Neurologic and evoked potential abnormalities in subtle cobalamin deficiency states, including deficiency without anemia and with normal absorption of free cobalamin
D. S. Karnaze and R. Carmel
Department of Neurology, University of Southern California, Los Angeles.
The meaning of a low serum cobalamin level when the classic findings of
pernicious anemia are lacking is undergoing reevaluation. We therefore
studied the neurologic status of 11 patients who had low cobalamin levels
without definite hematologic evidence of deficiency. Neurologic evaluation
included pattern-shift visual and median and posterior tibial nerve
somatosensory evoked potentials. None of the patients had megaloblastic
changes in the blood or bone marrow, although 7 of the 11 had subtle
cellular cobalamin disturbances demonstrated by an abnormal deoxyuridine
suppression test result. Seven patients had normal Schilling test results
and 2 had borderline results; however, 2 of the 5 patients tested further
had food-cobalamin malabsorption, while a third had prepernicious anemia.
The patients displayed a variety of neurologic problems, including
dementia, depression, myelopathy, neuropathy, and seizure disorder; 1
patient was neurologically normal by clinical criteria. Evoked potential
abnormalities were demonstrable in 8 of the 9 patients with subtle
cobalamin deficiency, and in at least 5 cases the disturbance was central.
In contrast, both patients whose low serum cobalamin levels were found on
evaluation to be spurious had normal evoked potentials. Evoked potential
abnormalities improved in the one patient retested after cobalamin therapy.
These findings demonstrate that neurologic deficits occur not only in
classic cobalamin deficiency but also in subtle or atypical cobalamin
deficiency states in which anemia is absent and Schilling test results are
normal. Electrophysiologic evidence of neurologic impairment is often
present, even in patients without obvious clinical neurologic
abnormalities.
