103 - Neuromuscular Ultrasound of Meralgia Paresthetica: A Focal Entrapment of the Lateral Femoral Cutaneous Nerve Adjacent to the Anterior Superior Iliac Spine

A 32-year-old male presented with left leg paresthesia. Examination revealed diminished light touch sensation on the left anterolateral thigh and normal leg strength. Nerve conduction studies (NCS) showed an absent left lateral femoral cutaneous nerve (LFCN) sensory response with preservation on the right. Left lower limb needle electromyography (EMG) was normal. NMUS revealed focal left LFCN enlargement (cross-sectional area [CSA] 6.2 mm²) localized to the ASIS compared to the right (CSA 1.6 mm²). These sonographic and electrodiagnostic (EDX) findings confirmed a left LFCN mononeuropathy. Conservative management ensued with gabapentin, activity modification, and loose-fitting clothing.

Discussions:

Meralgia paresthetica is a focal mononeuropathy caused by compression of the LFCN as it passes beneath or through the inguinal ligament at the ASIS. NCS may reveal absent or diminished responses; however, the diagnostic yield is often limited by anatomical variability and technical challenges, such as body habitus. Given the pure sensory component of the LFCN, the EMG is normal. NMUS can be instrumental in directly visualizing focal LFCN enlargement, a finding that correlates with focal nerve compression. Sonographically determined nerve CSA asymmetry with side-to-side comparison provides a robust anatomical correlation to the patient’s clinical symptoms. These findings underscore the utility of NMUS in the assessment of entrapment mononeuropathies, particularly when EDX results are equivocal or when anatomical confirmation is required.

Conclusions:

There is diagnostic utility in NMUS for meralgia paresthetica. Sonographic identification of LFCN entrapment may complement EDX testing and guide conservative management.