In which clinical scenario, after giving folic acid, neuropathic features stas worsening?

Vitamin B12 Major role in providing cofactors that are required to form myelin. Required for the production of methionine (precursor for S-adenosyl methionine), which is required for methylation reaction. Myelin maintenance and nerve function. Demyelination occurs from vitamin B12 deficiency. Neurological problems occur in most people who are deficient in Vitamin B12. Folic acid also masks the underlying disease, and allow the development or progression of neurological deterioration, if diagnosis depended on the presence on anaemic symptoms.