🔑 Key Learning

  • Pellagra is caused by a deficiency of vitamin B3 (niacin) or its precursor tryptophan
  • Presents with the classical "3 Ds": Dermatitis, Diarrhoea, Dementia
  • Casal’s necklace is a classic dermatological finding (photosensitive dermatitis around the neck)
  • Management includes niacin supplementation, dietary modification, and treatment of underlying causes (e.g. alcoholism, malabsorption)

🧬 Pathophysiology

  • Niacin (vitamin B3) deficiency due to:
    • Inadequate dietary intake
    • Low tryptophan (niacin precursor)
  • Impaired synthesis of NAD and NADP, which are essential coenzymes in energy metabolism
  • Tissues with high energy requirements (skin, gut, CNS) are most affected

👀 Clinical Features – "3 Ds"

  • Diarrhoea: often persistent, may lead to malnutrition or dehydration
  • Dementia: confusion, memory loss, hallucinations, psychosis
  • Dermatitis:
    • Symmetrical, scaly, erythematous rash in sun-exposed areas
    • Classically affects neck – called Casal’s collar
Pellagra
Figure 6: Pellagra. Center for Disease Control and Prevention. 

          

đź’Š Management

  • Niacin supplementation:
    • Oral or IV nicotinamide (niacinamide) or nicotinic aci
  • Treat underlying causes:
    • Dietary: Increase intake of niacin-rich foods: meat, poultry, fish, peanuts, fortified cereals
    • Alcoholism, malabsorptive conditions (e.g. Crohn’s, carcinoid syndrome), isoniazid 

đź“ť Exam Clues & Clinchers

  • "Diarrhoea, dementia, dermatitis" in context of poor diet or alcohol dependence → Pellagra
  • "Photosensitive rash around the neck" → think Casal’s collar
  • Isoniazid or carcinoid syndrome in stem? → impaired niacin metabolism
  • Responds rapidly to vitamin B3 replacement