Interdigital psoriasis of the feet (psoriasis alba): not a distinct form of psoriasis

Interdigital psoriasis (IP) of the feet is often missed and is commonly mistaken for interdigital fungal infection.

To assess the characteristics and the clinical presentation of IP, in order to better understand if IP should be considered a distinct form of psoriasis or not.

We performed a 1-year observational study on 164 psoriatic patients, affected by moderate to severe cutaneous psoriasis and undergoing systemic therapy, examining each patient between the digits of both feet. In every suspected case of IP, differential diagnosis with interdigital fungal infection was excluded by direct microscopic examination of skin scrapings, by culture and by skin biopsy.

We suspected IP in 7 of the 164 patients. IP was confirmed in 6 patients and in the other one a diagnosis of tinea pedis was made.

IP proved to be not rare or atypical since IP localized between the toes usually presents as characteristic whitish and sodden plaques or patches. Such a diagnosis should be considered in all patients presenting characteristic lesions especially if these have a negative fungal culture, are resistant to antimycotic treatment and involve patients with a history of psoriasis.