This week we’re going to review meralgia paresthetica (MP), a neuropathy of the Lateral Femoral Cutaneous Nerve (LFCN). The LFCN is responsible for cutaneous innervation of the anterolateral thigh and variable arises from the L1-L3 nerve roots. Overall, there is a paucity of research on MP which makes diagnosis and treatment challenging. MP most commonly occurs among middle age males and is bilateral up to 20% of the time. The incidence is approximately 32-43 cases per 100,000 individuals which increases to 247 cases per 100,000 individuals among diabetics.
MP is characterized by compression of the LFCN resulting in pain, paresthesias, and sensory loss in the same distribution. Etiology can roughly be broken down into two categories: idiopathic (or spontaneous) or iatrogenic due to surgical procedures.
Idiopathic cases can be challenging to diagnose as there is often no clear cause in the history of physical exam. Generally, risk factors must be reviewed to help suggest the cause. Among athletes, cases have been documented in gymnastics, basketball, soccer, bodybuilding and strenuous exercise. Other commonly acknowledged risk factors include obesity, diabetes, advanced age, hypothyroidism, scoliosis and alcoholism. Occupations such as police and military are often noted where the occupation requires “tight garments” or a belt. Seat belts, muscle spasm and direct trauma have also been implicated.
Iatrogenic cases are slightly different in that the absence of MP pre-operatively allows the physician to point to the surgery as the most clear cause. In general, MP is associated with total hip arthroplasty (THA), anterior hip resurfacing and lumbar spine surgery. In one study, 81% of patients developed MP following THA (Goulding 2010). Among spine surgeries, studies have shown 12-20% of patients go on to develop MP (Gupta 2004, Mirovsky 2000). Less commonly implicated procedures include iliac bone harvesting, open and laparoscopic appendectomy, cesarean section with epidural analgesics, and OBGYN surgery, Among children, a history of osteoid osteoma surgery is considered a risk factor (Goldberg 1975)
Diagnostic modalities are limited. EMG/NCS have sensitivity in the 65-81% range (Seror 2004). MR Neurography should be considered and discussed with your radiology service. Chhbara et al found overall diagnostic accuracy to be 90-91% (Chhabra 2013). US guided nerve block around the inguinal ligament may be the most diagnostically valuable tool. Alternatively, a palpation guided injection 1cm medial and inferior to the ASIS or at the point of maximum pain can be utilized.
Most patients do well with 85% of individuals recovering with conservative treatment (Dureja 1995). There are no evidence based guidelines for management, although physicians typically start with a conservative approach. The primary goal should be to treat the offending activity, i.e. if wearing a belt too tightly, change belts or uniform. Analgesics should be considered including neuropathic pain medications. Physical therapy and manual therapy can be used. The primary procedure is probably ultrasound guided corticosteroid injections which have shown excellent results (Tagliafi 2011, Tumber 2008). Additional treatments with weak evidence include kinesiology tape, acupuncture with cupping, pulsed radiofrequency ablation and one case report of a spinal cord stimular. The indications for surgery are not well established but most techniques involve either LFCN neurolysis or resection, with the later appearing to be more curative (de Ruiter 2012).