A test for the evaluation of the lateral cutaneous branch of the iliohypogastric nerve using somatosensory evoked potentials

Iliohypogastric nerve (IHN) lesions are rare and usually due to abdominal surgery or trauma. There is no established electrophysiologic test for evaluating this nerve. A method is proposed to evaluate the IHN lateral cutaneous branch using somatosensory evoked potentials (SSEP). SSEP were elicited in 20 subjects using electrical stimulation from the greater trochanter up to 7 cm posterior to a point on the posterior axillary line, at the level of the greater trochanter. The active recording electrodes were placed 2 cm behind the Cz electrode in the midline, and the reference electrode midway between the Fpz and Fz electrodes in the midline. Stable responses were elicited in 19 / 20 subjects (12 male), aged 19-52 years (mean 32 ± 6.6). Average positive peak onset latency was 32.5 ± 3.7 msec, average amplitude 0.96 ± 0.4 μV. Side-to-side latency difference range was 0-3.7 msec and amplitude difference range 0.06-1.04 μV. The technique proved sensitive in two cases with IHN injury following trauma, a 24-year-old male with a large hematoma over the right hip from the iliac crest to the greater trochanter tested twice one year apart, with stable repeat responses, and a 26-year-old female who sustained a crush injury to the right lateral pelvis. A side-to-side latency difference > 3.7 msec or a unilateral absent response should be regarded as abnormal. This test may be useful for confirming the clinical picture of IHN lateral cutaneous branch lesions.