This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Dermatitis, Subject name: Dental
Casal's paint necklace is caused by 
Select and explain. 
A. Pellagra, B. SLE, C. Lichen planus, D. Pernicious anemia
A: Pellagra
Answer: A: Pellagra 
Explanation: Pellagra is characterised by deficiency of tryptophan, leading to photosensitivity on exposure to uv light three D'sof pellagra diarrhoea dermatitis dementia some impoant cutaneous features gauntlet of pellagra-sun burn over Dorsum of hands castles necklace- dermatitis over neck extending to anterior chest. cheliosis scarlet glossitis and stomatitis Ref Harrison20th edition pg 1345