Vitamin B6 (Pyridoxine) Deficiency
Neurology
Illness script · Neurology
Vitamin B6 (Pyridoxine) Deficiency
Deficiency of pyridoxine, a PLP-dependent cofactor for neurotransmitter synthesis and transamination, causing neuropathy, dermatitis, and sideroblastic anemia.
This illness script for Vitamin B6 (Pyridoxine) Deficiency covers predisposing factors, classic presentation, mechanism, workup, management, and the clinical pivots that separate it from look-alikes—written for USMLE Step 1 and clerkship reasoning.
01
Predisposing factors
- Isoniazid (INH) use — most classic drug cause; inhibits pyridoxal kinase and complexes PLP
- Alcoholism — poor intake plus impaired phosphorylation of B6
- Oral contraceptive use and hydralazine/penicillamine therapy
- Pregnancy and lactation (increased demand)
- Malnutrition, elderly, and patients on chronic hemodialysis
- Infants fed unsupplemented formula (B6-dependent seizures)
02
Presentation
- Peripheral neuropathy: symmetric sensory > motor, stocking-glove distribution
- Seborrheic dermatitis, glossitis, angular cheilitis (mucous membrane triad)
- Sideroblastic anemia: microcytic, hypochromic with basophilic stippling
- Seizures refractory to standard anticonvulsants (classic in infants and INH toxicity)
- Depression, confusion, irritability from impaired neurotransmitter synthesis
- INH toxicity triad: peripheral neuropathy + seizures + lactic acidosis
03
Pathophysiology
- Pyridoxine → pyridoxal-5-phosphate (PLP), the active coenzyme form
- PLP is cofactor for >100 reactions: transamination, decarboxylation, neurotransmitter synthesis (GABA, serotonin, dopamine)
- GABA deficiency lowers seizure threshold — key mechanism of INH/B6-deficiency seizures
- PLP required for ALA synthase in heme synthesis → deficiency causes ringed sideroblasts (iron trapped in mitochondria)
04
Diagnostics
- Plasma pyridoxal-5-phosphate (PLP) level — gold standard; low confirms deficiency
- CBC + peripheral smear: microcytic/hypochromic anemia with ringed sideroblasts
- Bone marrow biopsy: ringed sideroblasts (≥15% of erythroid precursors) — definitive for sideroblastic anemia
- Elevated homocysteine (PLP cofactor for transsulfuration pathway)
- Clinical diagnosis often made in INH-exposed patients with seizures + neuropathy
05
Management
- Pyridoxine (B6) 50–100 mg/day PO for deficiency-related neuropathy/dermatitis
- Always co-prescribe pyridoxine 25–50 mg/day with INH to prevent neuropathy
- INH-induced seizures: IV pyridoxine gram-for-gram equal to INH ingested dose (up to 5 g)
- B6-dependent epilepsy in infants: IV pyridoxine — dramatic seizure cessation is diagnostic
- Address underlying cause: alcohol cessation, stop offending drug, improve diet
06
Clinical pivots
How to separate this script from the look-alikes that show up on exams and on the wards.
Vitamin B12 Deficiency
B12 causes macrocytic megaloblastic anemia + subacute combined degeneration; B6 causes microcytic sideroblastic anemia.
Pellagra (Niacin/B3 Deficiency)
Pellagra presents with the 3 Ds (dermatitis, diarrhea, dementia); B6 deficiency has peripheral neuropathy and sideroblastic anemia instead.
Riboflavin (B2) Deficiency
B2 deficiency shares glossitis and cheilitis but lacks peripheral neuropathy, seizures, and sideroblastic anemia.
Lead Poisoning
Lead poisoning also causes sideroblastic anemia with basophilic stippling but has exposure history, encephalopathy, and elevated blood lead level.
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Educational use only. This illness script is a study framework, not medical advice. Confirm decisions with current guidelines and your clinical supervisors.