Repetitive discharge on high-frequency stimulations in a case of neuropathy

Abstract

We studied abnormal late potentials elicited by high-frequency stimulations in a case of neuropathy. The patient was a male aged 16 years and 5 months, who presented with muscular weakness and atrophy in the right hand. He showed no sensory abnormalities except for slight hypopallesthesia. Initial examination revealed reduced compound muscle action potential (CMAP) in the right ulnar nerve, reduced F-wave appearance ratio in both the median and right ulnar nerves, induction of abnormal late potentials in the right median and ulnar nerves with high-frequency stimulations, and induction of abnormal late potentials in the right ulnar nerve immediately after an exercise test. Needle electromyography revealed long-duration polyphasic potentials and high-amplitude motor unit action potentials in the right abductor pollicis brevis. In terms of amplitude, we classified the abnormal late potentials into repetitive discharges, small repetitive discharges and fasciculation-like waves. The appearance and amplitude of repetitive discharges decreased after intravenous immunoglobulin (IVIg) therapy. As his grip strength improved with treatment, the repetitive discharges in the right median nerve and the small repetitive discharges in the right ulnar nerve decreased. In this patient, axonal neuropathy was suspected on the basis of the decrease in the amplitude of CMAP and the reduced F-wave appearance ratio in the right ulnar nerve. In the patient, the change of late potentials correlated well with the improvement of the clinical symptoms.