Casal's Necklace and Niacin Deficiency
Casal's necklace is pathognomonic for niacin (vitamin B3) deficiency, also known as pellagra—the answer is C. Niacin. 1, 2
Clinical Presentation
Casal's necklace represents the characteristic dermatitis of pellagra, manifesting as a pigmented, scaling rash that forms a distinctive ring around the neck in sun-exposed areas. 3, 4 This is part of the classic "4 Ds" of pellagra:
- Dermatitis: Photosensitive rash in sun-exposed areas, including the characteristic necklace distribution around the neck 3, 5, 6
- Diarrhea: Gastrointestinal manifestations 3, 4
- Dementia: Neuropsychiatric symptoms ranging from irritability and poor concentration to frank psychosis in advanced cases 5, 7
- Death: If left untreated 2, 3
Why Not the Other Options
Vitamin A deficiency (Option A) presents with night blindness and xerophthalmia, not Casal's necklace. 1
Vitamin C deficiency (Option B) causes scurvy with perifollicular hemorrhages and gingival bleeding, not the photosensitive dermatitis seen in pellagra. 1
Thiamine deficiency (Option D) causes beriberi and Wernicke-Korsakoff syndrome, characterized by neurological symptoms without the characteristic dermatitis of pellagra. 1
High-Risk Populations
Be vigilant for niacin deficiency in:
- Chronic alcoholics: The most common at-risk group in developed countries 5, 7, 6
- Maize-dependent populations: Especially without niacin fortification 2, 3
- Malabsorptive states: Including prolonged diarrhea 2
- Restrictive diets: Such as cassava-based diets or severe malnutrition 4
Treatment
Administer nicotinamide 100 mg three times daily (300 mg total) for 3 weeks, with maximum daily dose not exceeding 600 mg. 2 Alternative physiological dosing includes nicotinic acid 15-20 mg/day or nicotinamide 300 mg/day. 2
- Use the oral/enteral route whenever the gastrointestinal tract is functional 2
- Continue treatment for the full 3-week course even after symptom improvement 2
- Combine with a high-protein diet to address concomitant nutritional deficiencies 6
Clinical Pearls
The diagnosis is primarily clinical based on the characteristic dermatitis pattern. 4 Blood or tissue NAD levels may be measured, though a pragmatic approach is storing a blood sample and awaiting response to niacin supplementation. 2 The dramatic response to niacin therapy—with progressive resolution of dermatitis, diarrhea, and neuropsychiatric symptoms—essentially confirms the diagnosis. 4
Niacin can be synthesized from tryptophan (60 mg tryptophan produces 1 mg niacin), a pathway requiring thiamine, riboflavin, and pyridoxine. 1 This explains why pellagra is often a multiple vitamin-deficiency disease requiring comprehensive nutritional assessment. 6