Extra-Palmoplantar Lesions of Palmoplantar Pustulosis: Underrecognized but Important Manifestation

Patients with palmoplantar pustulosis (PPP) rarely develop scaly erythematous and/or pustular lesions on sites other than the palms and soles, such as the dorsa of the feet, lower legs, knees, elbows, buttocks and trunk.

This study aims to evaluate the characteristics of extra-palmoplantar lesions of Japanese patients with PPP.

Twenty-three patients (seven males and 16 females) with PPP and extra-palmoplantar lesions were examined.

The extra-palmoplantar lesions were classified into scaly, erythematous lesions (chronic type) (n = 15) and pustular lesions surrounded by erythema (acute type) (n = 8). In cases of acute exacerbation, multiple solitary pustules with or without scaly erythema developed following infection such as upper respiratory tract infection, tonsilitis, sinusitis and appendicitis. The frequency of joint manifestations was significantly higher in patients with acute type, as compared with chronic type (75.0% vs 13.3%). The histopathological features of scaly erythemas were focal parakeratosis, mild irregular acanthosis of the epidermis and mild mononuclear cell infiltration in the upper dermis, whereas Munro's microabscess was not observed in any cases. In contrast, a histopathological feature of the pustular lesion was consistent with that of pustular psoriasis. Expression of S100 family alarmin, CCL20 and CCR6 interaction and IL-36 was upregulated in the extra-palmoplantar lesional skin of PPP.

Alarmins triggered by mechanical stimuli induced extra-palmoplantar lesions of PPP, via CCL20/CCR6 interaction and IL-36. Extra-palmoplantar lesions can occur on pre-existing scars, in which tissue-resident memory T cells may be activated by mechanical stimuli and induce inflammatory cytokines.