110 Methylmalonic acid testing in neurological patients

Abstract

Vitamin B12 deficiency can lead to neurological abnormalities including paraesthesia, ataxia and subacute combined degeneration of the cord (SACD). Nitrous oxide abuse leads to SACD via func- tional B12 deficiency. Methylmalonic acid (MMA) testing is increasingly available, but it remains unclear where MMA levels are clinically useful.We performed a quality improvement project examining Vitamin B12 and MMA levels in a cohort of neu- rological patients. All patients known to neurology who underwent same-day testing of B12 and MMA levels (2016–2019) were included.60 individual patient records were evaluated. 17 individuals (28%) had high MMA, of whom 6 individuals had SACD and 11 had peripheral neuropathy. These patients had B12 levels between 91–371ng/L (lower limit of normal (LLN) is 197ng/L). Of these, only one had severe B12 deficiency, 4 had moderate deficiency (150–197ng/L) and 12 (71%) had normal B12. The highest B12 level associated with raised MMA was 372ng/L. All individuals with B12 >372ng/L and neurological symptoms had normal MMA.In individuals with serum vitamin B12 above the lower 1/3 of the reference range and neurological symptoms/signs, MMA does not add to the clinical picture. Furthermore, MMA testing does not change management in patients with B12 levels below the LLN, all of whom should be treated for B12 deficiency. We suggest testing MMA in those with Vitamin B12 levels in the lower 1/3 of the reference range.katieyoganathan@gmail.com