A case of revertant mosaic‐like normal‐looking spots in a patient with erythroderma with <scp><i>IL36RN</i></scp> and <scp><i>CARD14</i></scp> 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.