Posterior femoral cutaneous nerve neuropathy and somatosensory evoked potentials.

Isolated posterior femoral cutaneous nerve (PFCN) entrapment has only rarely been described in the literature and never documented electrophysiologically. We report an unusual occurrence of such an injury and use somatosensory evoked potentials (SSEP) to explore the extent of the lesion. A 40-year-old woman had localized numbness of the right posterior thigh after a left putamenal hemorrhage four years before this study. She made a complete recovery from her stroke within four months; however, she continued to experience decreased sensation in the right posterior thigh. Normal sural and peroneal nerve latencies, velocities, and amplitudes were obtained in the right leg. Electromyographic examination of right leg and related para spinal musculature was unremarkable. SSEP were then performed with CZ'-FZ (10-20 system) electrode placement. Normal sural, lateral femoral cutaneous, and posterior tibial responses were obtained bilaterally. Response differences consistent with an isolated right PFCN neuropathy were observed. The perfectly symmetric SSEP responses for the sural, lateral femoral cutaneous, and posterior tibial nerves obviate a central, and substantiate a peripheral, cause for the altered right PFCN evoked response.