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“Normal” electromyographic silent periods (SPs), produced by electrical stimulation of digital nerves, were recorded in the voluntarily contracting abductor pollicis brevis (APB) muscle of a patient with pure sensory neuronopathy and absent sensory nerve action potentials (SNAPs). Such findings implicate the smaller, slower conducting fibers in the genesis of the cutaneous silent period. These same fibers may be activated during more proximal stimulation to contribute to the latter portions of the mixed nerve silent period. 0 1992 John Wiley & Sons, Inc. Key words: silent period electromyography inhibition peripheral nerve sensory neuropathy MUSCLE 81 NERVE 15:1345-1348 1992

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THE SILENT PERIOD IN PURE SENSORY NEURONOPATHY A. ARTURO LEIS, MD, MARKUS KOFLER, MD, and MARK A. ROSS. MD

T h e physiologic mechanisms that contribute to produce the electromyographic silent period (SP) following electrical stimulation of mixed or cutaneous nerves remain uncertain. 1*2,4-8 We present a patient with pure sensory neuronopathy and absent sensory nerve action potentials (SNAPs) in which cutaneous and mixed nerve SPs were easily elicited. Such cases may help to elucidate the types of nerve fibers involved in the genesis of the SP. CASEREPORT

A 74-year-old woman was evaluated for predominantly distal numbness and painful dysesthesias involving all limbs. Symptoms began approximately 30 years prior to the current evaluation and included burning and numbness in the fingers and hands which had worsened over the past few years. She reported that touching fabrics or paper felt “like ripping the hands to pieces” which prompted her to stop sewing and writing. She also noted loss of balance and difficulty walking. Neu-

From the Division of Restorative Neurology and Human Neurobiology, Baylor College of Medicine, Houston, Texas (Drs. Leis and Kofler); and Department of Neurology, University of Iowa Hospitals and Clinics, Iowa City, Iowa (Dr. Ross) Acknowledgments: The authors thank Tina Martinez-Barrett for preparation of the manuscript. Research was funded by the Vivian L. Smith Foundation for Restorative Neurology, Houston, Texas. Address reprint requests to A. Arturo Leis, MD, Division of Restorative Neurology and Human Neurobiology. Baylor College of Medicine, Smith Tower, Suite 1901, 6550 Fannin, Houston, TX 77030. Accepted for publication May 2, 1992. CCC 0148-639X/92/121345-04 0 1992 John Wiley & Sons, Inc

Silent Period

rological examination revealed a profound loss of vibration and position sense in digits and toes bilaterally. Stretch reflexes were absent and muscle tone was normal to hypotonic. Slight dysmetria was noted on finger-nose test bilaterally, and gait was slow and unsteady with a wide-based stance. A positive Romberg sign was present, and the patient was unable to stand on either leg. Nerve conduction studies (Table 1) showed absence of all SNAPs in the upper extremities with normal motor nerve conduction studies. Cervical somatosensory evoked potentials (CSEP) following stimulation to either median nerve at the wrist failed to evoke reproducible Erb’s potentials or cervical N11 and N13 responses. T h e cortical N20 potential was absent following left median nerve stimulation and poorly defined and of low amplitude (

The silent period in pure sensory neuronopathy.

"Normal" electromyographic silent periods (SPs), produced by electrical stimulation of digital nerves, were recorded in the voluntarily contracting ab...
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