Meralgia Paraesthetica

Meralgia paraesthetica is a mononeuropathy of the lateral femoral cutaneous nerve (L2 and L3), usually from entrapment as the nerve passes under or through the inguinal ligament near the anterior superior iliac spine, producing burning, tingling or numbness on the anterolateral thigh without weakness.

• The nerve is purely sensory, so there is no motor weakness and no change in the knee jerk.
• Incidence about 4 per 10 000 person years; commoner in men and in middle age.
• Risk factors: obesity, pregnancy (especially third trimester), diabetes, tight belts, corsets, body armour or trousers, prolonged standing or walking, sudden weight loss, leg length discrepancy, hip or pelvic surgery, seat belt injury, and abdominal or pelvic mass.
• Most cases resolve with removal of the cause.

• Burning pain, numbness, tingling, hypersensitivity (clothes touching the skin) and sometimes a "wet" or "cold" sensation over the anterolateral thigh, from the inguinal region to just above the knee; usually unilateral (bilateral in about 20 percent).
• Worse on standing, walking, hip extension or lying on the affected side; relieved by sitting or hip flexion.
• Examination: reduced sensation to pinprick and light touch in the oval patch over the lateral thigh; tenderness 1 to 2 cm medial and inferior to the anterior superior iliac spine; Tinel sign over the nerve; pelvic compression test (sitting with the pelvis compressed for 45 seconds relieves symptoms); symptom provocation by hip extension.
• No weakness of the quadriceps and no change of the patellar reflex; back examination is normal.

• Clinical diagnosis; a diagnostic nerve block with 5 to 10 mL of lidocaine 1 percent medial to the anterior superior iliac spine that abolishes the symptoms is confirmatory.
• Exclude: glucose or HbA1c (diabetes), thyroid function, and vitamin B12.
• Ultrasound or MRI of the pelvis and abdomen for symptoms that are atypical, bilateral, progressive, or when an abdominal, pelvic or retroperitoneal mass is suspected.
• Nerve conduction studies are technically difficult but may exclude lumbar radiculopathy and femoral neuropathy; MRI lumbar spine when radiculopathy is suspected.
• Differentials: L2 or L3 radiculopathy (weakness, back pain, reflex change), femoral neuropathy (quadriceps weakness, absent knee jerk), lumbar plexopathy, hip osteoarthritis, trochanteric bursitis, diabetic neuropathy, spinal cord disorder, tumour, and iliopsoas haematoma.

Remove precipitants

• Avoid tight clothing, belts and heavy tool belts; wear loose clothing; avoid prolonged hip extension and standing.
• Weight reduction in obesity; optimise glycaemic control in diabetes.
• Reassure: most settle within weeks to months (about 85 percent improve with conservative treatment).

Symptomatic treatment

• Topical: lidocaine 5 percent medicated plaster applied for up to 12 hours in 24; capsaicin 0.075 percent cream three to four times daily; capsaicin 8 percent patch applied for 30 minutes (specialist).
• Neuropathic agents: amitriptyline 10 mg orally at night increasing to 50 mg; gabapentin 300 mg at night increasing to 300 to 600 mg three times daily (maximum 3600 mg daily); pregabalin 75 mg twice daily increasing to 150 mg twice daily; duloxetine 30 mg daily increasing to 60 mg. Adjust gabapentinoids by creatinine clearance.
• NSAIDs for a short course: ibuprofen 400 mg three times daily with food for up to 2 weeks.

Injection

• Local infiltration near the anterior superior iliac spine with lidocaine 1 percent 5 mL and methylprednisolone 40 mg (or triamcinolone 20 to 40 mg) under ultrasound where possible; relief in about 60 to 90 percent; repeat up to 3 times at intervals of at least 4 weeks.

Refractory cases

• Pulsed radiofrequency; surgical neurolysis (decompression) or neurectomy (leaves permanent numbness) for symptoms that persist for over 6 to 12 months and impair function.

Special groups

• Pregnancy: reassure; symptoms usually resolve after delivery; avoid tight clothing and use hip flexion rest; local lidocaine and paracetamol only; avoid NSAIDs and gabapentinoids unless essential.