Background  Palmoplantar pustulosis (PPP) is a chronic and intensely inflammatory skin disease with pustules, erythema and scaling localized to the palms and soles. Pompholyx is characterized by recurrent crops of vesicles on the lateral aspects of the fingers and the palms and soles. Because both PPP and pompholyx share similar clinical and histological features, it is difficult to differentiate between these two diseases even for dermatologists.

Objective  To compare the histological features of PPP and pompholyx and to analyse their clinical characteristics.

Methods  The clinical history from 45 patients with PPP and 42 with pompholyx was evaluated. Among these patients, the punch biopsies from acute lesions of 40 PPP patients and 35 pompholyx ones were analysed, blind to the clinical diagnosis.

Results  There was no sexual predilection in either group, and 65.5% of PPP patients had smoking history. About half of the patients had concomitant palmoplantar lesions in PPP and pompholyx respectively. In histological evaluation, loss of granular layer, suprapapillary plates thinning, eosinophils in the pustules or vesicles, tortuous capillaries, capillaries touching the undersurface of epidermis and extravasated erythrocytes were statistically significant features of PPP. Confluent parakeratosis, psoriasiform epidermal hyperplasia, clubbing and anastomosing of the rete ridges favoured PPP. Meanwhile, multiple foci of parakeratosis, irregular epidermal hyperplasia and thinning of rete ridges were more often observed in pompholyx. However, dyskeratotic cells, papillary dermal oedema, dilated capillaries and acrosyringium were not significantly different between the two diseases.

Conclusions  Several histological features could serve as useful ‘clues’ to differentiate between PPP and pompholyx.