Diffuse palmoplantar keratoderma, Bothnian type

Diffuse palmoplantar keratoderma, Bothnian type (also known as Bothnia-type PPK or keratoderma palmoplantaris diffusa, Bothnian type) is a rare inherited skin disorder characterized by diffuse thickening of the skin on the palms of the hands and soles of the feet (palmoplantar keratoderma). The condition was first described in families from the Bothnian region of northern Sweden. It is caused by mutations in the AQP5 gene, which encodes aquaporin 5, a water channel protein important for sweat gland function and skin hydration. The keratoderma typically presents in early childhood and is notable for a distinctive spongy, white appearance of the thickened skin, particularly when exposed to water or moisture (a feature sometimes described as 'transgrediens' or wet-spongy pattern). The skin thickening is generally symmetric and can cause discomfort, difficulty with manual tasks, and impaired quality of life. The condition primarily affects the integumentary system (skin), specifically the palms and soles, though the thickened skin may occasionally extend beyond these areas onto the dorsal surfaces of the hands and feet. Hyperhidrosis (excessive sweating) of the palms and soles is a commonly associated feature, which may exacerbate the spongy white appearance of the affected skin. There is no cure for Bothnian-type palmoplantar keratoderma. Treatment is symptomatic and supportive, focusing on regular use of emollients, keratolytic agents (such as urea-based or salicylic acid-based creams) to reduce skin thickness, and careful foot care to prevent secondary complications such as fungal infections. In some cases, mechanical debridement of thickened skin may be helpful. Genetic counseling is recommended for affected families.

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