🧣 TOACS FCPS Station · Casal Necklace in Pellagra
📷 Clinical Photograph – Casal Necklace
🔍 Key clinical features:
- ✓ Symmetric, photosensitive rash – around the neck and upper chest
- ✓ Well-demarcated, erythematous, hyperpigmented plaques
- ✓ Classic "Casal necklace" – collar-like distribution
- ✓ Part of pellagra triad – Dermatitis, Diarrhea, Dementia
- ✓ Sun-exposed areas – also affects hands (glove distribution), feet (stocking), and face
📋 Clinical scenario (examiner prompt)
A 10‑year‑old child from a rural area where maize (corn) is the staple food is brought with a photosensitive rash around the neck, chest, and dorsal hands. The mother reports that the child has had chronic diarrhea and has become confused and irritable over the past few weeks. On examination, the rash is symmetric, well‑demarcated, erythematous, and hyperpigmented in a collar‑like distribution around the neck (Casal necklace). The dorsal hands show a similar rash. The child appears malnourished and has a beefy red tongue.
🧑⚕️ Examiner tasks · TOACS
1. Identify the diagnosis from the clinical image and context.
2. Describe the clinical features (Casal necklace, photosensitive dermatitis, diarrhea, confusion, beefy red tongue).
3. Explain the underlying deficiency (niacin/Vitamin B3 deficiency, pellagra, tryptophan conversion).
4. Discuss management (nicotinamide supplementation, B-complex, sun protection, dietary improvement).
🎯 Expected answers (for examiners)
- • Diagnosis: Pellagra (niacin/Vitamin B3 deficiency)
- • Clinical features: Casal necklace (photosensitive rash on neck/upper chest), symmetric dermatitis on sun-exposed areas (dorsal hands/feet), diarrhea, dementia (confusion/irritability), beefy red tongue (glossitis), cheilosis
- • Pathophysiology: Niacin (or tryptophan) deficiency → reduced NAD/NADP → impaired cellular metabolism, skin photosensitivity, GI symptoms, and CNS dysfunction
- • Risk factors: Maize-based diets (niacin bound as niacytin), Hartnup disease, carcinoid syndrome, isoniazid therapy, anorexia nervosa
- • Treatment: Nicotinamide (niacinamide) 50-300 mg/day PO (preferred to avoid flush). If severe, IV 100 mg. B-complex vitamins, sun protection, dietary improvement
- • Prognosis: Excellent with prompt treatment – skin improves within days, neurologic symptoms over weeks
• Location: Neck and upper chest (collar-like distribution)
• Appearance: Well-demarcated, erythematous, hyperpigmented, photosensitive plaques
• Pathognomonic for pellagra (niacin deficiency)
• Associated with: 3 D's – Dermatitis, Diarrhea, Dementia
• Treatment: Nicotinamide (50-300 mg/day) + B-complex
• Prevention: Niacin-rich diet or fortified foods (maize nixtamalization)
⚡ Quick FCPS‑style MCQ
A child from a maize-based diet area presents with a photosensitive rash around the neck (Casal necklace), chronic diarrhea, and confusion. The most likely diagnosis is:
A. Kwashiorkor B. Pellagra (niacin deficiency) C. Scurvy D. Beriberi📌 Topic summary · Casal Necklace in Pellagra
Photosensitive rash on neck/upper chest
Niacin (Vitamin B3) deficiency
Dermatitis, Diarrhea, Dementia
Nicotinamide 50-300 mg/day
Maize-based diet, Hartnup, INH, carcinoid
Photosensitivity (other causes)
| Feature | Pellagra (Niacin Deficiency) |
|---|---|
| Deficiency | Niacin (Vitamin B3) – also tryptophan malabsorption |
| Classic triad | Dermatitis (Casal necklace, glove/stocking), Diarrhea, Dementia (confusion, depression, delirium) |
| Casal necklace | Photosensitive, well-demarcated erythematous/hyperpigmented rash around neck and upper chest |
| Other manifestations | Beefy red tongue (glossitis), cheilosis, photosensitivity, peripheral neuritis |
| Treatment | Nicotinamide (niacinamide) 50-300 mg/day PO; IV 100 mg if severe; B-complex vitamins; sun protection |
| Differential | Other photosensitive rashes (lupus, drug-induced), zinc deficiency (acrodermatitis enteropathica) |