A case of revertant mosaic‐like normal‐looking spots in a patient with erythroderma with IL36RN and CARD14 heterozygous mutations

An 89‐year‐old Japanese woman presented with erythroderma associated with significant scaling. A histological examination showed acanthosis with hyperkeratosis and hyperkeratinization of the hair follicles. Genetic analyses using DNA from the peripheral blood revealed heterozygous mutations in IL36RN (c.115+6T>C) and CARD14 c.2648G>A (p.Arg883His). Based on these findings, we diagnosed her with erythroderma attributable to autoinflammatory keratinization disease. She then developed more than 30 small, round, well‐defined, spots on her back and extremities that appeared histologically normal. We suspected that these spots might be revertant mosaicism. Immunohistochemical staining with p65, which is a component of nuclear factor kappa‐light‐chain‐enhancer of activated B cells (NF‐kB), revealed nuclear staining in epidermal keratinocytes in erythematous lesions, but not in the normal‐looking spots. However, mutations in IL36RN and CARD14 unexpectedly persisted in the epidermis and dermis of the normal‐looking spots.