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Evaluation of weight loss in infants six months of age and younger

Evaluation of weight loss in infants six months of age and younger
Literature review current through: Jan 2024.
This topic last updated: Oct 04, 2022.

INTRODUCTION — This topic will discuss the approach to weight loss in the infant who is six months of age and younger. The evaluation of weight loss in older infants, children, adolescents, and adults is discussed separately. (See "Evaluation of weight loss in infants over six months of age, children, and adolescents" and "Approach to the patient with unintentional weight loss".)

BACKGROUND — Weight loss is often seen in the first week of life, with healthy newborns losing 7 to 10 percent of their birth weight as milk production is established in the first 72 hours postpartum. Neonates typically regain that weight by two weeks of life, with most gaining approximately 1 ounce (30 grams) per day. (See "Normal growth patterns in infants and prepubertal children", section on 'Typical milestones'.)

Ongoing weight loss in young infants is commonly caused by acute infection, problems with feeding, milk protein allergy, malnutrition, or failure to thrive. Gastroesophageal reflux disease, pyloric stenosis, and child neglect are other frequent etiologies. Dehydration associated with any etiology can be severe.

Although less common, other life-threatening conditions include intestinal malrotation with volvulus, congenital heart disease, congenital adrenal hyperplasia, and inborn errors of metabolism. A careful, thorough history and physical examination, in conjunction with the judicious use of laboratory tests, will often reveal the cause.

PATHOPHYSIOLOGY — The major components of weight include water, protein, carbohydrates, and fats. Weight loss occurs when the daily balance of one or several of these components becomes negative. During infancy and early childhood, major causes of weight loss include inadequate calorie intake to meets the energy demands of the child's metabolism for daily activity and growth, or negative fluid balance. Specific etiologies include (see "Poor weight gain in children younger than two years in resource-abundant settings: Etiology and evaluation", section on 'Causes'):

Decreased calorie intake

Normal calorie intake with an increased metabolic need

Normal calorie intake in the setting of malabsorption or excessive loss.

During acute illnesses, such as gastroenteritis, fluid losses that exceed intake can lead to significant weight loss. (See "Clinical assessment of hypovolemia (dehydration) in children".)

DIFFERENTIAL DIAGNOSIS — The differential diagnosis for weight loss in the young infant is wide and may require an extensive work-up (table 1). In many patients, a diagnosis is not established during an initial visit, but the evaluation may begin and specialist referrals made as needed.

Life-threatening conditions

Dehydration — Severe dehydration from acute gastroenteritis can lead to significant weight loss from fluid losses. Dehydration from gastroenteritis is one of the leading causes of death among infants in developing nations. Infants with acute gastroenteritis typically present with acute onset of diarrhea, vomiting, fever, and decreased feeding. Blood or mucous in the stool or rice water stool suggest bacterial enteritis or cholera, respectively. Dehydration may also occur due to other acute infections (eg, pneumonia, sepsis, urinary tract infection), conditions causing decreased intake (eg, feeding disorders, congenital heart disease, child neglect, malnutrition) or conditions associated with increased loses (eg, gastroesophageal reflux disease, pyloric stenosis, milk protein allergy with diarrhea, or intestinal malabsorption). Findings of significant dehydration (eg, prolonged capillary refill, dry mucous membranes, sunken eyes or fontanelle, or lethargy) are commonly found on physical examination. (See "Clinical assessment of hypovolemia (dehydration) in children", section on 'Clinical assessment'.)

Repletion of fluid losses and management of gastroenteritis are discussed in more detail separately. (See "Treatment of hypovolemia (dehydration) in children in resource-abundant settings" and "Diagnostic approach to diarrhea in children in resource-abundant settings", section on 'Algorithmic approach to the patient'.)

Intermittent intestinal malrotation — Rotational anomalies occur as a result of an arrest of normal rotation of the embryonic gut. Volvulus occurs when small bowel twists around the superior mesenteric artery resulting in vascular compromise to large portions of the midgut (figure 1). Most children with intestinal malrotation develop signs of acute small bowel obstruction in early infancy. Intestinal malrotation should be suspected in any infant with bilious vomiting. Physical examination may reveal mild distension of the abdomen, diffuse tenderness with or without signs of peritonitis, and bloody stool on rectal examination. Blood in the stool is a worrisome sign, since it suggests bowel ischemia and possible necrosis from volvulus. Third space fluid losses and sepsis, caused by necrotic bowel, can cause rapidly progressive cardiovascular compromise. Prompt fluid resuscitation and surgical intervention are essential. (See "Intestinal malrotation in children", section on 'Embryology and pathogenesis' and "Intestinal malrotation in children", section on 'Clinical presentation'.)

If the child is hemodynamically stable, the diagnosis should be confirmed by radiologic evaluation. This evaluation typically begins with plain radiographs, which are rarely diagnostic, but are important to exclude obvious perforation indicated by pneumoperitoneum. Plain radiographs are followed by an upper gastrointestinal contrast series, which is the best examination to visualize the duodenum in infants and children. It should be performed, whenever possible, under fluoroscopy by an experienced pediatric radiologist. (See "Intestinal malrotation in children", section on 'Diagnosis'.)

Congenital heart disease — Congenital heart disease (CHD) is the most common congenital disorder in newborns; ventricular septal defects account for approximately half of malformations. Infants with congenital heart disease frequently have difficulty feeding with resulting weight loss from dehydration or protein-calorie malnutrition. Though cyanotic and ductal dependent heart lesions are typically diagnosed perinatally and up to two weeks of age, many cardiac lesions (eg, structural lesions, cardiomyopathies, and cardiac tumors) may present later in infancy with weight loss or poor weight gain. (See "Identifying newborns with critical congenital heart disease", section on 'Postnatal diagnosis'.)

In affected infants, parents/caregivers most commonly notice difficulty with feeding. This may be manifested by intake of a limited volume of milk. Feedings may also take too long due to frequent interruption by sleeping or resting, choking, gagging, and/or vomiting. Infants may have respiratory distress that is reported by caregivers as fast or hard breathing, worse with feedings, or a persistent cough or wheeze. Other manifestations include color changes, such as central cyanosis or persistent pallor; excessive sweating that is increased with feeding and occurs during sleep, decreased activity, or excessive sleeping. Physical examination may demonstrate a cardiac murmur, gallop, or decreased pulses in the lower extremities. Electrocardiogram, chest radiograph, echocardiogram and consultation with a pediatric cardiologist should be performed for any infant in whom congenital heart disease is suspected. (See "Identifying newborns with critical congenital heart disease", section on 'Signs and symptoms'.)

Congenital adrenal hyperplasia — Inherited defects in the enzymatic steps of cortisol biosynthesis (steroidogenesis) result in disease states termed congenital adrenal hyperplasia (CAH) (figure 2). These disorders cause primary adrenal insufficiency because they impair cortisol synthesis (table 2).

CYP21A2 (21-hydroxylase) deficiency is the most common form of CAH (figure 2). It accounts for more than 95 percent of cases of adrenal steroidogenic defects, and is estimated to occur in one in 14,200 live births. CYP21A2 deficiency usually presents as one of two clinical syndromes in neonates or very young infants, both of which are associated with glucocorticoid deficiency: a salt-wasting form (hyponatremia, hyperkalemia, and hypotension on account of mineralocorticoid deficiency) with ambiguous genitalia in affected females (because of adrenal androgen excess), and a simple virilizing form in affected males and females without salt wasting. In some infants, the distinction between the two forms is not clear. Adrenal crisis with circulatory collapse may occur within the first few days to weeks of life. In the United States, 21-hydroxylase deficiency is part of the newborn screen in all states, so most affected infants are diagnosed prior to developing adrenal crisis. (See "Genetics and clinical manifestations of classic congenital adrenal hyperplasia due to 21-hydroxylase deficiency".)

The treatment of adrenal insufficiency and adrenal crisis in patients with primary adrenal insufficiency is discussed separately (table 3). (See "Treatment of adrenal insufficiency in children".)

Inborn error of metabolism — Metabolic disorders result from the absence or abnormality of an enzyme or its cofactor, leading to either accumulation or deficiency of a specific metabolite [1]. Patients often present during the neonatal period in acute metabolic decompensation from vomiting and significant dehydration. This weight loss is associated with laboratory abnormalities (eg, hypoglycemia, lactic acidosis, or hyperammonemia). Additional findings may include lethargy, coma, seizures, and abnormal odors. Partial or mild defects may present with a milder course and in later childhood. (See "Metabolic emergencies in suspected inborn errors of metabolism: Presentation, evaluation, and management", section on 'Laboratory findings'.)

Most episodes of metabolic decompensation due to IEM are associated with one or more of the following metabolic derangements that are typically part of the routine assessment of a patient with one of the clinical presentations mentioned above (table 4 and table 5) (see "Metabolic emergencies in suspected inborn errors of metabolism: Presentation, evaluation, and management", section on 'Laboratory findings'):

Acid-base disorder (including lactic acidosis)

Hyperammonemia

Hypoglycemia

Sepsis-like features secondary to bone marrow suppression (eg, galactosemia)

An abnormal laboratory value may be the first finding noted that suggests an IEM. In some disorders, these laboratory abnormalities are only present during the episode of metabolic decompensation. (See "Metabolic emergencies in suspected inborn errors of metabolism: Presentation, evaluation, and management", section on 'Evaluation of specific critical presentations'.)

The initial evaluation and management of an infant with a suspected inborn error of metabolism is discussed in detail separately. (See "Metabolic emergencies in suspected inborn errors of metabolism: Presentation, evaluation, and management", section on 'Initial evaluation' and "Metabolic emergencies in suspected inborn errors of metabolism: Presentation, evaluation, and management", section on 'Evaluation of specific critical presentations' and "Metabolic emergencies in suspected inborn errors of metabolism: Presentation, evaluation, and management", section on 'Immediate management'.)

Common conditions

Acute infection — Patients with underlying acute infections can present with weight loss due to decreased ability to feed in conjunction with increased metabolic needs. Young infants often present with lethargy or decreased activity, fever, hypothermia, or respiratory distress due to a variety of illnesses including sepsis, bronchiolitis or other viral infections, urinary tract infection, or pneumonia. (See "The febrile infant (29 to 90 days of age): Outpatient evaluation".)

Feeding disorder — Feeding disorders can include anatomic, medical, or behavior problems, or result from developmental immaturity [2]. These problems often interfere with the coordination of sucking, swallowing, and breathing and may lead to weight loss or poor weight gain in the young infant. Premature infants, children with anatomic malformations of the oropharynx or esophagus (eg, cleft lip and palate or tracheo-esophageal fistula), neuromuscular weakness including infant botulism, or chronic neurologic disorders (eg, cerebral palsy or neuromuscular weakness) are at highest risk. (See "Neonatal oral feeding difficulties due to sucking and swallowing disorders", section on 'Etiology'.)

Prematurely born infants and those requiring prolonged endotracheal intubation early in life may be at increased risk of having oral aversion. Some infants become extremely sensitive to certain textures and may refuse food intake. This aversion can range from a mild intolerance to textured foods to a complete refusal to take anything by mouth. A psychologist, speech therapist, or occupational therapist experienced in working with feeding disorders should be consulted as soon as a problem when oral aversion is suspected. A thorough evaluation will be needed to establish the range of factors involved and to rule out unidentified physiological problems. (See "Neonatal oral feeding difficulties due to sucking and swallowing disorders", section on 'Management approach'.)

Patients with neuromuscular disease may present with poor weight gain or weight loss in association with generalized weakness, hypotonia, and feeding difficulty. Problems with sucking and swallowing are common in infants with central nervous system or neuromuscular disorders. In addition, difficulty maintaining airway patency and clearing secretions can predispose these patients to recurrent respiratory infections, which increases metabolic demand. Patients with significant disease must often maintain long term daily nutritional requirements through feeding tubes or parenteral supplementation. (See "Neonatal oral feeding difficulties due to sucking and swallowing disorders", section on 'Management approach'.)

Infant botulism is a rare but life-threatening illness resulting from intestinal colonization by Clostridium botulinum. In addition to decreased feeding, affected infants have progressive weakness (descending global hypotonia), weak cry, and constipation. (See "Neuromuscular junction disorders in newborns and infants", section on 'Infant botulism'.)

Gastroesophageal reflux disease — Gastroesophageal reflux is common in infants and is usually not pathological. Regurgitation is present in 50 to 70 percent of all infants, peaks at age four months, and typically resolves by one year. In contrast, gastroesophageal reflux disease (GERD) occurs when the reflux episodes are associated with symptoms or complications. A small minority of infants with GERD develop other symptoms, including feeding refusal, irritability possibly secondary to pain during eating, hematemesis, anemia, respiratory symptoms, and failure to thrive. Decreased food intake without any other complaints may be a symptom of esophagitis in infants, which can cause weight loss. In some infants, the pain of esophagitis causes arching of the back, extension of the neck, and turning of the head to the side in associated with regurgitation or choking (Sandifer syndrome). Color change (pallor or cyanosis) may also occur. These episodes may be mistaken for seizures, apnea, or dystonia. GERD is a clinical diagnosis. In patients who do not respond to treatment, upper endoscopy with biopsy of the esophagus, stomach, or duodenum may be indicated. (See "Gastroesophageal reflux in infants", section on 'Clinical approach' and "Gastroesophageal reflux in infants", section on 'Diagnostic tests'.)

Pyloric stenosis — Patients with pyloric stenosis may present to the ED with dehydration and acute weight loss due to persistent vomiting. The classic presentation is a three to six-week-old first-born male infant who develops immediate postprandial, non-bilious, often projectile vomiting and demands to be re-fed soon afterwards (a "hungry vomiter"). Vomiting may be less forceful in premature infants and those with central nervous system anomalies or cleft lip and palate. Significant dehydration with hemodynamic instability can occur. Laboratory evaluation classically shows a hypochloremic, metabolic alkalosis resulting from the loss of large amounts of gastric hydrochloric acid. The severity of these laboratory abnormalities depends upon the duration of symptoms prior to initial evaluation. Diagnosis is made by palpation of the hypertrophic pylorus or by demonstration of characteristic findings on ultrasound or an upper gastrointestinal study with contrast swallow. (See "Infantile hypertrophic pyloric stenosis", section on 'Clinical manifestations' and "Infantile hypertrophic pyloric stenosis", section on 'Diagnosis'.)

Child abuse and neglect — Child neglect is the most prevalent form of child abuse, accounting for more than one-half of cases reported to child protection services. It is defined by the National Center of Child Abuse and Neglect as failure to provide for a child's basic physical, emotional, educational, or medical needs. The manifestations of infant neglect leading to weight loss may include starvation or dehydration due to inadequate provision of food and water, poor hygiene of an infant's body, failure to provide for the infant's medical needs, and physical abuse. Many, but not all neglected infants will also have physical signs of abuse including fractures and bruises. (See "Child neglect: Evaluation and management".)

Milk protein allergy — Cow's milk protein allergy (CMA) is the most common food allergy in young infants and children, affecting about two percent of all children under four years of age. Clinical symptoms of cow's milk protein allergy frequently appear during the first few months of life, often within days or weeks after the introduction of a cow's milk-based formula into the diet, although symptoms may also occur with exclusive breastfeeding if the mother ingests cow's milk. Patients typically present with weight loss in association with vomiting, diarrhea, abdominal distension, and/or bloody stools though patients can also present with atopy, anaphylaxis, or more severe gastrointestinal disease (table 6). (See "Milk allergy: Clinical features and diagnosis", section on 'Clinical features'.)

The diagnosis of CMA is based upon the history and laboratory testing, when available (diagnostic tests for non-IgE-mediated manifestations of CMA are limited). The gold-standard for diagnosis is a clinician-supervised double-blind, placebo controlled oral food challenge, although an open challenge will often suffice. Measurement of cow's milk-specific IgE can aid in the diagnosis of IgE-mediated CMA and may eliminate the need for oral food challenges. (See "Oral food challenges for diagnosis and management of food allergies".)

Malnutrition and failure to thrive — A detailed social history can often reveal poverty and economic stressors as potential contributors to weight loss from lack of resources. Infants may present with weight loss or poor weight gain because of decreased intake due to the inability to acquire adequate amounts of nutrition and chronic conditions that are due to poor food availability [3]. Often, patients have no reliable housing and other social stressors that need attention.

Malnutrition may also occur inadvertently when inexperienced parents/caregivers add too much water to powdered or concentrated formula [4]. Likewise, parents/caregivers may choose a specific diet (vegetarian, vegan, etc) to fit their family goals. While a completely plant-based diet is potentially suitable during all stages of life, it must be well-planned to avoid malnutrition and deficiencies in a growing infant. (See "Vegetarian diets for children".)

Failure to thrive (FTT) is a term that describes a particular problem, rather than a diagnosis. FTT is used to describe instances of growth failure or, more specifically, failure to gain weight appropriately [5]. In more severe cases, linear growth and head circumference also may be affected. A wide variety of medical problems and psychosocial stressors can contribute to FTT (table 7); however, the underlying cause is always "insufficient usable nutrition". Several definitions of failure to thrive exist. All definitions identify infants with failure to thrive as having low weight in relation to age or length or insufficient weight gain over time. (See "Poor weight gain in children younger than two years in resource-abundant settings: Etiology and evaluation" and "Poor weight gain in children younger than two years in resource-abundant settings: Management".)

Because of increased caloric and nutritional needs, former premature infants are at risk for inadequate growth and require close monitoring and specific nutritional interventions, as discussed separately. (See "Growth management in preterm infants".)

Other conditions — A variety of less common but important conditions may present with weight loss as follows:

Human immunodeficiency virus – Clinical manifestations of human immunodeficiency virus (HIV) infection in infants and children are varied and often nonspecific. During the first year of life, lymphadenopathy, oral candidiasis, failure to thrive, and developmental delay are common presenting features of HIV infection. Infants may present with recurrent unexplained infections leading to gradual weight loss and failure to thrive. The approach to diagnostic testing for HIV in infants is discussed in detail separately. (See "Epidemiology of pediatric HIV infection" and "Pediatric HIV infection: Classification, clinical manifestations, and outcome" and "Diagnostic testing for HIV infection in infants and children younger than 18 months", section on 'Diagnostic strategies'.)

Primary immunodeficiency – Infants with primary immunodeficiency often have poor weight gain or weight loss. This is particularly true in the presence of oral ulcers, candidiasis, or chronic diarrhea. Almost three-fourths of the primary immunodeficiencies are caused by an antibody (B cell) deficiency or a combined antibody plus cellular (T cell) abnormality (figure 3). Isolated T cell defects, as well as phagocytic cell, complement, and other innate immune defects, are much less common. Thus, B cell (antibody) or combined B and T cell diseases should be considered initially, unless clinical features suggest otherwise. Recurrent infections comprise the most common clinical findings. The type and pattern of recurring infections depend upon which components of the immune system are affected (table 8). Infection severity also varies, ranging from mild respiratory infections to overwhelming systemic infections. (See "Approach to the child with recurrent infections", section on 'Clinical features suggestive of a primary immunodeficiency'.)

Intestinal malabsorption – Weight loss in association with congenital chronic diarrhea can be caused by a variety of inherited disorders that disrupt nutrient digestion, absorption or transport, enterocyte development and function, or enteroendocrine function. Specific genes have been identified for some of these disorders (table 9). If a congenital diarrhea is suspected, stool electrolytes, pH, fat, and reducing substances should be measured. A trial of fasting should be performed to determine if the diarrhea is secretory or osmotic. Further evaluation of congenital secretory and osmotic diarrhea is discussed separately. (See "Approach to chronic diarrhea in neonates and young infants (<6 months)".)

Kidney disease – Renal tubular acidosis (RTA) may present as poor growth in infancy. The most common form is isolated proximal RTA (sporadic or transient infantile RTA). Diagnosis is based upon the results of blood and urine studies (table 10) as described in detail separately. (See "Etiology and diagnosis of distal (type 1) and proximal (type 2) renal tubular acidosis" and "Etiology and clinical manifestations of renal tubular acidosis in infants and children".)

Acute kidney injury (AKI) is a rare cause of weight loss in newborns and young infants. It should be suspected in patients who have an elevated or rising serum creatinine, anuria, or oliguria. Oligoanuria is defined as no urine output noted by 48 hours of age or a diminished urine output (urine volume less than 1.0 mL/kg per hour). Although the time of the first void is variable, at least 50 percent of newborns void by eight hours of age and nearly all before 24 hours. However, the presence of urine does not rule out AKI since some infants are nonoliguric. The diagnosis of neonatal AKI is confirmed by either a serum creatinine level >1.5 mg/dL (133 micromol/L) or increases by at least 0.2 to 0.3 mg/dL (17 to 27 micromol/L) per day. The evaluation and causes of neonatal AKI discussed in detail separately. (See "Neonatal acute kidney injury: Evaluation, management, and prognosis", section on 'Identifying the underlying cause'.)

Liver disease – Chronic liver disease may be associated with weight loss in young infants and is associated with jaundice due to direct hyperbilirubinemia. Causes include biliary atresia, metabolic disorders (eg, galactosemia), infectious hepatitis (eg, infection with toxoplasmosis, rubella, cytomegalovirus, herpes and syphilis [TORCH infections]), and idiopathic neonatal hepatitis. (See "Causes of cholestasis in neonates and young infants".)

Chronic lung disease – Infants with chronic lung disease (eg, bronchopulmonary dysplasia) may have increased energy expenditure because of increased work of breathing and recurrent respiratory illnesses. Many patients will have recurrent or persistent wheezing, increased respiratory rate and effort, feeding difficulties, and weight loss. (See "Bronchopulmonary dysplasia (BPD): Clinical features and diagnosis", section on 'Clinical features'.)

Cystic fibrosis (CF) is the most common fatal autosomal recessive disease among White populations, with a frequency of 1 in 2000 to 3000 live births. Presentations in young infants include meconium ileus at birth, wheezing, coughing, recurring respiratory infections and pneumonia and/or gastrointestinal malabsorption with steatorrhea and failure to thrive. Screening for CF is performed at birth in most resource-rich countries. Diagnosis is confirmed with the presence of an elevated sweat chloride test. For optimal accuracy, sweat testing should be performed when the infant is at least two weeks of age and weighs >2 kg. (See "Cystic fibrosis: Clinical manifestations and diagnosis", section on 'Overview of clinical features' and "Cystic fibrosis: Clinical manifestations and diagnosis", section on 'Newborn screening'.)

Malignancy – Cancer is rare in infants ≤6 months but may present with fever, abdominal mass (eg, stage 4S neuroblastoma or Wilms tumor), or pallor and easy bruising or bleeding (eg, acute leukemias). (See "Overview of common presenting signs and symptoms of childhood cancer".)

APPROACH — The diagnostic approach to the cause of weight loss in infants six months of age and younger and a list of etiologies are summarized in the algorithm and table, respectively (algorithm 1 and table 1).

Infants with ill appearance require timely resuscitation and treatment of dehydration and shock as needed. In addition to acute infection, these patients should be carefully assessed for findings of congenital heart disease, intestinal malrotation with volvulus, congenital adrenal hyperplasia, inborn error of metabolism, and malignancy. In patients with early presentations of some diseases that usually cause significant illness, such as malrotation or congenital adrenal hyperplasia, appearance may be normal.

Poor feeding, child abuse and neglect, pyloric stenosis and gastroenteritis are common conditions causing dehydration. In patients with these conditions, dehydration may be severe and cause ill appearance.

Among infants who are hemodynamically stable, the etiology of weight loss may be identified by the presence of the following findings (see 'Differential diagnosis' above):

Vomiting – Nonbilious vomiting is associated with pyloric stenosis or gastroesophageal reflux disease.

Fever – Fever commonly indicates an acute infection (eg, urinary tract infection, gastroenteritis, or pneumonia) or rarely, malignancy.

Abnormal stools – Malodorous or frequent loose stools may occur with intestinal malabsorption from malnutrition, cystic fibrosis or, rarely, congenital malabsorption syndromes. Bloody stools suggest milk protein allergy or bacterial enteritis. Diarrhea with or without vomiting is frequently caused by viral or bacterial gastroenteritis.

Recurrent infections – Recurrent infections are concerning for human immunodeficiency virus infection or primary immunodeficiency.

Jaundice – Jaundice, especially caused by direct hyperbilirubinemia and associated with elevated liver enzymes, indicates liver disease.

Urinary abnormalities – Oliguria or anuria is associated with elevated serum creatinine, and blood urea nitrogen suggests kidney disease.

Failure to thrive and malnutrition – Improper mixing of formula, intentional diluting of formula due to poverty, or child neglect all cause malnutrition with failure to thrive. Poor hygiene, lack of proper medical care, or suspicious bruises or fractures suggest child abuse and neglect.

Feeding disorder – Poor feeding may be caused by an anatomic defect (eg, cleft lip and palate or tracheo-esophageal fistula) or poor suck due to oral aversion or neuromuscular weakness.

EVALUATION — The goal of the evaluation of a young infant with weight loss is to identify any signs and symptoms of underlying disease, especially congenital disease, or potential psychosocial factors, primarily child neglect, that may be involved. In the stable, relatively well-appearing patient, a careful, thorough history and physical examination, in conjunction with the judicious use of laboratory tests will often reveal the cause. Laboratory investigation is unlikely to reveal an organic cause in the absence of suggestive evidence from the initial history or physical examination.

History — The clinician should begin by determining the severity and timing of weight loss:

Severe, rapid weight loss – Rapid weight loss over a few days in a young infant is more indicative of a life-threatening process and needs prompt evaluation and treatment. Acute weight loss is often caused by inadequate fluid and caloric intake, increased losses fluid, or increased metabolic needs associated with an intercurrent illness.

Important historical features that suggest specific etiologies include (see 'Life-threatening conditions' above):

Bilious vomiting (see 'Intermittent intestinal malrotation' above)

Tachypnea, diaphoresis, or cyanosis with feeding (see 'Congenital heart disease' above)

History of ambiguous genitalia in a female infant or a positive screen for congenital adrenal hyperplasia (see 'Congenital adrenal hyperplasia' above)

Acute decompensation in the neonatal period with lethargy, vomiting, seizures, and/or abnormal odors (see 'Inborn error of metabolism' above)

History of fever, feeding difficulty, vomiting, and/or diarrhea with decreased urine output suggesting dehydration. Of note, severe symptoms from common conditions, such as acute infection (eg, gastroenteritis, urinary tract infection, pneumonia), pyloric stenosis, or feeding disorder may cause significant dehydration (see 'Common conditions' above)

Persistent, moderate weight loss – Young infants with weight loss persisting over one to two weeks without severe decompensation warrant a careful feeding history as well as questioning about regurgitation, vomiting, diarrhea, hematochezia, steatorrhea, and acholic stools. The clinician should also review the perinatal history with a focus on gestational age at birth, exposure to TORCH infections (eg, toxoplasmosis, syphilis, rubella, cytomegalovirus, or herpes simplex virus infection), and any concern for congenital malformations at birth or by prenatal ultrasound screening. If the patient is fed using powdered formula or other preparations that are not "ready-to-feed," the clinician should assess whether the caregiver is properly mixing the formula.

Specific etiologies are suggested by the following historical findings:

Prematurity, bronchopulmonary dysplasia, neuromuscular disease (eg, cerebral palsy or weakness), or anatomic malformations (eg, cleft lip and palate) causing difficulty with feeding (see 'Feeding disorder' above and 'Other conditions' above)

Symptoms of gastroesophageal reflux disease including feeding refusal, irritability with feedings, hematemesis, or arching and turning of the head (Sandifer syndrome) in association with frequent regurgitation while eating (see 'Gastroesophageal reflux disease' above)

Postprandial, nonbilious, often forceful vomiting occurring around four weeks of age and associated with demands for re-feeding soon after emesis ("hungry vomiter") in infants with pyloric stenosis (see 'Pyloric stenosis' above)

Poverty associated with inadequate breastfeeding or supply of formula (see 'Malnutrition and failure to thrive' above)

Drug use in one or both caregivers, prior placement of siblings into foster care, and poor compliance with recommended medical care suggesting child abuse and neglect

Vomiting, diarrhea, abdominal distension, and/or blood stools starting within days or weeks after the introduction of a cow's milk-based formula or in breastfeeding infants in whom the mother ingests cow's milk (see 'Milk protein allergy' above)

Oliguria or anuria in a newborn infant indicates acute kidney injury

Frequent, recurrent infections suggesting primary immunodeficiency or human immunodeficiency virus (HIV) infection (see 'Other conditions' above)

Chronic diarrhea since birth consistent with congenital chronic diarrhea (see 'Other conditions' above)

A complete dietary history should be investigated, including type of intake (breast milk, milk protein-based or soy-based formula, etc), quantity, and frequency. (See "Dietary history and recommended dietary intake in children", section on 'Dietary history in infants'.)

Physical examination — Patients with signs of shock warrant prompt interventions for the treatment of physiological derangements, including support of airway and breathing, rapid vascular access, and rapid administration of isotonic intravenous fluids (algorithm 2) followed by a comprehensive examination. (See "Shock in children in resource-abundant settings: Initial management".)

The weight should be obtained and compared with prior measurements along with length and head circumference. These measurements should be plotted on the appropriate growth chart and compared with any previously available measurements to assess for rate of loss and changes in weight percentile (see "Normal growth patterns in infants and prepubertal children", section on 'Growth charts'). Failure of adequate growth in head circumference in association with weight loss is of particular concern in young infants. (See "Poor weight gain in children younger than two years in resource-abundant settings: Etiology and evaluation".)

Term neonates may normally lose up to 10 percent of their birth weight in the first few days of life but should regain their birth weight by 14 days of age. Infants typically double their birth weight by four months of age. (See "Normal growth patterns in infants and prepubertal children", section on 'Weight gain in children <2 years'.)

Direct observation of the infant feeding frequently provides important information regarding the cause of weight loss. Any accompanying respiratory distress, sweating, or choking with feeds should be noted as they may be associated with an underlying cause of poor weight gain. Additionally, any difficulty with breastfeeding, infant latch, painful nipples, or mastitis should be noted.

Physical findings that suggest potential etiologies include:

General appearance – Increased fussiness is associated with gastroesophageal reflux disease, milk protein allergy, and congenital heart disease. Fussiness and arching during observed feeding can be a sign of gastroesophageal reflux disease with esophagitis (Sandifer syndrome). Poor hygiene and suspicious bruising suggests child abuse and neglect.

Abnormal odor of the patient's breath, urine (table 11), perspiration, saliva, or cerumen should prompt consideration of organic acidemias, amino acid disorders, urea cycle defects, and fatty acid oxidation disorders. However, the majority of patients who have an unusual odor do not have an IEM or other underlying medical cause for the odor. (See "Inborn errors of metabolism: Epidemiology, pathogenesis, and clinical features", section on 'Abnormal odors'.)

Fever – Fever may be present in infants with acute infection or, rarely, malignancy.

Compensated shock or hypotension – Tachycardia with prolonged capillary refill time or hypotension may occur in infants with congenital adrenal hyperplasia, dehydration, decompensated congenital heart disease, intestinal malrotation with volvulus, inborn errors of metabolism, or serious acute infections.

Cardiopulmonary abnormalities – Tachypnea at rest may suggest chronic lung disease or congenital heart disease. Congenital heart disease is also suggested by diaphoresis, cardiac murmur or gallop, rales, or femoral pulses that are weaker than upper extremity pulses.

Oral findings – Cleft lip and palate are usually obvious on direct observation but occasionally are subtle in extent. During feeding, oral aversion or a weak suck may be evident.

Additionally, ankyloglossia or "tongue-tie" can lead to weight loss in breastfed infants. If unable to move the nipple into correct position, the infant might chew instead of suck on the nipple, causing significant discomfort and interfering in breastmilk delivery. Ultimately, poor breastfeeding can lead to inadequate nutrition and failure to thrive and is an indication for surgical management if conservative measures fail. (See "Ankyloglossia (tongue-tie) in infants and children", section on 'Surgical procedures'.)

Abdominal distension or mass – Several causes of weight loss may present with abdominal findings:

Abdominal distension with tenderness may occur in infants with intestinal malrotation and volvulus.

Pyloric stenosis may present with an olive-sized mass in the right upper quadrant and projectile vomiting after feeding.

A palpable bladder in a male infant shortly after voiding may indicate posterior urethral valves with associated acute kidney injury.

Flank masses may arise from a neuroblastoma or Wilms tumor.

Jaundice – Jaundice from direct hyperbilirubinemia has a greenish hue relative to physiologic jaundice and is associated with sepsis, liver disease, metabolic disease (eg, galactosemia), and perinatal infections (eg, infection with toxoplasmosis, rubella, cytomegalovirus, herpes, and syphilis [TORCH infections]).

Genitourinary findings – Ambiguous genitalia in females is associated with congenital adrenal hyperplasia.

Neurologic findings – Hypotonia with poor sucking may accompany congenital or acquired neuromuscular weakness, prematurity with intraventricular hemorrhage, sepsis, malnutrition, and failure to thrive.

Ancillary studies — Laboratory testing and diagnostic imaging should be prompted by specific findings in the history and physical examination and the suspected diagnosis.

Laboratory studies that may be initially warranted include (see selected conditions above):

Complete blood count with differential

Serum electrolytes

Blood urea nitrogen and serum creatinine

Total and direct serum bilirubin

Rapid blood or serum glucose

Venous or arterial blood gas

Blood ammonia

Serum lactate

Urinalysis

Cultures of blood, urine, stool, and/or cerebrospinal fluid

Additional studies might include:

Electrocardiogram and echocardiogram to identify structural cardiac anomalies

Chest radiograph to evaluated for pneumonia or bronchopulmonary dysplasia

Abdominal ultrasound or upper gastrointestinal contrast series to identify pyloric stenosis or intestinal malrotation

Skeletal survey in victims of child neglect

Specialized testing(blood and urine studies) to identify inborn errors of metabolism (table 4 and table 5), congenital adrenal hyperplasia, or congenital chronic diarrhea (see "Clinical manifestations and diagnosis of classic congenital adrenal hyperplasia due to 21-hydroxylase deficiency in infants and children", section on 'Additional testing for infants with equivocal results')

SUMMARY AND RECOMMENDATIONS

Diagnostic approach – Weight loss in young infants is an important finding that may arise from a variety of conditions (table 1). A careful, thorough history and physical examination in conjunction with the judicious use of laboratory tests will often reveal the cause. The diagnostic approach to weight loss in the infant six months of age and younger is summarized in the algorithm (algorithm 1). (See 'Differential diagnosis' above and 'Approach' above.)

Red flag history – Rapid weight loss over a few days in a young infant is more indicative of a life-threatening process and needs prompt evaluation and treatment. Important historical features that suggest specific etiologies include (see 'Life-threatening conditions' above):

Bilious vomiting (see 'Intermittent intestinal malrotation' above)

Tachypnea, diaphoresis, or cyanosis with feeding (see 'Congenital heart disease' above)

History of ambiguous genitalia in a female infant or a positive screen for congenital adrenal hyperplasia (see 'Congenital adrenal hyperplasia' above)

Acute decompensation in the neonatal period with lethargy, vomiting, seizures, and/or abnormal odors (see 'Inborn error of metabolism' above)

History of fever, feeding difficulty, vomiting, and/or diarrhea with decreased urine output suggesting dehydration. Of note, severe symptoms from common conditions, such as acute infection (eg, gastroenteritis, urinary tract infection, pneumonia), pyloric stenosis, or feeding disorder may cause significant dehydration. (See 'Common conditions' above.)

Other important history – Young infants beyond the first week of life with weight loss persisting over one to two weeks warrant a careful feeding history. Specific etiologies are suggested by the following historical findings:

Prematurity, bronchopulmonary dysplasia, neuromuscular disease (eg, cerebral palsy or weakness), or anatomic malformations (eg, cleft lip and palate) causing difficulty with feeding (see 'Feeding disorder' above and 'Other conditions' above)

Symptoms of gastroesophageal reflux disease including feeding refusal, irritability with feedings, hematemesis, or arching and turning of the head (Sandifer syndrome) in association with frequent regurgitation while eating (see 'Gastroesophageal reflux disease' above)

Postprandial, nonbilious, often forceful vomiting occurring around four weeks of age and associated with demands for re-feeding soon after emesis ("hungry vomiter") in infants with pyloric stenosis (see 'Pyloric stenosis' above)

Poverty associated with inadequate breastfeeding or supply of formula (see 'Malnutrition and failure to thrive' above)

Drug use in one or both caregivers, prior placement of siblings into foster care, and poor compliance with recommended medical care suggesting child abuse and neglect

Vomiting, diarrhea, abdominal distension, and/or blood stools starting within days or weeks after the introduction of a cow's milk-based formula or in breastfeeding infants in whom the mother ingests cow's milk (see 'Milk protein allergy' above)

Oliguria or anuria in a newborn infant indicating acute kidney injury

Frequent, recurrent infections suggesting primary immunodeficiency or human immunodeficiency virus (HIV) infection (see 'Other conditions' above)

Chronic diarrhea since birth consistent with congenital chronic diarrhea (see 'Other conditions' above)

Physical examination – During physical examination, the weight should be obtained and compared with prior measurements along with length and head circumference. These measurements should be plotted on the appropriate growth chart and compared with any previously available measurements to assess for rate of loss and changes in weight percentile (see "Normal growth patterns in infants and prepubertal children", section on 'Growth charts'). Failure of adequate growth in head circumference in association with weight loss is of particular concern in young infants. (See 'Physical examination' above.)

Direct observation of the infant feeding frequently provides important information regarding the cause of weight loss. Any accompanying respiratory distress, sweating, or choking with feeds should be noted as they may be associated with an underlying cause of poor weight gain. Additionally, any difficulty with breastfeeding, infant latch, painful nipples, or mastitis should be noted. (See 'Physical examination' above.)

Ancillary studies – Laboratory testing and diagnostic imaging should be prompted by specific findings in the history and physical examination and the suspected diagnosis. (See 'Ancillary studies' above.)

Topic 82899 Version 15.0

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