Sensory-motor polyneuropathy occurring in variant maple syrup urine disease.

[pyruvate dehydrogenase deficiency]

Maple syrup urine disease (MSUD ; OMIM 248600 ) results from an inherited deficiency of the branched-chain ketoacid dehydrogenase (BCKD ) complex . Approximately 20 % of patients with BCKD deficiency are non-classic variants of MSUD with differing clinical severity . Outcomes for this cohort are generally favourable ; episodes of metabolic decompensation do not appear to correlate with adverse events if acute management is promptly provided . A case of predominantly axonal sensory -motor neuropathy following metabolic decompensation which persisted for a number of months is presented in an adolescent girl with variant (intermediate type ) MSUD . EMG and nerve conduction studies suggested a pre-existent asymptomatic chronic neuropathy , exacerbated by the acute decompensation . Peak leucine concentration at decompensation was 1083 μmol /L . The patient had laboratory signs of secondary mitochondrial respiratory chain dysfunction at presentation . She had been on a moderate dose of thiamine prior to decompensation ; thiamine and pyridoxine blood concentrations were normal . This , to our knowledge , is the first report of a neuropathy presenting in a patient with a decompensation of variant MSUD . We propose that this presentation resembles the intermittent neuropathy observed in pyruvate dehydrogenase deficiency and may reflect secondary inhibition of pyruvate dehydrogenase activity by MSUD metabolites .