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 <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 818 patients, respectively. The VERs were abnormal in 7/10 patients. Wefound 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.