Nagashima palmoplantar keratosis (NPPK) is a rare nonsyndromic genetic dermatosis that was first described in 1977. The disease affects both sexes equally and almost exclusively affects people of Asian ethnicity. There is an estimated prevalence of 1.2:10 000 in Japanese populations and 3.1:10 000 in Chinese populations.

This condition has been linked to loss of function mutations in the serine protease inhibitor (serpin), class B, member 7 (SERPINB7) gene. Most cases demonstrate an autosomal recessive inheritance pattern, but autosomal dominant cases have been reported. The pathophysiological mechanism of this disorder remains poorly understood. However, it is hypothesized that mutation of the SERPINB7 gene leads to serine protease overactivity in the stratum corneum. This results in structural degradation of the epidermis, enabling transepidermal water permeation.

NPPK typically presents within the first year of life with a nonprogressive, erythematous, well-demarcated palmoplantar hyperkeratosis that extends to the dorsal surfaces of the hands and feet and often involves the area of the Achilles tendon. Involvement of the elbows and knees is not uncommon. Affected areas frequently demonstrate hyperhidrosis. On exposure to water, patients may report a whitish, spongy change to the lesions.

NPPK is frequently complicated by malodorous maceration with recurrent tinea infections. However, unlike other palmoplantar keratodermas (PPKs), individuals with NPPK usually only have mild hyperkeratosis. Moreover, they do not develop flexion contractures or constricting bands.