Casal's paint necklace is caused by

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