Re:Re: meralgia paresthetica

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pure sensory nerve

The lateral femoral cutaneous nerve, a pure sensory nerve, is susceptible to compression as it courses from the lumbosacral plexus, through the abdominal cavity, under the inguinal ligament, and into the subcutaneous tissue of the thigh. 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 nerve.

Lateral Femoral Cutaneous Nerve Syndrome Secondary to Ascites

Marcello Cherchi, MD, PhD
Resident
Department of Neurology

Warren H. Wallace, MD
Associate Professor
Department of Internal Medicine

Northwestern University Feinberg
School of Medicine
Chicago, Ill

The lateral femoral cutaneous nerve syndrome is a mononeuropathy characterized by dysesthesia or anesthesia in the anterolateral thigh. Symptoms range from mild and transitory to severe and disabling. The syndrome is underdiagnosed in part because of the difficulty many patients have in describing their symptoms. A litany of factors have been implicated as triggers.

The lateral femoral cutaneous nerve syndrome was first described in 1895 by Martin Bernhardt¹ and Vladimir K. Roth.² In addition to its eponymous designation as the Bernhardt-Roth syndrome, it was known as meralgia paresthetica (from the Greek “meros” for thigh and “algos” for pain)³ and eventually received an anatomically based appellation. This benign, but often distressing, entrapment neuropathy is reportedly second in preval‎ence only to sciatica among peripheral nerve disorders of the lower extremity⁴ and was said to have affected Sigmund Freud.

One study encompassing 173,375 patient-years demonstrated that the incidence is approximately 4.3 per 10,000 person-years, thus primary care physicians are likely to encounter the condition at least once every year.⁵

The lateral femoral cutaneous nerve arises from the second and third roots of the lumbar plexus. It penetrates the psoas muscle, crosses the ilia­­cus muscle by passing through an opening medial to the anterior superior iliac spine under the inguinal ligament (specifically, between the attachments of the lateral part of the inguinal ligament to the anterior superior iliac spine), where it is in opposition to the bone and the sartorius muscle. After this mostly horizontal abdominopelvic course, the nerve turns at a sharp angle and courses inferiorly, before continuing into the subcutaneous tissue of the thigh immediately below the fascia lata (Figure). In its caudal course, it divides into 2 branches, with the anterior division supplying the skin of the anterior thigh to the knee, and the posterior division supplying the skin of the upper half of the lateral thigh. Thus, the nerve supplies the anterolateral aspect of the thigh, from the level of the inguinal ligament almost to the knee. Compression (entrapment) of the nerve often occurs at the point where it passes between the inguinal ligament and the sartorius muscle.

Symptoms
The symptoms of lateral femoral cutaneous nerve syndrome include unpleasant sensations in the distribution of the nerve, variously described as pain, numbness, tingling, burning, itching, sensitivity, or some combination thereof. Symptoms can range from mild to severe and are sometimes worse after walking or standing. Sitting can either relieve or worsen the pain, depending on the patient.³

Physical examination may reveal decreased pinprick and touch sensation, dysesthesias, hyperesthesias, or allodynia in the distribution of the nerve. Alopecia over the affected area has been reported.^4,6 Pressure at the inguinal ligament medial to the anterior superior iliac spine may elicit pain, allodynia, and dysesthesias. Since this nerve is exclusively sensory, motor deficits (eg, quadriceps weakness) or changes in deep-tendon reflexes (eg, the patellar reflex) are not involved in this syndrome. About 80% of cases are unilateral.⁷ Bilateral cases have been reported in association with pelvic inflammatory disease⁸ and multiple abdominal surgeries.⁹

Common Causes
Lateral femoral cutaneous nerve syndrome has been attributed to or associated with a variety of phenomena (Table). The syndrome can occur secondary to direct extrinsic compression, such as by clothing, belts, tight waistbands, pantyhose, wallets, or pocket watches. Positional factors, such as leg-length discrepancy or pelvic tilt, can contribute. Symptoms may appear immediately after seatbelt-related injury³ or medical procedures in which instrumentation was used (eg, cardiac catheterization¹⁰). The syndrome may also be a complication of many surgeries, including inguinal herniorrhaphy, groin flap, inguinal lymphadenectomy, iliac bone harvesting, laparoscopic cholecystectomy, gastroplasty, arthroplasty, cesarean section, and coronary artery bypass graft surgery.

It can occur in the context of systemic diseases, such as hypothyroidism or diabetes, and it may be the initial manifestation of an underlying illness, such as malignancy, chronic appendicitis, abdominal aortic aneurysm, hemangiomatosis, or pelvic avulsion fracture. Familial cases have been reported.¹¹ Pathologic processes that can mimic the syndrome include neurologic lesions that are more proximal (eg, lumbar disk herniation,¹² spinal stenosis,¹³ lumbar radiculopathy¹⁴) and urinary retention.¹⁵ The differential diagnosis also includes osteoarthritis.¹⁶

This syndrome has been associated with obesity and pregnancy, which involve abdominal distension as a common mechanism. Merely having a “large abdomen” seems to be enough of a trigger,¹⁷ presumably because the tissues impinge or exert traction on the nerve. We describe a case that suggests ascites as a cause of the syndrome, an association reported in much older articles; a PubMed search revealed only 1 relevant recent article.¹⁸

Illustrative Case
A 62-year-old man presented to a Veterans Administration hospital complaining of abdominal discomfort and left thigh pain. He noticed increasing abdominal distension in the past 6 months and increasing left thigh pain and burning in the preceding 3 weeks. His history included hypertension, anxiety, depression, chronic low back pain, cirrhosis from hepatitis C virus infection (acquired from a blood transfusion), and a 30-year history of alcoholism. His medications included a nonsteroidal antiinflammatory drug (NSAID), a beta-blocker, furosemide, folate, thiamine, and lorazepam.

Notable physical findings included mild tenderness on firm palpation of the lumbar spine; the abdomen was markedly distended and taut, with 25 cm of shifting dullness, a subumbilical midline scar (from a childhood appendectomy), and a small supraumbilical ventral hernia; pitting edema of the lower abdominal wall and mild tenderness to deep palpation in the lower quadrants were also evident.

The patient had exquisite tenderness to light touch of the left anterolateral thigh; when seated, he would experience intermittent lancinating pain in this area. There were no visible skin abnormalities. Neurologic examination was unremarkable. Initial laboratory studies were significant only for mildly elevated total and direct bilirubin. Findings of Doppler ultrasound of the liver were consistent with cirrhosis, splenomegaly, and ascites, with no masses or thrombi.

Analysis of ascitic fluid obtained during diagnostic and therapeutic paracentesis revealed a serum–ascites albumin gradient reflecting portal hypertension, with no evidence of infection or malignancy. Although the appearance of the abdomen was only minimally changed after paracentesis, the patient reported substantial relief of pain and discomfort . After 2 days, however, the pain in the left thigh gradually increased and spread to the right thigh. The patient was discharged with a prescription for fu­rosemide and spironolactone.

Diagnosis
Lateral femoral cutaneous nerve syndrome is largely a clinical diagnosis. Although electromyography has been used,¹³ it generally plays little role in the eval‎uation.³ A consistently reliable diagnosis can be made by first ruling out more proximal (ie, L1, L2, L3) nerve-root involvement based on the physical examination and imaging studies. The physician should then map the area of dysesthesia to determine if it is in the distribution of the lateral femoral cutaneous nerve and inject a small amount of anesthetic into the area where the nerve passes the anterior superior iliac spine.³ Patients with the syndrome should experience immediate pain relief.

In our patient, the distribution and character of the burning anterolateral thigh pain and tenderness to light touch strongly suggested the syndrome. Other conceivable etiologies include a more proximal neurologic lesion (eg, lumbar radiculopathy, given the man’s history of chronic low back pain and midline tenderness on physical examination) or a distant sequela of his childhood appendectomy. However, the accelerated abdominal distension coinciding with the onset of the anterolateral thigh dysesthesias implicated the ascites as the culprit.

Ascites itself, of course, has an extensive differential diagnosis, including portal hypertension (resulting from cirrhosis, alcoholic hepatitis, hepatic congestion, portal-vein occlusion, or hypervitaminosis A), hypoalbuminemia (eg, nephritic syndrome, protein-losing enteropathy, lymphangiectasia, severe malnutrition), hypothyroidism, ovarian disorders (ie, Meigs’ syndrome, struma ovarii, malignancy), other gynecologic conditions (eg, endometriosis, ruptured dermoid cyst), pancreatic disorders (eg, rupture of pseudocyst, pancreatic duct leak), peritoneal metastatic disease, bilious ascites (gallbladder rupture or traumatic leak), chylous ascites, infections, familial Mediterranean fever, peritoneal vasculitides (eg, systemic lupus erythematosus, Henoch-Schönlein purpura), granulomatous peritonitis, Whipple’s disease, sarcoidosis, amyloidosis, and Wilson’s disease.

Treatment
Treatment usually begins with conservative measures, such as analgesics and NSAIDs, advice on wearing loose clothing and weight loss, and the prudent use of local anesthetics and steroids.³ Nonresponsive patients may benefit from surgery, although the best operative approach is a subject of debate. In a series of 14 adult patients seen over a period of 4 years, conservative treatment provided long-lasting benefit in 5 patients, whereas surgical decompression or resection resulted in a good outcome in all but 1 of the 8 patients who opted for surgery.³

Conclusion
Lateral femoral cutaneous nerve syndrome is a relatively common condition that can be easily missed or misdiagnosed by the unsuspecting physician. Although ascites is not often a cause, it should be considered in the differential diagnosis when a patient presents with abdominal distension associated with anterolateral thigh pain, allodynia, or dysesthesia.

Self-assessment test
1. Which of these statements about lateral femoral cutaneous nerve syndrome is NOT true?
A. Familial cases have been reported
B. It can be the initial sign of a psoas muscle tumor
C. It may be associated with diabetes
D. Electromyography is usually used for diagnostic confirmation

2. All these symptoms are common features of the syndrome, except:
A. Burning pain
B. Tingling pain
C. Numbness
D. Quadriceps muscle weakness

3. Which factor is most often associated with bilateral involvement?
A. Tight belt
B. Seatbelt trauma
C. Pelvic inflammatory disease
D. Obesity

4. All these conditions are included in the differential diagnosis, except:
A. Urinary retention
B. Benign prostatic hyperplasia
C. Spinal stenosis
D. Osteoarthritis

5. Which of the following options is generally not recommended as initial treatment?
A. Local anesthetics
B. Loose-fitting clothing
C. Exercise
D. NSAIDs

(Answers at end of reference list)

References
1. Bernhardt M. Ueber isoliert im gebiete des nervus cutaneous femoris externus vorkomnende paresthesien. Neurol Zbl. 1895;14: 242-244.

2. Roth VK. Meralgia päeresthetica. Med Obozr Mosk. 1895; 43:678-688.

3. Ivins GK. Meralgia paresthetica, the elusive diagnosis: clinical experience with 14 adult patients. Ann Surg. 2000; 232:281-286.

4. Aranoff SM, Levy HB, Tuchman AJ, et al. Alopecia in meralgia paresthetica. J Am Acad Dermatol. 1985; 12: 176-178.

5. van Slobbe AM, Bohnen AM, Bernsen RM, et al. Incidence rates and determinants in meralgia paresthetica in general practice. J Neurol. 2004; 251:294-297.

6. Nabavi DG, Georgiadis D, Stogbauer F, et al. Meralgia paresthetica. A rare differential diagnosis of circumscribed alopecia [in German]. Dtsch Med Wochenschr. 1996; 121:834-838.

7. Victor M, Ropper AH. Diseases of the peripheral nerves. In: Wronsiewicz MJ, Medina MP, Navrozov M, eds. Adams and Victor’s Principles of Neurology. 7th ed. New York, NY: McGraw-Hill; 2001:1370-1445.

8. Rotenberg AS. Bilateral meralgia paresthetica associated with pelvic inflammatory disease. CMAJ. 1990;142:42-43.

9. Rajabally YA, Farrell D. Bilateral meralgia paraesthetica following repeated laparotomies. Eur J Neurol. 2003;10:330-331.

10. Butler R, Webster MW. Meralgia paresthetica: an unusual complication of cardiac catheterization via the femoral artery. Catheter Cardiovasc Interv. 2002;56:69-71.

11. Massey EW. Familial occurrence of meralgia paraesthetica. Arch Neurol. 1978;35:182.

12. Trummer M, Flaschka G, Unger F, et al. Lumbar disc herniation mimicking meralgia paresthetica: case report. Surg Neurol. 2000;54:80-81.

13. Cubukcu S, Karsli B, Alimoglu MK. Meralgia paresthetica and low back pain. J Back Musculoskel Rehabil. 2004;17: 135-139.

14. Kallgren MA, Tingle LJ. Meralgia paresthetica mimicking lumbar radiculopathy. Anesth Analg. 1993;76:1367-1368.

15. Pollen JJ. Chronic urinary retention masquerading as meralgia paraesthetica. Br J Urol. 1991;68:554-555.

16. Seror P, Seror R. Meralgia paresthetica: clinical and electrophysiological diagnosis in 120 cases. Muscle Nerve. 2006;33:650-654.

17. Deal CL, Canoso JJ. Meralgia paresthetica and large abdomens. Ann Intern Med. 1982;96:787-788.

18. Pauwels A, Amarenco P, Chazouilleres O, et al. Unusual and unknown complication of ascites: meralgia paresthetica [in French]. Gastroenterol Clin Biol. 1990;14:295.