Dorsal sural nerve conduction study in vitamin B(12) deficiency with megaloblastic anemia

Peripheral neuropathy is frequently observed in B(12) deficiency. In spite of this, there is little knowledge about peripheral neuropathy in B(12) deficiency because the severity of clinical involvement of the central nervous system clearly outweighs signs and symptoms due to peripheral nervous system involvement. We primarily investigated peripheral neuropathy with dorsal sural conduction study, which is a new method for detection of early peripheral neuropathy, in B(12) deficiency with megaloblastic anemia. Conventional nerve conduction studies and tibial sensory-evoked potential (SEP) recording were also performed. Twenty-eight B(12)-deficient patients (15 male, 13 female, mean age 65.8 years) with megaloblastic anemia and 18 age- and sex-matched controls were included in the study. Although dorsal sural sensory nerve action potentials (SNAPs) were not recorded in 15 (54%) of 28 patients, only 9 (32%) of them were found to have polyneuropathy by conventional conduction studies. Furthermore, patients with dorsal sural SNAP had mean lower amplitude, mean longer latency, and slower velocity response when compared with controls. Twenty patients (71%) were diagnosed as having myelopathy by the combination of tibial SEP and neurological findings. Two patients whose dorsal sural SNAPs were not recorded had normal tibial SEP responses; therefore, these patients were considered to have isolated peripheral neuropathy. As a result, we conclude that dorsal sural nerve conduction study is a reliable method for detection of early peripheral neuropathy in B(12) deficiency.