Abstract

A 22-year-old woman presented with progressive sensory ataxia and optic neuropathy. Previous investigation by her general practitioner had found a low serum vitamin B₁₂, which had been corrected with oral supplementation. Neurological investigations showed raised plasma homocysteine and methylmalonic acid towards the upper limit of normal with a low serum vitamin B₁₂. MRI showed an extensive cord lesion in keeping with subacute combined degeneration of the spinal cord. We treated her with high dose parenteral vitamin B₁₂ and she has made a partial recovery. We discuss the management of patients who present with neurological manifestations of vitamin B₁₂ deficiency; highlighting the fact that parenteral replacement is needed in such cases, even if the serum vitamin B₁₂ level appears to be normal. We also discuss ancillary investigations that should be performed in patients with suspected vitamin B₁₂ deficiency.