Dermal Cystine Crystals: An Incidental Finding During Mohs Surgery.

Cystinosis is an autosomal recessive lysosomal storage disorder with intracellular cystine accumulation caused by mutations in the CTNS gene. We present a case of a 48-year-old woman with a history of cystinosis and squamous cell carcinoma treated with Mohs micrographic surgery where widespread deposition of cystine crystals were noted on frozen sections of the Mohs layers. These were rectangular to polygonal refractile crystals within the cytoplasm of dermal fibroblasts and macrophages which were highlighted by polarized light microscopy.