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Parakeratosis pustulosa with mycotic superinfection.

Herein we report a case of parakeratosis pustulosa (PP) manifesting as a subungual hyperkeratosis in an adult patient. In fact, parakeratosis pustulosa is a chronic dermatosis characterized by erythemato-squamous lesions affecting periungual skin with pitting and cross-ridging of the nails of one or more digits [1]. It was first reported in 1931 under the nomenclature “Parakératose microbienne du bout des doigts” [2]. However, Hjorth and Thomsen are the first to present this entity in English literature under the heading “parakeratosis pustulosa” [3].

The disorder affects mostly young girls under the age of five years. Thumb or middle finger is affected more often than the toes. The lesions begin near to the free edge of the nail as few pustules or vesicles in about 25% cases.[4] Pink or skin-colored and sharply delineated plaques are densely studded with scale [1]. In most cases, only the tips of digits are affected and the skin changes may extend on to the nail folds or dorsal side of the digits. The distal nail plate shows onycholysis usually at the corner. Though uncommon, subungual hyperkeratosis, when occurs, rarely extends beyond 1-2 mm into the nail bed. [4].

Histopathologic studies are sparse. Only three reports describe the histologic features similar to chronic eczema or psoriasis [5–7]. As early as 1974, de Dulanto et al. [5] reported the histology of one case and observed hyperkeratosis, parakeratosis, pustules, acanthosis, mild exocytosis, papillomatosis, and polymorpholymphocytic infiltrates. Later, Avci et al. [6] additionally noted many dyskeratotic cells in stratum spinosum. Pandhi et al. [7] also described hyperkeratosis, parakeratosis, mild acanthosis, and papillomatosis with infiltrate around the dilated blood vessels. These histologic features of hyperkeratosis, parakeratosis, mild acanthosis, papillomatosis, and polymorpholymphocytic infiltrate described in a few cases are nonspecific or similar to those seen in psoriasis or chronic eczema.

No specific therapy has been recommended. Though topical corticosteroids have been used in most reports, topical emollients remain the recommended mode of treatment [1]. Our patient was treated with terbinafine 250 mg per day in association with application urea 40% one month before introduction of Calcipotriol associated with Bethametasone with a good outcome (Fig. 1d).

In summary PP appears rare largely due to unfamiliarity and infrequent reporting in the literature. We suggest that PP should be considered as a distinct entity affecting the nail unit.

Ethic statement

A written informed consent was obtained from the patient for the publication of this case report and accompanying images. The authors have no ethical conflicts to disclose. The research was conducted ethically in accordance with the World Medical Association Declaration of Helsinki.