashion. However, myasthenic crises can occur, which can lead to respiratory failure. The most common symptoms of myasthenia gravis include ptosis and diplopia. These symptoms are generally exacerbated by activity and relieved by rest. Transient neonatal myasthenia affects 10 to 15 percent of babies born to mothers with myasthenia gravis. It can lead to weakness, dysphagia, and occasionally, respiratory distress or failure. (See "Clinical manifestations of myasthenia gravis" and "Myasthenic crisis" and "Neuromuscular junction disorders in newborns and infants".)

The ice pack test or, where available, edrophonium test are bedside methods that support the diagnosis of myasthenia gravis. However, these tests are associated with false-positive results, thus consultation with a pediatric neurologist is indicated to guide confirmation by serologic tests and electrophysiologic studies. (See "Diagnosis of myasthenia gravis".)

Organophosphate or carbamate poisoning — Organophosphates and carbamates are potent cholinesterase inhibitors capable of causing severe cholinergic toxicity with weakness and paralysis following cutaneous exposure, inhalation, or ingestion (figure 1). Although structurally distinct, the clinical manifestations and management of organophosphate and carbamate toxicity are similar. A rapid overview provides clinical features and emergent management of organophosphate and carbamate toxicity (table 4). (See "Organophosphate and carbamate poisoning".)

Neurotoxic snake envenomation — Venoms of many elapids and some vipers (eg, cobra, coral snake, water snake, or Russell’s) are associated with severe descending neurotoxicity. Neurotoxicity is characterized initially by ptosis, diplopia, and bulbar palsy with onset between 1 to 10 hours following envenomation. Symptoms can later progress to dysarthria and more generalized weakness. As a result, frequent, serial observations for ptosis, diplopia, and impaired swallowing function are of paramount importance. Ventilatory support may be required for airway protection or respiratory paralysis. (See "Snakebites worldwide: Clinical manifestations and diagnosis", section on 'Geographic distribution and characteristics'.)

Tick paralysis — Tick paralysis is a rare form of weakness caused by toxin excreted during feeding by female ticks, primarily from the Dermacentor and Ixodes genus.

Tick paralysis caused by Dermacentor ticks usually begins with paresthesias and a sense of fatigue and weakness, although individual patients may sometimes appear irritable or restless and complain of muscular pain. Fever is characteristically absent, and there is no change in the sensorium or headache unless severe hypoxia or hypercarbia are present. Most patients eventually develop an unsteady gait that progresses to an ascending complete paralysis. Deep tendon reflexes are characteristically absent. Respiratory paralysis and death can occur in severe cases. (See "Tick paralysis".)

Muscle

Rhabdomyolysis — Injury can lead to breakdown of skeletal muscle tissue, causing the release of creatinine kinase and other intracellular substances. The classic symptom triad includes myalgias, weakness, and dark urine. Rhabdomyolysis in children most commonly occurs as a result of viral myositis. Other causes include trauma, connective tissue disease, toxins, and exercise. (See "Rhabdomyolysis: Clinical manifestations and diagnosis".)

Myositis — Myositis may occur in the setting of systemic viral or bacterial infection. Viral myositis is a common pediatric condition that is usually self-limited. However, in its most severe and rare form, it can cause severe weakness with rhabdomyolysis. Although many viruses can cause myositis, it is most commonly due to infection with influenza (benign acute childhood myositis), which rarely progresses to rhabdomyolysis. This condition is characterized by refusal to walk with marked tenderness of bilateral calf muscles and pain on passive or active dorsiflexion of the feet in a child who is in the recovery phase of influenza. (See "Overview of viral myositis", section on 'Benign acute childhood myositis'.)

The course of acute viral myositis complicated by massive rhabdomyolysis is highly variable and relates to the course of the complications of rhabdomyolysis, including renal failure, fluid and electrolyte abnormalities, and cardiac arrhythmias. Other complications that can occur include respiratory failure secondary to respiratory muscle necrosis and weakness, infection, and pulmonary embolus. In most cases, with prompt recognition and appropriate directed therapy, muscle strength and renal function recover fully, usually within one to two weeks of the onset of rhabdomyolysis. (See "Overview of viral myositis", section on 'Benign acute childhood myositis'.)

Pyomyositis is a purulent infection of skeletal muscle that arises from hematogenous spread, usually with abscess formation. In healthy children, it is most commonly seen in tropical regions. Patients with pyomyositis in temperate zones more frequently are immunocompromised.

Pyomyositis presents with fever and pain with cramping localized to a single muscle group. The disease occurs most often in the lower extremity (sites include the thigh, calf and gluteal muscles), but any muscle group can be involved, including the iliopsoas, pelvic, trunk, paraspinal, and upper extremity muscles. Multifocal infection with involvement of more than one muscle group may be observed in up to 20 percent of cases. (See "Primary pyomyositis".)

Familial periodic paralysis — The abrupt onset of weakness in association with high, low, or normal serum potassium values is a rare form of familial paralysis that is inherited in an autosomal dominant fashion. (See "Hypokalemic periodic paralysis" and "Hyperkalemic periodic paralysis".)

Trichinellosis — Trichinellosis is caused by the ingestion of nematode cysts of the parasite Trichinella during the consumption of undercooked meat (eg, pork, wild bear). Approximately one week after eating the tainted meat, larvae enter skeletal muscles causing muscle pain, tenderness, swelling, and weakness. The pain can be so extreme as to limit all movement, including breathing or moving the tongue. High fever lasting a number of weeks is often seen and laboratory evaluation often reveals a marked eosinophilia. (See "Trichinellosis".)

Other

Electrolyte disturbance — Muscle weakness may indicate underlying hypokalemia, hypophosphatemia, hypocalcemia, hyponatremia, or hypernatremia.

Drug-related — Many medications (eg, isoniazid, nitrofurantoin, zidovudine, magnesium sulfate, and several chemotherapeutic agents) can cause weakness due to adverse effects on function of the peripheral nerve, neuromuscular junction, or muscle (table 5). In addition, chronic inhalant drug abuse with toluene containing agents, ingestion of sedative-hypnotics, muscle relaxants (eg, cyclobenzaprine), opioids, or drugs that can cause rhabdomyolysis (eg, amphetamines, phencyclidine) may cause significant muscle weakness.

Conversion disorder — Conversion disorder (functional neurologic symptom disorder) is defined as a symptom or deficit in voluntary motor function in patients without an anatomic or physiologic basis. In children, conversion disorder occurs more commonly in girls than boys and is most prevalent in children between the age of 10 to 15 years [2,3]. Risk factors include prior sexual abuse and preexisting psychiatric disease (eg, anxiety, depression). In children, symptoms are most commonly related to motor function and often start after an emotional stress or minor injury.

In most cases, a detailed history identifies domestic stress (eg, parental divorce), feelings of parental rejection, unresolved grief, and/or problems at school (eg, bullying, recent failure) [2].

Physical examination often provides early diagnosis without extensive laboratory evaluation or ancillary studies. Key findings include reciprocal contraction during attempts to move apparently paralyzed muscle groups (ie, contraction of both agonist and antagonist muscles such as the biceps and triceps during strength training), presence of normal tendon reflexes in flaccid extremities, give-way weakness, or physically implausible presentations (eg, triparesis). (See "Functional neurological symptom disorder (conversion disorder) in adults: Clinical features, assessment, and comorbidity", section on 'Weakness and paralysis'.)

Successful treatment involves early referral for psychiatric care and avoidance of extensive investigation for an organic cause.

CAUSES OF CHRONIC WEAKNESS — Many causes of chronic muscle weakness in children arise from congenital disorders that are apparent shortly after birth or in early childhood (table 6). These include Erb palsy, congenital neuropathies, anterior horn cell disorders (eg, spinal muscular atrophy), congenital myopathies, muscular dystrophy, and inborn errors of metabolism. (See "Overview of peripheral nerve and muscle disorders causing hypotonia in the newborn".)

Abnormalities of the central nervous system, such as cerebral palsy or myelomeningocele (spina bifida), also result in chronic weakness or paralysis. (See "Cerebral palsy: Classification and clinical features" and "Myelomeningocele (spina bifida): Management and outcome".)

Progressive subacute muscle weakness may be seen in children with an expanding brain tumor, Chiari malformation, tethered cord, dermatomyositis, prolonged heavy metal exposure (eg, arsenic), or neurodegenerative diseases (eg, metachromatic leukodystrophy, Alexander disease, Krabbe disease, and juvenile amyotrophic lateral sclerosis). (See appropriate topic reviews.)

Congenital hypothyroidism remains an important cause of muscle weakness in infants in many parts of the world. The Kocher-Debre-Semelaigne syndrome describes infants with typical features of cretinism associated with diffuse muscular hypertrophy and muscle weakness that is predominantly proximal. These infants have motor and cognitive developmental delay, constipation, myxedema, enlarged tongue, and coarse hair and skin typical of cretinism. Despite a very muscular, almost muscle-bound appearance, they are in fact weak and often have difficulty with sitting and head control. Where implemented, neonatal screening has markedly reduced the number of infants with florid hypothyroidism. (See "Hypothyroid myopathy", section on 'Congenital hypothyroidism' and "Clinical features and detection of congenital hypothyroidism".)

Cushing's syndrome is another important and potentially reversible endocrine cause of chronic muscle weakness. In children, Cushing's syndrome most commonly arises from exogenous steroid administration and is frequently accompanied by striae, centripetal obesity, a "buffalo hump", steroid acne, and hypertension. (See "Epidemiology and clinical manifestations of Cushing syndrome".)

Chronic weakness may also rarely occur as a manifestation of a conversion disorder.

EVALUATION

Initial stabilization — In a child presenting with weakness, the clinician should first focus on the child's airway, breathing, and circulation. Many causes of weakness may lead to respiratory insufficiency and failure. Thus, the clinician should carefully assess respiratory effort, air movement, and pulse oximetry. (See "Initial assessment and stabilization of children with respiratory or circulatory compromise".)

The presence of Cushing's triad (bradycardia, hypertension, and irregular respirations) or altered mental status should prompt emergent evaluation for and treatment of increased intracranial pressure. (See "Elevated intracranial pressure (ICP) in children: Management", section on 'Initial stabilization' and "Elevated intracranial pressure (ICP) in children: Management", section on 'Ongoing Management' and "Elevated intracranial pressure (ICP) in children: Management", section on 'Treatment of elevated ICP'.)

History — Several historical features help differentiate the cause of weakness in children:

Timing – Sudden, severe deterioration without trauma suggests subarachnoid hemorrhage, stroke, or brain tumor with hemorrhage. Subacute, chronic, or indolent presentations are more suggestive of transverse myelitis, neuropathies (eg, Guillain-Barré syndrome) or myopathies (eg, muscular dystrophy). Weakness that worsens over the course of the day or preferentially affects the extraocular muscles is consistent with myasthenia gravis.

Trauma – Weakness following trauma increases the concern for intracranial hemorrhage (eg, epidural hematoma) or spinal cord injury. Weakness immediately after birth would be concerning for nerve injury associated with childbirth (eg, Erb palsy).

Seizure – Weakness in association with a seizure may indicate acute intracranial hemorrhage or stroke but may also be caused by a self-limited Todd paralysis. Often, the child has a prior history of seizures with Todd paralysis. In addition, Todd paralysis should resolve within a few hours of the seizure.

Headache – Headache and weakness, especially in children with progressive morning vomiting or focal neurological signs, is highly suggestive of an intracranial mass lesion. Children with an intracranial hemorrhage or stroke may also experience rapid onset of a severe headache, often described as the worst of their life. Weakness that is followed by a migrainoid headache is seen in children with hemisyndrome migraine.

Neck or back pain – Patients with Guillain-Barré syndrome, poliomyelitis, transverse myelitis, epidural spinal hematoma, or epidural spinal abscess often complain of neck or back pain.

Fever – Fever is seen in patients with viral myositis, pyomyositis, and trichinellosis. In addition, a febrile illness may be a triggering stress in patients with acute intermittent porphyria.

Exercise-induced – Weakness associated with exercise is characteristic of patients with myasthenia gravis, periodic paralysis, rhabdomyolysis, and myotonic dystrophy.

Diet – Reef fish ingestion may lead to ciguatera poisoning. Paralytic shellfish poisoning occurs in patients who eat shellfish harvested from contaminated beds or during times of algae blooms known as red tides. Trichinellosis occurs in patients who consume undercooked pork or other contaminated meat (eg, wild bear meat). Outbreaks of food borne botulism usually involve consumption of home canned foods such as fruits, vegetables, and fish.

Constipation – In infants, a history of constipation and poor feeding with generalized weakness suggests infant botulism.

Dark urine – A history of dark red or brown urine should prompt consideration of rhabdomyolysis. Pigmenturia will be missed in rhabdomyolysis if the filtered load of myoglobin is insufficient or has largely resolved before the patient seeks medical attention.

Medications and toxins – The clinician should identify any potential exposures to heavy metals (eg, arsenic, mercury, thallium), organophosphates, or medications known to cause weakness, such as corticosteroids (table 5).

Physical examination — The patient should undergo a complete physical examination with specific attention to muscle and neurologic findings.

Muscle examination — When evaluating a patient complaining of muscle weakness, the examiner should follow a systematic approach that includes inspection of muscle, palpation and percussion of muscle, assessment of tone and manual muscle strength testing, and assessment of motor function. Joint examination and neurologic examination, including testing of the deep tendon reflexes and sensory testing, are important adjuncts to the muscle examination. Evaluation of muscle weakness in the adult is discussed separately. (See "Muscle examination in the evaluation of weakness".)

Inspection – Muscle atrophy indicates chronic muscle disuse or denervation. Hypertrophy occurs in patients with Becker and Duchenne muscular dystrophy. Fasciculations suggest a lower motor neuron disorder (eg, spinal muscular atrophy). Ptosis is found in children with myasthenia gravis, botulism, and neurotoxic snake envenomation.

Palpation and percussion – Muscle tenderness occurs in patients with myopathic weakness including those with myositis, trichinellosis, and rhabdomyolysis. Focal tenderness over the spine may be seen with epidural abscess or transverse myelitis.

Tone and muscle strength testing in the infant – Tone is defined as the patient's passive resistance to movement. Tone in infants can be assessed by observing resistance of the upper or lower extremity as it is pulled by the examiner or by the pull-to-sit maneuver, in which the infant's hands are grasped and the baby is pulled from a supine to sitting position. The normal infant will offer some resistance, with flexion at the knees, elbows, and ankles. The head should move with the body and head lag should be minimal. Pronounced head lag may indicate hypotonia.

Muscle strength also can be tested by holding the infant in a vertical position with the feet on a flat surface. A normal infant should be able to bear weight on the lower extremities while attempting to stand. In addition, infants with normal tone hold the wrist or ankle in line with the rest of the extremity. Strength is measured by examining the patient's active movement.

Manual muscle strength testing in the older child – The Medical Research Council's grading system for muscle strength is widely used. The examiner assesses the patient's ability to move the muscle against resistance provided by the examiner who, through experience, has developed a sense of the expected range of normal motor function. This will vary from patient to patient depending upon the age of the subject (table 7).

Decreased effort because of pain, fatigue, or malingering may be identified by "give" weakness in which there is initially a full effort followed by the abrupt loss of strength against resistance; this type of response does not occur in the truly weak individual. If intentionally decreased cooperation is suspected, observing the patient performing simple functional tasks such as sitting up from a supine position or toe or heel walking may reveal a discrepancy compared with the patient's performance on directed muscle strength testing.

Muscle weakness patterns – The pattern of muscle weakness helps identify the underlying pathophysiology:

Generalized weakness is found in patients with myasthenia gravis, periodic paralysis, and organophosphate or carbamate poisoning, although some children with myasthenia gravis will have only ptosis or weakness confined to the cranial nerves.

Asymmetric weakness (paraplegia or hemiplegia) is seen in patients with intracranial tumor or hemorrhage, stroke, hemisyndrome migraine, spinal cord lesions, acute flaccid myelitis (AFM), and Todd paralysis.

Symmetric weakness may be subdivided into proximal, distal, or regional weakness:

-Proximal weakness is characteristic for muscle disorders such as rhabdomyolysis, viral myositis, congenital myopathies, Duchenne muscular dystrophy, dermatomyositis, acute intermittent porphyria, and anterior cord syndrome following trauma or spinal vascular injury.

-Distal weakness suggests peripheral neuropathy (eg, Guillain-Barré syndrome) or motor neuron disease, such as spinal motor atrophy or the congenital motor neuropathies (eg, juvenile amyotrophic lateral sclerosis).

-Regional weakness may be found adjacent to the feeding female tick in patients with tick paralysis.

Neurologic examination — In addition to motor function, children with muscle weakness warrant a complete neurologic assessment. (See "Detailed neurologic assessment of infants and children".)

It is important to differentiate between muscle weakness and ataxia. The difference is particularly difficult to discern when the presenting complaint is "altered gait" or "can't sit up" in an infant. In general, when movement abnormalities are due to weakness, they will be present regardless of patient position, type of movement or task. Although the differential diagnosis of ataxia and muscle weakness overlap, the approach may differ [4]. (See "Approach to the child with acute ataxia".)

Findings of particular importance include the following:

Ophthalmoplegia and other cranial nerve deficits are seen in patients with neuromuscular junction disorders such as botulism, myasthenia gravis, neurotoxic snake envenomation, and tick paralysis. They may also be seen in the Miller-Fisher variant of Guillain-Barré syndrome.

Patients with spinal cord disorders have loss of sensation below the level of the lesion and may have decreased rectal tone and, in boys, decreased or absent cremasteric reflexes.

Sensory abnormalities, including neurogenic pain, are suggestive of peripheral nerve and spinal cord disorders.

Unusual sensations, such as hot-cold temperature reversal, in association with a feeling that the teeth are loose, are found in patients with ciguatera poisoning.

Sensation is intact in patients with neuromuscular junction disorders (eg, botulism, myasthenia gravis) and muscle disease (eg, congenital myopathy, muscular dystrophy, dermatomyositis).

Cerebellar abnormalities (eg, ataxia, dysmetria, ulnar drift) suggest a central nervous system lesion.

Deep tendon reflexes are typically diminished or absent in patients with Guillain-Barré syndrome, botulism, spinal muscular atrophy, or tick paralysis. They are increased in patients with upper motor neuron lesions that are not acute.

Other findings — The patient's skin should be searched for an engorged tick, especially in the scalp, at the hairline, and in gluteal fold.

Skin findings of dermatomyositis include Gottron papules on the hands, facial heliotrope rash (picture 1), periungual capillary changes, and dystrophic calcification (picture 2).

Ancillary studies — Emergent ancillary studies in the weak child focus on assessment of respiratory status and identification of etiologies amenable to medical or surgical treatment.

Assessment of respiratory function – Blood gas assessment, ancillary respiratory assessment tools (eg, SpO2, EtCO2), and pulmonary function testing (especially negative inspiratory force) aid in identifying subtle deterioration that may herald impending respiratory failure. (See "Overview of pulmonary function testing in children" and "Simple and mixed acid-base disorders", section on 'Response to respiratory acidosis'.)

Electrolyte abnormalities – Electrolyte measurements may identify an electrolyte disturbance that is the primary cause of weakness or show abnormalities in potassium associated with rhabdomyolysis (hyperkalemia) or periodic paralysis (hypokalemia or hyperkalemia). An elevated creatine kinase is seen in patients with myositis, rhabdomyolysis, dermatomyositis, and other myopathies.

Urinalysis – Urinalysis may show reddish brown pigment in patients with rhabdomyolysis and will have measurable myoglobin.

Neuroimaging – Patients with focal muscle weakness suggestive of central or spinal cord lesions warrant appropriate neuroimaging. Emergent computed tomography of the brain should be performed in patients with suspected brain tumor, stroke, or intracranial hemorrhage. Emergent magnetic resonance imaging (MRI) of the spine should be obtained in children with evidence of a spinal cord tumor, hematoma, or abscess. Standard imaging for patients with suspected acute flaccid myelitis includes MRI of the cervical and thoracic spine with and without contrast and MRI of the brain with and without contrast.

Edrophonium or ice pack testing – After consultation with a pediatric neurologist, ice pack testing may be helpful in the diagnosis of pediatric patients with findings suggestive of myasthenia gravis. Edrophonium has fallen out of use due to poor test characteristics and adverse events. The medication is no longer available in many countries. (See "Diagnosis of myasthenia gravis", section on 'Clinical testing'.)

Specialized electrophysiologic testing of muscle and nerve function for diagnostic purposes should be obtained in association with pediatric neurological consultation. (See "Overview of electromyography" and "Overview of nerve conduction studies".)

DIAGNOSTIC APPROACH — The approach to a child with weakness depends on the acuity of the presentation.

Sudden onset, severe weakness — Patients with a history of trauma followed by immediate weakness require prompt neuroimaging and consultation with a neurosurgeon in anticipation of an intracranial hemorrhage or spinal cord injury (algorithm 1).

Immediate onset weakness after a seizure requires close assessment for rapid improvement typically seen in patients with Todd paralysis. If weakness persists, then the possibility of a seizure in association with a stroke, subarachnoid hemorrhage, or brain tumor should be pursued.

Rapid onset weakness in association with headache or other signs of increased intracranial pressure in the absence of trauma or seizure suggests the presence of stroke, subarachnoid hemorrhage, or brain tumor with hemorrhage.

Acute-onset weakness — The following considerations assist in identifying the cause of acute onset of weakness (within hours to days) (algorithm 2):

Recent seizure in a patient with proximal muscle weakness and tenderness of large muscle groups (rhabdomyolysis)

Constipation, weak suck, and progressive weakness in an infant (infant botulism)

Recent ingestion of barrier reef fish (eg, mahi-mahi), shellfish, undercooked pork, or home canned food (ciguatera poisoning, paralytic shellfish poisoning, trichinellosis, or botulism), or neurotoxic envenomation

Exposure to medications (table 5) known to cause weakness or to precipitate acute intermittent porphyria (table 3) or toxin exposure (eg, organophosphates, carbamates, heavy metals)

Presence of fever (viral myositis, pyomyositis, trichinellosis) or antecedent upper respiratory infection (acute flaccid myelitis [AFM])

Headache (acute hemisyndrome migraine, brain tumor, stroke, subarachnoid hemorrhage)

Neck or back pain (Guillain-Barré, poliomyelitis, transverse myelitis, epidural hematoma or abscess)

Attached engorged tick (tick paralysis) or infected wound (wound botulism)

Presence of an inciting event or psychologic stress in concert with physical examination features suggestive of conversion disorder

Subacute or chronic weakness — The clinician should assess children with subacute or chronic weakness for signs of increased intracranial pressure (headache, morning vomiting, focal neurologic signs) that would indicate a brain tumor (algorithm 3).

Patients whose weakness is exacerbated by exercise should undergo additional evaluation for myasthenia gravis, periodic paralysis, myotonic dystrophy, and/or rhabdomyolysis depending upon family history, physical findings, and laboratory studies.

Gottron papules on the hands, facial heliotrope rash (picture 1), periungual capillary changes, and dystrophic calcification (picture 2) are findings of dermatomyositis in children.

Weakness that is greater in the proximal muscle groups is typical for muscle disorders such as spinal muscular atrophy, muscular dystrophy, congenital myopathies, congenital hypothyroidism, or Cushing's syndrome. Of note, patients with spinal muscular atrophy have cranial nerve involvement with difficulty swallowing.

Distal muscle weakness is more suggestive of a neurodegenerative process (eg, juvenile amyotrophic lateral sclerosis) or a chronic neuropathy. (See "Overview of acquired peripheral neuropathies in children".)

SUMMARY AND RECOMMENDATIONS

Definition – Weakness is a decreased ability to voluntarily and actively move muscles against resistance. Weakness may arise from any portion of the motor unit and is typically divided into upper motor neuron and lower motor neuron weakness. (See 'Definitions' above.)

Acute weakness – The causes of acute weakness are provided in the table (table 1). Many of the conditions that cause acute muscle weakness are potentially life-threatening. Mortality due to acute muscle weakness is typically caused by respiratory failure or by lesions in the brain that cause both weakness and increased intracranial pressure (see 'Causes of acute weakness' above):

Upper motor neuron lesion – Patients with acute upper motor neuron lesions may initially present with altered mental status and focal neurologic findings such as unequal pupils, visual field defects, cranial nerve palsies, and/or paralysis on the opposite side of the central nervous system lesion. During the acute phase, upper motor neuron lesions are associated with decreased spinal cord reflexes and hypotonia. Over the period of several weeks, spasticity, hyperreflexia, and “upper motor neuron” signs (eg, positive Babinski sign) develop. (See 'Upper motor neuron lesion' above.)

Lower motor neuron lesion – Patients with lower motor neuron weakness typically display muscle weakness, hypotonia, fasciculations, and decreased spinal cord reflexes. Mental status is typically, but not always preserved depending upon the cause and whether respiratory failure has occurred. (See 'Lower motor neuron lesion' above.)

Chronic weakness – Important causes of chronic weakness in children are shown in the table (table 6). Of these, congenital hypothyroidism and Cushing's syndrome are important conditions to recognize because they are reversible with prompt treatment. (See 'Causes of chronic weakness' above.)

Stabilization – Initial evaluation of a child with weakness should focus on the child's airway, breathing, and circulation with careful assessment of respiratory effort, air movement, and pulse oximetry. The presence of Cushing's triad (bradycardia, hypertension, and irregular respirations) or altered mental status should prompt emergency evaluation for and treatment of increased intracranial pressure. (See 'Initial stabilization' above.)

Diagnostic approach – The diagnostic approach to the child with muscle weakness is summarized in the algorithms (algorithm 1 and algorithm 2 and algorithm 3). Assessment should focus on key historical and physical examination findings that help narrow the extensive differential diagnosis (table 1). (See 'Evaluation' above.)

Topic 6442 Version 22.0

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