Overview
Recognise deficiency-related neuropathy, myelopathy, ataxia and encephalopathy, identify malabsorption and functional deficiency, and replace nutrients urgently without masking a second diagnosis or causing refeeding harm.
The nervous system depends on micronutrients for myelin, mitochondrial energy, neurotransmission and antioxidant defence. Deficiency therefore produces overlapping patterns rather than one symptom per vitamin. Tempo, diet, gastrointestinal anatomy, alcohol, medicines, recreational exposure and systemic clues identify the likely mechanism. Ask about bariatric or gastric surgery, ileal disease, coeliac disease, chronic diarrhoea, pancreatic or cholestatic disease, vegan diet, food insecurity, eating disorder, alcohol dependence, nitrous oxide and zinc-containing supplements or denture products.
B12 and copper deficiency both damage posterior columns and corticospinal tracts, causing impaired vibration and joint position, sensory ataxia, paraesthesia and spastic weakness. B12 can also cause neuropathy, optic disease and neuropsychiatric manifestations. Thiamine deficiency is an emergency when encephalopathy, eye signs or gait ataxia occurs. Vitamin E deficiency resembles a hereditary ataxia with large-fibre neuropathy. Niacin deficiency causes pellagra—photosensitive dermatitis, diarrhoea and cognitive or encephalopathic change—while folate deficiency more often produces haematological and fetal-neural-tube consequences than the classic B12 myelopathy.