Pellagra
A systemic disease caused by a severe deficiency of Niacin (Vitamin B3) or its precursor, tryptophan. It is classically defined by the “4 Ds”.
The “4 Ds” of Pellagra
- Dermatitis: Photosensitive, symmetric eruption (e.g., Casal necklace).
- Diarrhea: Often accompanied by other gastrointestinal distress (glossitis, stomatitis).
- Dementia: Neuropsychiatric symptoms including confusion, anxiety, and depression.
- Death: The final consequence if the condition remains untreated.
Key Clinical & Exam Features
| Feature | Description |
|---|---|
| Casal Necklace | Hyperpigmented, scaly band around the lower neck; a pathognomonic sign. |
| Etiology | Malnutrition, alcoholism, carcinoid syndrome (metabolizes tryptophan), or Hartnup disease. |
High-Yield Exam Pearl:
- Photosensitivity: The dermatitis occurs primarily in sun-exposed areas (sun-exposed face, neck, and dorsal hands).
- Carcinoid Syndrome: If an exam case describes a patient with flushing, diarrhea, and a skin rash, consider Pellagra caused by tryptophan diversion for serotonin production in carcinoid tumors.