Palmoplantar keratoderma, Bothnian type (PPKB) is one of the non-epidermolytic palmoplantar keratoderma. PPKB was initially reported to be prevalent in the north of Sweden, along the Gulf of Bothnia. The clinical characteristics of PPKB include diffuse, homogeneous, and even palmoplantar hyperkeratosis with swollen stratum corneum, which distinctively exhibits a whitish spongy appearance upon exposure to water. PPKB is the autosomal-dominant disorder caused by mutations in the aquaporin 5 gene, AQP5.
