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What is Casal's necklace is a feature of? and explain in detail?
Ans. is 'b' i.e., Pellagra* The Casal collar or Casal necklace is a clinical sign in which there is an erythematous pigmented skin rash partly or completely encircling the lower part of the neck (dermatomes C3 and C4). It is seen in patients with pellagra.