Meralgia paresthetica (lateral femoral cutaneous nerve entrapment)

INTRODUCTION — Meralgia paresthetica (from "meros," meaning thigh, and "algo," meaning pain) is the clinical syndrome of pain and/or dysesthesia in the anterolateral thigh associated with compression of the lateral femoral cutaneous nerve. The lateral femoral cutaneous nerve is a pure sensory nerve that is susceptible to compression as it courses from the lumbar plexus, through the abdominal cavity, under the inguinal ligament, and into the subcutaneous tissue of the thigh.

The causes, presentation, diagnosis, and treatment of meralgia paresthetica are reviewed here. Other mononeuropathies of the lower extremities are reviewed separately. (See "Overview of lower extremity peripheral nerve syndromes".)

CAUSES AND RISK FACTORS — Most cases of meralgia paresthetica arise spontaneously and are presumed to result from entrapment of the lateral femoral cutaneous nerve as it passes underneath or through the inguinal ligament (figure 1). The most commonly identified risk factors are obesity, diabetes mellitus, and older age [1,2]. The median age at presentation is 50 years. The incidence is approximately sevenfold higher in patients with diabetes compared with the general population [1].

A more specific cause is identified in approximately one-third to one-half of patients [1,2]. Examples related to compression at the inguinal ligament include:

●Body habitus (eg, large abdomen with overlying panniculus) [3]

●Pregnancy [4-6]

●Increased intraabdominal pressure due to ascites

●Tight belts or waistbands [7-9]

●Compression from a wallet

●Prolonged leaning of a thigh against a bench or table

●Carrying heavy objects supported by the thigh or groin

●Long-distance walking, cycling, or circuit training, possibly related to local ischemia during repetitive muscle stretching [10,11]

●Groin trauma, such as a seat belt injury in a motor vehicle crash [12]

Postoperative meralgia paresthetica can result from injury during local or regional surgeries, including [8,13]:

●Spine procedures

●Iliac crest bone harvesting

●Hip prosthesis

●Aorto-bifemoral bypass

●External compression from prolonged lithotomy position

●Direct injury from laparoscopic inguinal herniorrhaphy

●Compression from a retractor during gastroplasty for obesity

The nerve is occasionally affected proximal to the inguinal ligament in the pelvis by retroperitoneal tumors or hematomas. In this location, however, isolated involvement of the lateral femoral cutaneous nerve is relatively unusual. Pelvic tumors and hematomas more commonly cause both sensory and motor abnormalities due to involvement of the femoral nerve or lumbosacral plexus. (See 'Differential diagnosis' below.)

ANATOMY — The lateral femoral cutaneous nerve branches off of the lumbar plexus and conveys fibers from the L2 and L3 nerve roots (figure 2). The nerve courses through the pelvis, running adjacent to the lateral edge of the psoas muscle. It enters the leg underneath or through the inguinal ligament, medial to the anterior superior iliac spine (figure 1); it is in this location that entrapment can occur. The nerve is purely sensory, relaying sensory information from the anterolateral and lateral thigh.

Anatomic variations exist. A cadaveric study showed that the nerve could course anywhere from 6.5 cm medial to the anterior superior iliac spine to 6 cm lateral to it [14]. This is important from the standpoint of local injection. (See 'Persistent symptoms' below.)

CLINICAL FEATURES

Signs and symptoms — Meralgia paresthetica is characterized by pain, paresthesia (numbness and tingling), and hypesthesia (diminished sensation) over the upper outer thigh. Symptoms are usually unilateral. The onset of pain is typically subacute.

Patients characterize their symptoms as burning, stinging, or "pins and needles" sensations, superficially in the skin. Itching may also be present. They may complain of hyperpathia, in which light touch (from clothing or a hand) results in unpleasant sensations. Some studies report that pain tends to be unchanged with positional changes or activities including walking or standing [1], while others report that pain can be aggravated by thigh extension or prolonged walking or standing and relieved by sitting [15]. In some cases, discomfort is exacerbated by Valsalva maneuvers or other activity that increases intraabdominal pressure.

Clinical examination shows a loss of light touch and/or pinprick sensation in a discrete area of the upper lateral thigh, often in a more restricted area than the zone of paresthesias. Symptoms may be reproduced by tapping over the lateral aspect of the inguinal ligament (Tinel's sign). Neurologic findings are restricted to sensory changes, since the lateral femoral cutaneous nerve does not contain motor fibers.

Electrodiagnostic findings — Sensory nerve conduction studies (NCS) of the lateral femoral cutaneous nerve are technically difficult, and side-to-side comparisons are essential. NCS are supportive of meralgia paresthetica if the lateral femoral cutaneous sensory response in the affected leg is unilaterally absent or reduced in comparison with the asymptomatic leg [8,16-19]. The needle electromyography (EMG) study is normal.

Sensitivity and specificity of NCS in meralgia paresthetica are not well studied. In practice, sensory responses are variable and difficult to obtain in overweight or older adults. A study using a specialized technique of inguinal segmental and distal sensory NCS in 34 patients with meralgia paresthetica reported absent lateral femoral cutaneous sensory responses in 32 percent of patients and delayed conduction across the inguinal ligament in 45 percent of patients [20].

EVALUATION

History — Patients with suspected meralgia paresthetica should be asked about recent weight gain, use of tight-fitting clothes or belts, exercise habits, and other potential risk factors for compression at the inguinal ligament. A specific cause or provocative factor can be identified in up to half of patients. (See 'Causes and risk factors' above.)

Probing for exacerbating and mitigating factors is of variable utility, but exacerbation of symptoms with Valsalva or prolonged walking is helpful in suggesting inguinal compression. Pain, if present, should be limited to the anterolateral thigh. Back pain, including radicular pain or "sciatica," should raise suspicion for lumbosacral spine or plexus pathology rather than meralgia paresthetica. (See 'Differential diagnosis' below.)

Neurologic examination — A focused neurologic examination of the lower extremities should be performed in all patients to detect diminished sensation in the distribution of the lateral femoral cutaneous nerve and to rule out weakness or reflex changes suggesting an alternative diagnosis.

●Sensory examination – Pinprick and light touch should be tested in the affected thigh. Hypesthesia is typically present in a 10 x 6 inch oval-shaped area on the anterolateral thigh (figure 1). However, the distribution of the lateral femoral cutaneous nerve is not strictly lateral; thus, abnormalities are occasionally also seen on the anterior thigh. The sensory examination is otherwise normal, although patients with diabetes may have sensory loss in a distal symmetric distribution, suggestive of a distal symmetric polyneuropathy. (See "Screening for diabetic polyneuropathy", section on 'Clinical manifestations'.)

●Motor examination – The motor examination should include bilateral muscle strength testing of all major muscle groups (ie, hip flexion and extension, thigh abduction and adduction, knee flexion and extension, ankle dorsi- and plantarflexion, foot inversion and eversion, and toe flexion and extension) and straight leg raise. The straight leg raise is negative, and proximal and distal motor strength is preserved.

●Reflexes – Deep tendon reflexes in the legs should be symmetric. Loss of the patellar or Achilles reflex on the side of the sensory abnormality suggests an alternative diagnosis (eg, L3/L4 radiculopathy, femoral neuropathy). (See 'Differential diagnosis' below.)

Additional testing in selected patients

●Imaging – Imaging of the spine and/or pelvis is generally not necessary if the history and examination findings are characteristic for meralgia paresthetica. Patients with atypical signs or symptoms or an unreliable examination should be imaged to rule out alternative diagnoses.

Magnetic resonance imaging (MRI) of the lumbosacral spine is the best study to assess for structural lumbosacral spine disease if there is clinical suspicion for an L3/L4 radiculopathy. A pelvic MRI or computed tomography (CT) is appropriate if a lumbar plexopathy is being considered in order to look for tumor or hemorrhage. (See 'Differential diagnosis' below.)

●Nerve conduction studies (NCS)/electromyography (EMG) – Most patients with typical signs and symptoms of meralgia paresthetica do not require NCS/EMG. The role of NCS/EMG is primarily to exclude an L3/L4 radiculopathy, lumbar plexopathy, or femoral neuropathy in patients with atypical clinical presentations. (See 'Differential diagnosis' below.)

When present, absent or reduced sensory responses in the lateral femoral cutaneous nerve and delayed conduction across the inguinal ligament are supportive of meralgia paresthetica. (See 'Electrodiagnostic findings' above.)

DIAGNOSIS — Meralgia paresthetica should be suspected in patients with pain, paresthesia, and/or numbness in the upper outer thigh, particularly in the presence of risk factors such as obesity and diabetes. Meralgia paresthetica is a clinical diagnosis based primarily upon all of the following features:

●Pain, paresthesia, and numbness in the lateral or anterolateral thigh (see 'Clinical features' above)

●Sensory abnormalities (eg, decreased pinprick) in the distribution of the lateral femoral cutaneous nerve (figure 1)

●Absence of other neurologic abnormalities of the leg (eg, weakness, loss of knee reflex)

DIFFERENTIAL DIAGNOSIS — The differential diagnosis of meralgia paresthetica consists of other peripheral nervous system lesions that supply overlapping sensory territory in the anterior and lateral thigh. Anatomically, this includes lumbar (L3/L4) radiculopathy, lumbar plexopathy, and femoral neuropathy. These alternate conditions usually produce weakness of hip flexion and/or knee extension, atrophy of the thigh muscles, and loss of the knee reflex, all findings that are absent in meralgia paresthetica.

●L3/L4 radiculopathy – The anterolateral thigh corresponds primarily to the L3 and L4 dermatomes (figure 3). Muscular innervation of the anterior thigh is overlapping, and involvement of either level may produce weakness of hip flexion, knee extension, and hip adduction (table 1). Radiculopathies secondary to nerve root compression typically involve back pain with radiation into the thigh and occasionally below the knee down the medial aspect of the leg. Pain may be reproduced on straight leg raise testing and exacerbated by back movement, coughing, sneezing, or straining. The most common causes of L3/L4 radiculopathy are nerve root compression due to disc herniation and spondylosis. (See "Acute lumbosacral radiculopathy: Etiology, clinical features, and diagnosis", section on 'Clinical presentations'.)

●Lumbosacral plexopathy – The lumbar plexus is derived from the anterior rami of the L1 through L4 nerve roots and runs along the psoas major muscle in the pelvis (figure 2). Lumbar plexus lesions tend to cause weakness of hip flexion and adduction and/or knee extension. Sensory disturbances usually involve the anterior and medial thigh. The most common causes are diabetic amyotrophy, idiopathic lumbosacral radiculoplexus neuropathy, retroperitoneal or pelvic tumors, and retroperitoneal hematomas. (See "Lumbosacral plexus syndromes".)

●Femoral neuropathy – The femoral nerve is the largest nerve emerging from the lumbar plexus. It passes under the inguinal ligament medial to the lateral femoral cutaneous nerve of the thigh. The femoral nerve innervates the anteromedial skin of the thigh (via the medial femoral cutaneous branch) as well as medial lower leg via the saphenous nerve (figure 4 and figure 5). Weakness typically involves the quadriceps muscle group (knee extension) with sparing of adduction and variable involvement of hip flexion. The knee jerk reflex is usually lost. Common causes include iatrogenic surgical injury, hip or pelvic fractures, and masses or hematomas within the iliacus muscle. (See "Overview of lower extremity peripheral nerve syndromes", section on 'Femoral nerve'.)

Electrodiagnostic studies can assist in the differential diagnosis and guide the need for imaging of the lumbar spine or pelvis. The needle electromyography (EMG) study is normal in meralgia but abnormal in characteristic patterns in radiculopathies, plexopathies, and femoral neuropathies. Relevant findings supporting an alternative diagnosis may include evidence of acute or chronic nerve injury in the vastus lateralis, vastus medialis, and iliopsoas muscles (for femoral neuropathies, lumbar plexopathies, or lumbar radiculopathies) and adductor brevis and longus muscles (for lumbar plexopathies or L3/L4 radiculopathies). (See "Overview of lower extremity peripheral nerve syndromes", section on 'Diagnostic testing'.)

TREATMENT

Initial therapy — Meralgia paresthetica is a self-limited, benign disease in most patients. Spontaneous remission is frequent [1]. More than 90 percent of patients respond to conservative measures alone, although recurrent symptoms are common [21,22].

The acute therapy of meralgia paresthetica includes the following:

●Educate and reassure the patient that the disorder does not represent a serious back problem and usually resolves spontaneously.

●Recommend ways to reduce pressure over the nerve in the groin area, such as avoiding tight garments and belts.

●Discuss the need for weight loss if appropriate.

Some patients find symptomatic relief with as-needed use of oral nonopioid analgesics. Physical therapy does not play a significant role in the management of this disorder. Abdominal toning exercises may reduce pressure over the nerve but are of unproven value.

Persistent symptoms — In patients with persistent symptoms for more than one to two months, despite the above measures, reexamine the dysesthetic area to confirm the local nature of the problem. (See 'Differential diagnosis' above.)

Anticonvulsants such as carbamazepine, phenytoin, or gabapentin may be helpful in reducing neuropathic pain symptoms but have not been systematically studied in meralgia paresthetica. (See "Pharmacologic management of chronic non-cancer pain in adults", section on 'Antiseizure medications'.)

Consultation with an anesthesiologist for a local nerve block can also be considered for persistent symptoms. Injection of a local anesthetic agent, glucocorticoid, or both can be useful to temporarily treat this neuropathy [23-25].

Rarely, surgery is necessary in patients with severe chronic symptoms that are refractory to more conservative measures [26].

●Surgical release – Decompression of the nerve (sectioning the inferior slip of the attachment of the inguinal ligament to the anterior superior iliac spine) may provide long-lasting relief in some patients. This procedure has the advantage of preserving sensory function. However, it is not uniformly successful.

●Nerve transection – Sectioning of the lateral femoral cutaneous nerve as it exits the pelvis is the most definitive procedure but has the disadvantage of permanent anesthesia [21]. From a practical point of view, only patients with intractable dysesthetic pain are willing to undergo a procedure that results in permanent anesthesia.

Supporting evidence for surgery includes a retrospective series of 167 patients with meralgia paresthetica who had surgical release (n = 153) or transection (n = 14) [27]. At a mean follow-up of 98 months, symptomatic improvement and patient satisfaction were observed in 130 (78 percent). In a prospective series of 22 surgically treated patients (8 with neurolysis and 14 with neurectomy), pain reduction was reported in 93 percent of those who underwent neurectomy as compared with 38 percent of those with neurolysis, suggesting that neurectomy may be more effective [28]. Numbers were small, however, and a randomized controlled trial was recommended. A subsequent literature review concluded that there was insufficient evidence to recommend one treatment over the other [29].

In a few case reports, patients with refractory symptoms noted improvement after pulsed radiofrequency nerve ablation of the lateral femoral cutaneous nerve [30-33]. Further data are needed to determine the benefit of this procedure for treating meralgia paresthetica.

SUMMARY AND RECOMMENDATIONS

●Definition – Meralgia paresthetica is the term used to describe the clinical syndrome of pain, dysesthesia, or both in the anterolateral thigh associated with compression of the lateral femoral cutaneous nerve (figure 1). (See 'Introduction' above.)

●Etiology and risk factors – Most cases of meralgia paresthetica are due to entrapment of the lateral femoral cutaneous nerve as it passes underneath or through the inguinal ligament (figure 1). The most common risk factors are obesity, diabetes mellitus, and older age. It can also occur as a surgical complication and be due to restrictive clothing, body habitus, or other factors that result in local compression of the nerve at the inguinal ligament. (See 'Anatomy' above and 'Causes and risk factors' above.)

●Clinical features – Meralgia paresthetica is characterized by unilateral pain, paresthesia (numbness and tingling), and hypesthesia (diminished sensation) over the upper outer thigh. Patients characterize their symptoms as burning, stinging, or "pins and needles" sensations, superficially in the skin. Clinical examination shows a loss of light touch and/or pinprick sensation in a discrete area of the upper lateral thigh. (See 'Clinical features' above.)

●Diagnosis – The diagnosis of meralgia paresthetica is based primarily upon the unique description of pain and paresthesias in the characteristic location, sensory abnormalities on examination, and the absence of other neurologic abnormalities such as weakness or reflex changes. (See 'Evaluation' above and 'Diagnosis' above.)

●Differential diagnosis – The differential diagnosis consists of other peripheral nervous system lesions that supply overlapping sensory territory in the anterior and lateral thigh, including lumbar (L3/L4) radiculopathy, lumbar plexopathy, and femoral neuropathy. (See 'Differential diagnosis' above.)

●Initial conservative therapy – Meralgia paresthetica is a self-limited, benign disease in most patients. More than 90 percent of patients respond to conservative measures alone, although recurrent symptoms are common. (See 'Initial therapy' above.)

●Treatment options for persisting symptoms – For patients with symptoms that persist for more than one to two months despite conservative measures, anticonvulsants such as carbamazepine, phenytoin, or gabapentin can be helpful in reducing neuropathic pain. A local nerve block can also be considered. Rarely, surgical nerve decompression or sectioning is necessary. (See 'Persistent symptoms' above.)

ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Bruce C Anderson, MD, who contributed to an earlier version of this topic review.