Final Diagnosis

Patient Follow-up

The patient underwent diet control and regular exercise. He also took Gabapentin for pain control. He intentionally lost 40 pounds over 1 year with improvement of his sensory symptoms.

Discussion

Meralgia paresthetica is a focal neuropathy which is caused by compression of the LFCN at the level of the anterior-superior iliac spine or inguinal ligament . The disease can be associated with obesity, diabetes mellitus, wearing tight low cut trousers, and strenuous walking and cycling, among others [1–4]. Patients with meralgia paresthetica commonly present with pain, burning, tingling, and/or numbness in the lateral or anterolateral thigh [5], which can mimic upper lumbar radiculopathy [6, 7]. A reliable and sensitive diagnostic test is needed not only to confirm the diagnosis but also to distinguish it from lumbar radiculopathy. LFCN NCS is often technically challenging due to the high anatomical variability of the nerve and the obesity of patients [1, 4, 8, 9] as seen in our case. Although the symptoms were unilateral in our patient, NCS showed absent LFCN conduction responses bilaterally; therefore, it was non-diagnostic. Using ultrasound-guide surface electrode placement may greatly improve the sensitivity of the test, but it is still suboptimal in evaluating markedly obese patients as the response is difficult to obtain and the interside variability is high [10]. Imaging studies , including ultrasound and magnetic resounance neurography (MRN), may be useful [11–14], but further confirmatory studies are needed and MRN is not widely available.

LFCN arises from the L2 and L3 nerve roots. The nerve specimens derived from neurectomy of patients with chronic meralgia paresthetica showed selective loss of large myelinated fibers with varying degree of intraneural and epineural inflammation [15]. A functional study also suggested small fiber involvement as warm and heat pain sensation thresholds were increased and contact heat-evoked potentials (CHEPs) were reduced in the affected side of 14 patients with meralgia paresthetica as compared with unaffected side and 14 normal controls [16]. Along with the prominent small sensory fiber symptoms and signs in the affected areas of meralgia paresthetica, we studied the diagnostic utility of skin biopsy in this condition, and we found that meralgia paresthetica was indeed associated with focal loss of intraepidermal nerve fibers at the lateral proximal thigh [17]. Therefore, skin biopsy with IENFD evaluation is useful in the diagnosis of this disease. Similar to NCS, skin biopsy can differentiate sensory neuropathy from sensory radiculopathy, as IENFD can be affected by sensory neuropathy but should not be affected by preganglionic root lesions.

Meralgia paresthetica affects anterolateral proximal thigh, and the normal IENFD has been established at the proximal thigh by most cutaneous nerve laboratories. When evaluating meralgia paresthetica, we biopsy bilateral proximal thighs to make a side-to-side comparison and to correlate the IENFD reduction with the side of symptoms and signs. We also biopsy the distal leg to rule out a more generalized peripheral neuropathy as the cause of reduced IENFD at the affected thigh. Our patient did have a distal small fiber neuropathy, which was most likely due to the prediabetes. But the absent IENF at the affected proximal thigh is out of proportion to the borderline reduced IENFD at the distal leg. The absent IENF at the proximal thigh is felt to be due to the meralgia paresthetica rather than related to the distal SFN, and it is unlikely to represent a non-length-dependent SFN given his clinical presentation. The meralgia paresthetica in our patient is mainly caused by the obesity. Prediabetes may also contribute. The key management is weight reduction by lifestyle modification. Pain control is also important. The symptoms of our patient, both pain and numbness, have improved after 1 year of lifestyle modification with reduction of 40 pounds of body weight.

Skin biopsy has been shown useful for assessing focal neuropathies with small fiber degeneration , which include complex regional pain syndrome and diabetic truncal neuropathy in addition to meralgia paresethetica [17–19]. If no normative values are established at the affected sites, the contralateral unaffected sites should also be biopsied for comparison.

Pearls