Vitamin B12 deficiency.

Patients with subacute combined degeneration who smoked had significantly lowered plasma thiocyanate levels than control smokers, but plasma thiocyanate levels in non-smoking patients with neurological disease due to vitamin B1, deficiency were not significantly different from control values. The results provide no support for the hypothesis that chronic cyanide intoxication is responsible for the occurrence of neurological disease in a minority of patients with vitamin B1, deficiency, although they do not conclusively exclude this possibility. The association between smoking and subacute combined degeneration of the cord has been confirmed in this study but it remains unexplained.