Physical Medicine and Rehabilitation for Meralgia Paresthetica

The lateral femoral cutaneous nerve (LFCN) is formed by the fusion of the posterior branches of the second and third lumbar nerves. This purely sensory nerve traverses the retroperitoneum around the lateral circumference of the ileum to the inguinal ligament (IL). Just medial to the anterosuperior iliac spine (ASIS), the LFCN passes underneath the IL and enters the anterior thigh beneath its fascia (see the image below). Ordinarily, a few centimeters distal to the IL, the LFCN divides into anterior and posterior branches. Tributaries of these branches perforate thigh fascia and receive sensory information from portions of the associated dermatomes L2-L3. Typically, this area encompasses the anterior lateral thigh from just below the hip to above the knee. Variations in the anatomy of the LFCN, such as splitting by the inguinal ligament, are hypothesized to predispose it to neuropathic processes.[9, 10, 11]

Basic anatomy of the lateral femoral cutaneous sensory nerve. The blue region over the anterolateral thigh outlines the area of cutaneous innervation.

A study by Moritz et al found the LFCN to be closer to the ASIS in patients with idiopathic MP than it was in controls. Using high-resolution ultrasonography, the investigators determined that among the study’s 28 patients with MP, the mean distance of the LFCN from the ASIS was 0.52 cm, compared with 1.79 cm in the 15 controls.[12]

Nerve entrapment can occur at 3 potential sites, including (1) beside the spinal column, (2) within the abdominal cavity as the nerve courses along the pelvis, and (3) as the nerve exits the pelvis. The last site is the most common; there, nerve entrapment may involve the sartorius muscle, or it may be caused by simple compression superficially near the iliac crest and ASIS by tight clothing or trauma.

The angulation of the LFCN across the iliac crest results in varying compressive forces with postural repositioning. One opinion is that fibrous bands within the fascia subject the LFCN to deleterious tensile forces. The relatively superficial trajectory of the LFCN as it enters the thigh compartment makes it extremely prone to injury due to compression against underlying bone.

The LFCN is subject to systemic processes that can detrimentally affect any peripheral nerve. Diabetes mellitus, for example, can result in diffuse or focal neuropathies, especially in nerves, such as the LFCN, that are subject to excessive compressive forces.

Movement of the hip changes angulation and tension of the nerve, which can affect symptoms. For example, hip extension may increase angulation and tension on the LFCN, and flexion can decrease these forces.

A Brazilian study involving 14 patients with meralgia paresthetica (MP) and 14 control subjects found evidence that not only are the large myelinated nerve fibers of the LFCN affected in MP, but the small fibers may be as well, with the small fibers suffering a partial loss of function and causing painful symptoms.[13] The investigators suggested that this is particularly true in individuals who have had MP for a longer period of time.

Frequency

United States

Considered uncommon but not rare, meralgia paresthetica (MP) is probably underrecognized. Notably, 3 cases are reported per 10,000 general clinic patients. Also, it occurs in an estimated 7-35% of patients referred for leg discomfort. Up to 20% of patients with MP have bilateral symptoms.

Mortality/Morbidity

Isolated meralgia paresthetica (MP) secondary to compression or injury of the nerve unrelated to major trauma or to systemic or malignant processes is not associated with mortality or significant morbidity.

Sex

Meralgia paresthetica is more common in males than in females.

Age

Meralgia paresthetica is observed in all age groups, but the condition most commonly occurs in middle-aged adults.

A patient whose meralgia paresthetica (MP) is idiopathic or is caused by mechanical injury near the IL may describe paresthesias or dysesthesias within the cutaneous distribution of the lateral femoral cutaneous nerve (LFCN).

• Paresthesias are abnormal sensation perceptions, such as tingling, numbness, burning, itching, cold, and warmth, that are not triggered by obvious cutaneous physical stimulation.

• Dysesthesias are distorted perceptions of ordinary tactile or painful stimuli (eg, burning, tingling, itchiness).[10]

• Changes in posture or prolonged sitting or standing may cause a fluctuation of symptoms. The discomfort may resolve spontaneously and reappear.

• The appearance of MP symptoms may accompany other factors, such as a motor vehicle accident, pregnancy, surgery, weight loss, and weakness. The examiner should inquire about these associations, because LFCN pathology has several etiologies, some of which are benign and others of which require urgent investigation.

Isolated lesions of the lateral femoral cutaneous nerve (LFCN) result only in abnormalities on sensory examination. Reduced perception of pinprick or dysesthesia within the receptive fields of the LFCN is typical. Often, the clinician can plot the cutaneous boundaries of the LFCN with an ink marker on the thigh of a person with meralgia paresthetica (MP). A careful neurologic examination is necessary so that it is not assumed that the patient has a benign form of MP. Hip extension may elicit symptoms, while flexion may relieve them.

• If the neurologic examination reveals abnormalities in reflexes, power, gait, or sensation outside the boundaries of the LFCN, then processes concurrently affecting other nerves are considered. For example, reduced patellar reflex, weak leg extension, and symptoms of MP indicate possible pathology within the lumbar plexus, such as a space-occupying lesion. This condition is a plexopathy, not MP.

• Application of pressure over the LFCN at the IL may elicit tenderness or exacerbate the symptoms of MP. This Tinel sign supports localization of the pathologic process to that region.

Several processes can affect the lateral femoral cutaneous nerve (LFCN) detrimentally along its course, causing sensory dysfunction perceived within its cutaneous distribution.[14] The processes cited below cause classical meralgia paresthetica (MP; lesion of the LFCN at IL) and pathologies that produce symptoms of MP due to lesions at various points along the LFCN. In many of these diagnoses, additional neurologic symptoms, signs, and examination findings may be present that would indicate LFCN pathology along with other nerve injuries (eg, lumbar or lumbosacral plexopathy, multiple level radiculopathy).

• Trauma

  • Acute compression of the LFCN at the IL from seatbelt forces in rapid deceleration during motor vehicle accidents

  • Pelvic fracture

• Iatrogenic - LFCN injury has been reported in the following surgical procedures:

  • Iliac crest bone grafting

  • Pelvic osteotomy

  • Shelf operations for acetabular insufficiency

  • Inguinal lymph node dissection

  • Appendectomy

  • Total abdominal hysterectomy

• Retroperitoneal subacute mechanical - The following processes may cause a plexopathy:

  • Tumor invasion

  • Hemorrhage

  • Abscess

• Obstetric/gynecologic

  • Endometriosis - MP pain recurs and abates with menses.

  • Fetal compression during the second and third trimesters

• Subacute and chronic mechanical compression or stretching at the IL - The following situations can cause classical MP:

  • Tight-fitting garments[2]

  • Braces, trusses

  • Carpenter's belts

  • Belts for flag carriers

  • Obesity

• Other mechanical causes, including the following:

  • Reservoir for intrathecal medications placed in the right lower abdominal quadrant (personal account)

  • Ascites

  • L2, L3 root compressions

  • In multiple radiculopathies (pathology at the nerve root), muscle groups, including lumbar paraspinal muscles supplied by the L2 or L3 nerve roots, are weak or show denervation changes on electromyogram (EMG) needle examination.

• Metabolically and immunologically related causes, including the following:

  • Diabetes

  • Plexitis

• Infectious conditions - Those associated with MP include herpes zoster.

• Idiopathic causes

Indicated laboratory and radiologic studies for lateral femoral cutaneous nerve (LFCN) pathology depend on the suspected etiology and clinical impression. Meralgia paresthetica (MP) caused by obvious benign compressive forces requires no further investigation; however, the following scenarios may necessitate more testing:

• Magnetic resonance imaging (MRI) to investigate the lumbar plexus

• Serum tests for diabetes

• Radiography for possible pelvic fracture or cancer

• Computed tomography (CT) scanning for retroperitoneal hemorrhage in patients who have undergone anticoagulation therapy

A study by Suh et al indicated that ultrasonography can aid in the diagnosis of MP by determining the cross-sectional area of the LFCN. The investigators suggested that, based on the values derived from the patients in the study with unilateral MP (n=23), as well as from the controls (n=12), the cross-sectional area’s optimal cutoff value for a diagnosis of MP was 5 mm2.[15]

Electromyography is very helpful for ruling out radiculopathy, plexopathy, generalized polyneuropathy, or other neuropathic causes for the symptoms. Nerve conduction studies and somatosensory evoked potentials of LFCN have shown abnormalities in patients with MP, but these tests are unreliable and are not necessary for the diagnosis.

Caution: Discomfort over the anterolateral thigh may not be representative of LFCN injury. Referred pain can be caused by neoplastic invasion of nearby femoral or pelvic bone. In the author's experience, the pain associated with a neoplasm or bone fracture is deep, boring, and severe. MP discomfort is superficial, with fluctuating dysesthesias, paresthesias, and cutaneous hypersensitivity; it is neuropathic in quality and usually is not disabling.

See the list below:

• For classical meralgia paresthetica (MP), conservative therapy may be initiated without the necessity for invasive procedures. The diagnosis (ie, an MP secondary to trauma, irritation, or compression of the lateral femoral cutaneous nerve [LFCN] near the IL) can be verified by injecting a small quantity of lidocaine at the point of their intersection or at the point of tenderness. The discomfort should resolve transiently.

• Diagnosis of LFCN often is verified by nerve conduction studies. The LFCN is stimulated antidromically 1-2 cm medial to the ASIS above the IL; the response is recorded 12-20 cm distally over the lateral thigh. Excessively thick soft tissue makes surface stimulation technically difficult or inadequate; the examiner may choose needle stimulation instead. Right and left LFCNs are compared. Study findings are considered abnormal if there are significant side-to-side differences; there may be no response or a 50% drop in amplitude compared with the contralateral nerve. If there is no recordable response on the asymptomatic side, the results obtained when testing the symptomatic thigh are not interpretable. Asymptomatic individuals have widely variable LFCN action potentials in conduction studies.

A national cohort study by Schönberg et al indicated that in Germany, between 2005 and 2018, there was a trend toward nonsurgical management of meralgia paresthetica (MP). While, during this period, the in-hospital surgical procedure rate for MP fell from 53% to 37%, that for spinal and local injections, physical therapy, and electrotherapy rose from 23% to 30%. The investigators also saw an increase in the rate of other therapies, including those treating the psychosomatic and psychic components of MP, from 0% to 6%. Although decompressive procedures were the most frequent surgical therapies between 2005 and 2018, their rate fell from 32% to 22% over that time.[16]

Physical Therapy

Meralgia paresthetica (MP) is treated with conservative therapy, such as physical therapy, weight reduction to reduce abdominal girth, heat application, and analgesics (see Medication). Patients should avoid wearing constrictive garments, belts, or braces that impart excessive focal pressure at the IL.[2]

Physical therapy may be recommended as an adjunct to analgesic medications for pain control in patients with MP. In addition to moist heat, other modalities that may be recommended by the physical therapist include transcutaneous electrical nerve stimulation, interferential current, or low-intensity phonophoresis. These modalities are used to help alleviate pain and enable the patient to perform gentle stretching exercises with greater ease. Soft-tissue techniques (eg, trigger point therapy) also may be beneficial for pain and tightness in the hip and thigh muscles. In addition, the physical therapist may instruct the patient in a general fitness program to assist with weight reduction, as well as proper biomechanics and postural reeducation.

Patients failing conservative measures are referred to a surgeon for consideration of surgical decompression of the lateral femoral cutaneous nerve (LFCN).[3, 4, 5, 6, 7, 8] Successful predictors of excellent surgical results include positive Tinel sign, abnormal EMG, and immediate relief of symptoms following LFCN block. Although surgical transection of the LFCN has been performed for treatment, outcomes for this procedure have not been reported systematically, and some patients report worse dysesthesias.

A study by de Ruiter et al reported that histopathologic changes in the LFCN—including with regard to perineurium thickening, mucoid deposition, and percentage of collagen—occur in patients with persistent meralgia paresthetica (MP) symptoms whether or not they previously underwent neurolysis (decompression). According to the investigators, this indicates that such intraneural changes are largely irreversible in persistent MP and that treatment with neurectomy is an effective alternative to neurolysis.[17]

Injection of lidocaine to block the lateral femoral cutaneous nerve (LFCN) at the IL results in only temporary relief of symptoms. This procedure is useful for exploring which patients may respond well to surgical manipulation of the LFCN, once conservative measures have been deemed inadequate and the patient complains of chronic discomfort.

Improvement of symptoms also may occur with correction of leg length discrepancies. Use of shoe lifts or inserts may correct discrepancies sufficiently to minimize hip hyperextension on the affected side.

Trigger point injections of the sartorius muscle may help to relieve symptoms.

Steroid injections at the spinal or inguinal level may provide more chronic relief of symptoms.

In a 2011 study, an experimental therapy for meralgia paresthetica (MP) using ultrasonographically guided perineural injections (methylprednisolone acetate with mepivacaine) effectively provided significant symptom relief for patients 2 months after injection. Further studies, such as randomized placebo-controlled trials, should be performed.[18, 19]

A study by Klauser et al indicated that ultrasonographically guided steroid injection at three different levels along the LFCN can more effectively treat MP. By 12-month follow-up, 15 out of 20 patients (75%) had obtained complete symptom resolution, with the mean visual analogue scale (VAS) score having been reduced from 82 to 0, while the remaining five patients (25%) had experienced partial symptom resolution, with the mean VAS score having been reduced from 92 to 42.[20]

Medications for treatment of meralgia paresthetica (MP) discomfort include nonsteroidal anti-inflammatory drugs (NSAIDs), narcotics, and other agents, such as amitriptyline, Neurontin, and Tegretol. In general, avoid prolonged use of NSAIDs and narcotics if possible.

A TCA or anticonvulsant is started at a low dosage and titrated upward until symptoms resolve or side effects dictate otherwise. These drugs are discontinued if there is no relief with maximal quantities. A common error is stopping the medication before serum levels reach therapeutic ranges.

Suggestions for initiating chemical treatment for MP follow. The treatment of neuropathic pain varies significantly among physicians. Consult the Physicians' Desk Reference (PDR) for more detailed drug information on the following agents.

Class Summary

Use for treatment of neuropathic symptoms; the exact mechanism is unknown.

Amitriptyline (Elavil)

Good medication for neuropathic pain, often discontinued because of somnolence and dry mouth.

Class Summary

For treatment of neuropathic symptoms; the exact mechanism is unknown. These agents are used to manage severe muscle spasms and to provide sedation in neuralgia.

Carbamazepine (Tegretol)

Because of adverse side effects and risks associated with carbamazepine, this compound is initiated judiciously; prolonged use is monitored carefully.

Gabapentin (Neurontin)

Has anticonvulsant properties and antineuralgic effects; however, exact mechanism of action is unknown. Structurally related to GABA but does not interact with GABA receptors. Titration to effect can take place over several days (300 mg on day 1, 300 mg bid on day 2, and 300 mg tid on day 3). Well-tolerated and safe medication that essentially is excreted 100%.

Prognosis depends on the etiology of the lateral femoral cutaneous nerve (LFCN injury). Simple meralgia paresthetica (MP) caused by external or benign mechanical injury often remits spontaneously. In one study where the surgical candidates were selected carefully, most patients who chose nerve decompression for chronic discomfort experienced relief. Factors that indicate excellent surgical outcome are outlined in Surgical Intervention.

For most patients, this condition is self-limiting, and with education, patients learn to tolerate symptoms and modify activity, thus avoiding surgery or other aggressive treatments.

A literature review by Lu et al of patients with MP who were treated with neurectomy, neurolysis, or injection found the incidence of complete pain relief to be 85%, 63%, and 22%, respectively. The incidence of treatment complications ranged from 0-5%, being statistically comparable between the three procedures.[21]

Instruct patients to avoid activities that injure the lateral femoral cutaneous nerve.