The neurophysiological profile of vitamin B12 deficiency

Reports of the incidence and severity of physiological abnormalities of vitamin B12 deficiency sharply differ. To resolve these controversies we performed evoked response and nerve conduction studies in 10 males with vitamin B12 deficiency. The minimum criteria for this diagnosis were diminished position and vibration sensation and vitamin B12 levels less than 220 pg/ml. We found normal BAERs in 9/10 patients. The central interpeak latencies of the median and peroneal SERs were abnormal in 4/10 and 8/8 patients, respectively. The VERs were abnormal in 7/10 patients. We found absent or diminished amplitudes of sural sensory and peroneal motor action potentials in 8/10 patients. Abnormal peroneal F response chronodispersion was present in 7/10 patients. Nerve conduction velocities (NCV) were normal in 9/10 patients. EMG demonstrated abnormalities consistent with denervation in lower extremity muscles in 8/10 patients. These studies present a profile of vitamin B12 deficiency: essentially normal BAERs, mildly abnormal VERs and median SERs, and markedly abnormal peroneal SERs. NCV studies are consistent with sensory-motor axonopathy.