This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Social & Preventive Medicine
Casal's necklace is seen in deficiency of: September 2012 
Select and explain. 
A. Vitamin A deficiency, B. Niacin, C. Vitamin B12 deficiency, D. Iron deficiency anemia
B: Niacin
Answer: B: Niacin 
Explanation: Ans: B i.e. Niacin The Casal collar or Casal necklace is a clinical sign in which there is erythematous pigmented skin rash in the distribution of a broad collar (dermatomes C3 and C4). It is seen in patients with pellagra.