Objective: To investigate the source of an unusual and previously unreported v olume conducted potential on motor nerve conduction studies. In a case of subacu te ulnar neuropathy at wrist (UNW) selectively involving ...Objective: To investigate the source of an unusual and previously unreported v olume conducted potential on motor nerve conduction studies. In a case of subacu te ulnar neuropathy at wrist (UNW) selectively involving the deep motor branch, we recorded from the hypothenar eminence a large positive wave(2.5 ms-2 mV) pre ceding the negative takeoff of the delayed distal ulnar motor response. Methods: We performed multiple channels motor and sensory ulnar nerve (UN) conduction st udies; these included selective electrical stimulation and anaesthetic block of UN branches and also selective recording of motor responses by single fibre need les; data were confirmedby an intraoperative neurophysiological study and correl ated with MRI and surgical findings. Results: Detailed neurophysiological invest igation demonstrated the generation of this waveform from the palmaris brevis (P B) muscle. MRI and surgical exploration documented a hypertrophy of this muscle. Conclusions: In type II°UNW, depolarization of a spared palmaris brevis muscle may be recorded as a positive wave preceding the delayed abductor digiti minimi motor response.Significance: We underline the peculiar localizing value of this volume conducted ’meaningful artefact’in that particular setting. It actually represented an early neurographic analogue of what is known as the clinical ‘P almaris Brevis Sign’in long standing type II°UNW.展开更多
文摘Objective: To investigate the source of an unusual and previously unreported v olume conducted potential on motor nerve conduction studies. In a case of subacu te ulnar neuropathy at wrist (UNW) selectively involving the deep motor branch, we recorded from the hypothenar eminence a large positive wave(2.5 ms-2 mV) pre ceding the negative takeoff of the delayed distal ulnar motor response. Methods: We performed multiple channels motor and sensory ulnar nerve (UN) conduction st udies; these included selective electrical stimulation and anaesthetic block of UN branches and also selective recording of motor responses by single fibre need les; data were confirmedby an intraoperative neurophysiological study and correl ated with MRI and surgical findings. Results: Detailed neurophysiological invest igation demonstrated the generation of this waveform from the palmaris brevis (P B) muscle. MRI and surgical exploration documented a hypertrophy of this muscle. Conclusions: In type II°UNW, depolarization of a spared palmaris brevis muscle may be recorded as a positive wave preceding the delayed abductor digiti minimi motor response.Significance: We underline the peculiar localizing value of this volume conducted ’meaningful artefact’in that particular setting. It actually represented an early neurographic analogue of what is known as the clinical ‘P almaris Brevis Sign’in long standing type II°UNW.
