Motor evoked potentials (MEP) from the external urethral sphincter (EUS) to assess neurogenic incontinence in patients with spinal cord injuries

Purpose: A prospective study is presented that assessed neurogenic lesions of the somatic motor efferent potentials (MEP) and simultaneously recorded urodynamics (UD). Materials and Methods: 9 healthy subjects and 33 patients 15 x spinal cord injury, 14 x cauda equina lesions and 4 x multiple sclerosis (MS) - with ne urogenic urinary incontinence were examined by means of urodynamics and ele ctrophysiology. MEP responses from the EUS were evoked after transcranial ( tc) and lumbosacral (Is) single, pulse magnetic stimulation. A ratio out of tc/ls latencies was calculated to distinguish between central and peripher al lesions. The mechanical EUS pressure responses were recorded simultaneou sly with the EMG recordings using a microtipp pressure transducer catheter with an integrated bipolar surface electrode. Results: in 9 healthy subjects the spinal latency was 19.0 ms, the peripher al latency was 4.25 ms and the ratio was 4.4. In patients with spinal cord lesion, spinal latency was significantly delayed (22.7 ms), whereas periphe ral latency was normal. The ratio increased to 5.5. Of these 15 patients, 1 3 suffered from neurogenic incontinence. Patients with a complete spinal le sion showed no EUS responses after tc stimulation, whereas peripheral answe rs were normally elicitable. Patients with MS showed significantly longer s pinal latencies (25.5 ms). The increased ratio of 6.0 indicated a spinal le sion. Of the patients with severe cauda equina lesions and urinary incontin ence, 10 had normal spinal latencies, but longer peripheral latencies of 6. 7 ms. The ratio of 3.4 indicated a lesion of the sacral caudal roots. In pa tients with complete cauda injury neither spinal nor peripheral responses c ould be evoked. Tc-evoked mechanical pressure responses from the EUS could only be recorded in intact or incompletely injured spinal and peripheral mo tor nervous pathways, whereas they could be evoked after Is stimulation onl y in cases with partially preserved sacral caudal roots independent of a sp inal lesion. Conclusions: MEP and evoked pressure responses from the EUS proved to be an additional. and well-tolerable diagnostic tool in the assessment of neurog enic incontinence. Spinal and peripheral lesions of the motor efferent path ways to the EUS can thereby be distinguished.