Surgery for Meralgia Paresthetica 

Updated: May 31, 2017
Author: Ira Kornbluth, MD, MA, FAAPMR; Chief Editor: William L Jaffe, MD 

Overview

Background

Meralgia paresthetica is a common but underrecognized condition that is manifested by pain, numbness, and tingling in the anterior and lateral parts of the thigh. Bernhardt first described symptoms corresponding to meralgia paresthetica in 1878. In 1885, Hagar correctly suggested that compression of the lateral femoral cutaneous nerve (LFCN) was the source of this symptom complex; surgical correction of meralgia paresthetica also dates back to Hagar.  A decade later, Roth coined the term meralgia paresthetica from the Greek words meros (thigh) and algos (pain). Anecdotally, Sigmund Freud is said to have diagnosed himself and his son with this condition.

Entrapment of the LFCN results in pain and sensory abnormalities in the anterolateral thigh. This nerve is a pure sensory nerve that typically receives its innervation from the L2-3 lumbar nerve roots and includes sudomotor fibers. Sudomotor changes, such as mild sweating in the nerve distribution, may be evident, although this is uncommon. Because the LFCN is purely sensory, no associated motor or reflex findings should be present.[1, 2]

As physicians and patients become increasingly aware of meralgia paresthetica and as new medications and surgical techniques develop, the diagnosis and initiation of a treatment plan will be made more rapidly. Patients and physicians alike would benefit from an algorithm guiding diagnosis and treatment.

Anatomy

The LFCN typically arises from lumbar nerve roots, specifically those at the L2-3 levels, though it can arise from different combinations of the L1-3 nerve roots. The LFCN pierces the psoas, travels across the iliacus toward the anterior superior iliac spine (ASIS), and then enters the anterolateral thigh by passing under, through, or above the inguinal ligament. (See the image below.) It is surrounded by a fascial canal.[3]

The lateral femoral cutaneous nerve provides senso The lateral femoral cutaneous nerve provides sensory innervation to the anterolateral thigh. Courtesy of Essentials of Physical Medicine and Rehabilitation, Hanley & Belfus Publishers, 2001, used with permission.

In most individuals, the LFCN crosses into the anterolateral thigh approximately 1 cm medial to the ASIS. However, the relation of the LFCN to the ASIS is quite variable.[3] The nerve may cross into the anterolateral thigh as much as 2 cm lateral or 6 cm medial to the ASIS. A bifurcation into anterior and posterior divisions occurs approximately 5-12 cm below the ASIS.

Cadaver dissections have demonstrated that anatomic variations are also found in the origin of the LFCN. As many as 30% of LFCNs may be derived partially or entirely from adjacent genitofemoral or femoral nerves.

Pathophysiology

Along its course, the LFCN is vulnerable to compression at several sites. The nerve emerges from the psoas muscle, intersects with the inguinal ligament, curves around the ASIS, and exits from the fascia lata. Meralgia paresthetica most commonly occurs from compression of the nerve as it exits the pelvis.[4, 5]

Peripheral nerve injuries are described in terms of the nature of the insult and the associated prognosis. Thus, a compressive force results in a neurapraxic injury to the nerve, which is characterized by the loss of myelin without affecting the axon or its axonal sheath. Neurapraxic injuries have the best prognosis and may heal over hours to months, depending on the severity. Loss of the axon or its axonal sheath constitutes a more severe nerve injury and a worse prognosis for healing, because the nerve undergoes wallerian degeneration or destruction of the nerve fibers distal to the injury site.[6]

If the injury involves only the axons and spares the axonal sheath (axonotmesis), the patient may make a full, but likely slow, recovery. If the axonal sheath is affected such that the nerve is in discontinuity (neurotmesis), then the prognosis for spontaneous recovery is poor. Most commonly, compressive forces tend to result in neurapraxic injuries, and relief of the compressive force initiates the healing process.

Etiology

Metabolic conditions, such as diabetes, alcoholism, and thyroid disorders, can contribute to the development of a neuropathy in the LFCN and other peripheral nerves. In most instances, the etiology of meralgia paresthetica involves excessive pressure on the nerve at various sites of possible entrapment. Pressure may be from internal causes such as obesity, pregnancy, or pelvic tumors.

There is a higher incidence of obesity in patients with meralgia paresthetica, which strongly suggests that obesity is an independent risk factor.[7] Alternatively, external causes such as tight belts worn around the waist may be identified as the culprit.[8, 9] In addition, the LFCN may be injured iatrogenically from local trauma during surgical procedures. Hip replacement, iliac crest bone grafting, appendectomy, inguinal lymph node dissection, aortofemoral bypass, uterine surgery, cesarean section, and quadriceps surgery have all been implicated as causative for meralgia paresthetica.

Epidemiology

The prevalence of meralgia paresthetica has been estimated at 3 cases per 10,000 individuals, and this condition has been reported in up to 35% of patients referred for evaluation of leg discomfort. However, these symptoms are often not recognized or they may be mistaken for other conditions such as lumbar radiculopathy. In a large case series,[10] the presumptive diagnosis by the referring physician was meralgia paresthetica in 47 of 120 patients (39%).

This condition has been described in toddlers and elderly persons, but most cases occur in patients aged 30-65 years. Whether a sex predominance exists is unclear. Meralgia paresthetica is usually unilateral but may be bilateral in as many as 50% of cases.

Prognosis

The outcome of meralgia paresthetica depends largely on whether the diagnosis and treatment plan are achieved within a reasonable time frame. The prognosis from conservative management alone is quite good because the condition often is self-limited. In 277 patients treated conservatively by Williams et al, 91% had satisfactory symptom relief.[11] In the worst-case scenario, patients treated conservatively had persistent symptoms such as pain, numbness, burning, hyposensitivity, and tingling in the anterolateral thigh.

Controversial issues include the efficacy of surgery and the selection of a surgical procedure. van Eerten et al[12] noted complete symptom relief in three of 10 patients who underwent neurolysis and in nine of 11 patients who had a transection. Similarly, 23 of 24 patients who had a transection in Williams and Trzil's series had complete relief of their presenting symptoms.

Ivins reported results for eight patients who underwent neurolysis; four experienced relief of symptoms, of whom two had recurrence of their symptoms.[13] Siu and Chandran reported results from a case series of 45 decompressive procedures in 42 patients who underwent neurolysis: 43% reported complete relief, 40% reported partial relief, and 17% reported no relief.[14]

Although transection is more likely to produce complete relief, it likely will cause permanent anesthesia of the anterolateral thigh.

 

Presentation

History and Physical Examination

A thorough medical and surgical history is important for the correct diagnosis of meralgia paresthetica, including questioning the patient about the possibility of any relevant trauma.[15, 16, 17]

The physical examination in patients with meralgia paresthetica is remarkable for the findings of altered sensation in the anterolateral thigh, including pain, numbness, burning, hyposensitivity, and tingling. Typically, the symptoms begin insidiously and do not extend below the knee. The pain tends to be sharp or burning but also may be dull or achy.

The examiner should also consider whether any abnormal postures or movements are contributing to the patient's symptoms. Prolonged standing and standing up from a seated position may aggravate the condition.

Motor and reflex examination findings should be normal. If the patient has evidence of motor weakness or low back pain, other diagnoses should be considered because the lateral femoral cutaneous nerve (LFCN) is purely sensory, and a neurologic examination should be conducted.

Trigger points, lumbar radiculopathy, plexopathy, and hip pathology can masquerade as meralgia paresthetica. A positive Tinel sign finding may be elicited near the anterior superior iliac spine (ASIS).

Meralgia paresthetica may affect a very large region of the anterior and lateral thigh. However, the involved area can vary significantly, depending on the site of entrapment and anatomic variations of the nerve. In a large case series[10] of 120 patients, 88 (73%) had symptoms solely in the lateral aspect of the distal thigh. In 11 of the 120 patients (9.2%), the anterior aspect of the thigh was exclusively involved.

 

Workup

Laboratory Studies

Laboratory evaluation for diabetes and thyroid disorders may be warranted in some cases. Although meralgia paresthetica is not an obscure condition, the diagnosis may be elusive because it is based largely on clinical grounds.

Imaging Studies

Imaging studies generally are not of any specific benefit in diagnosing meralgia paresthetica, except in excluding differential diagnoses. If a mass lesion or fracture is suspected as the cause of this entity, appropriate imaging may be warranted.

A study by Suh et al found ultrasonography to be useful as a supplemental diagnostic tool for meralgia paresthetica that could provide information about the morphology and course of the lateral femoral cutaneous nerve (LFCN).[18]  A study by Hanna et al found preoperative ultrasound-guided wire localization to be useful for minimizing the time needed to find the LFCN, as well as for identifying anatomic abnormalities that might not be apparent otherwise.[19]

A small study by Chhabra et al found 3-Tesla magnetic resonance neurography to be reliable and accurate for the diagnostic evaluation of meralgia paresthetica.[20]

Electrodiagnostic Evaluation

An electrodiagnostic evaluation, including electromyography (EMG) and nerve conduction studies, is often unnecessary but may be helpful as an adjunct to the history and physical examination in confirming the diagnosis of meralgia paresthetica and establishing a prognosis.

Nerve conduction tests can help determine the severity of the nerve injury by comparing the result with standard values and with the contralateral side. The smaller the amplitude relative to the contralateral side, the greater the nerve dysfunction. Frequently, recording needles are required for sensory testing to ensure adequate responses. If very low amplitudes are obtained, an average of responses may be used.

Comparing nerve conduction study findings on the affected side with those from the contralateral side provides some indication of the nature and severity of the nerve injury. Studies may be confounded by the fact that many patients have bilateral involvement. The LFCN can be stimulated as it exits the pelvis, with potentials recorded distally, or it can be stimulated distally, with recordings made proximally. Ultrasound-guided nerve conduction study of the LFCN has been described.[21]

Needle EMG testing may be performed to evaluate for other pathologic conditions, such as radiculopathy or other peripheral neuropathies. In meralgia paresthetica, needle EMG findings should be normal.

Somatosensory evoked potentials have been found to be less accurate than nerve conduction studies.

 

Treatment

Approach Considerations

Treatment for meralgia paresthetica is directed toward identification and relief of the compressive force on the lateral femoral cutaneous nerve (LFCN). In many instances, the nerve spontaneously heals if the compression is relieved. If symptoms continue, anti-inflammatory medications, local injection, and other nonsurgical modalities can be considered. If these methods fail, surgery may be an option.

No absolute contraindications are recognized for LFCN surgery. Relative contraindications include any comorbidities that place the patient at increased general surgical risk.

Meralgia paresthetica is a benign condition; in conservatively treated patients, complications are limited to persistent symptoms despite treatment. No weakness or disabling features should occur from this entity.

Medical Therapy

Devising a strategy to identify and relieve the compressive force should be the first step in the treatment of meralgia paresthetica. For example, a tool belt or tight clothing could induce or exacerbate symptoms. In obese patients, weight loss alone may prove to be very beneficial. Patients should be advised to avoid prolonged sitting because this may increase pressure on the LFCN. Abnormal postures and movements should be addressed. Modalities such as heat, ice, and electrical stimulation can be used for symptomatic relief as appropriate.

Use of nonsteroidal anti-inflammatory drugs (NSAIDs), tricyclic antidepressants (TCAs; eg, amitriptyline), and anticonvulsant agents (eg, gabapentin) may be helpful in providing some degree of symptomatic relief. NSAIDs have the potential to cause gastrointestinal ulcerations, damage renal and liver function, and exacerbate hypertension. Anticonvulsant medications can precipitate seizures, cause excess fatigue, or induce weight gain. Common effects of TCAs are dry mouth and urinary retention

Alternatively, local injections using steroid and local anesthetic preparations may reduce symptoms by decreasing any inflammatory component and disrupting the pain circuit.[22, 23] Long-term neurotoxic agents (eg, phenol) are not recommended, because of the possibility of adverse effects (eg, dysesthesias).

In most instances, the injection is performed just inferior to the inguinal ligament and 1 cm medial to the anterior superior iliac spine (ASIS). However, the physician should recognize that the nerve pathway can vary significantly and should therefore adjust the location of the injection accordingly. Ultrasonography can be helpful for guiding injection therapy.[24]

Surgical Therapy

In cases resistant to conservative measures, surgical options may be considered. The decision to pursue surgery depends on the extent and nature of the symptoms. Neurolysis alone, neurolysis with transposition of the nerve, and transection of the nerve are the most commonly performed surgical procedures for meralgia paresthetica.

A prospective observational study by de Ruiter et al suggested that neurectomy may achieve better pain relief than neurolysis does,[25] but further study is required to investigate this issue in greater depth. A subsequent review by Payne et al concluded that there was not yet sufficient evidence to recommend either of these treatment methods over the other.[26]

Before the procedure, the patient should be counseled about the potential risks and outcomes to be expected (see Complications).

Surgery may be performed with the patient under local or general anesthesia.

A small incision is made just distal to the site where the LFCN intersects the inguinal ligament. The nerve is exposed, and any compressive force is identified. The surgical procedure (neurolysis alone, neurolysis with transposition, or transection) is then performed. Which of these procedures is most effective and which should be attempted first are topics of some debate.[27]

Commonly, neurolysis or neurolysis with transposition is considered prior to transection because transection results in permanent numbness in the nerve distribution. Transection may be the only option if the nerve has been severely damaged or if multiple branches are affected. On the other hand, the rate of symptom recurrence may be higher with the neurolytic procedures than with transection. In transections, the surgeon should ensure that the proximal portion of the nerve is within the pelvis to minimize the formation of a painful neuroma.

Complete lysis is achieved by freeing the nerve at the tendinous arc from the iliac fascia; anteriorly, at the inguinal ligament; posteriorly, at a sling of fascia; and, distally, at the deep fascia of the thigh along each division.

Complications

Surgical complications include the following:

  • Infection
  • Excess bleeding
  • Failure to relieve symptoms
  • Worsening of pain

In addition, permanent anesthesia of the anterolateral thigh is an expected consequence of transection, and neuromas may develop.

Long-Term Monitoring

Some surgical site tenderness is expected for a few days and can be managed with analgesics. Range of motion and function should not be restricted after surgery.

The patient should have thorough neurologic examinations immediately after the procedure and serial examinations for several months afterward to evaluate whether the procedure helped alleviate the symptoms of meralgia paresthetica and to identify any complications.