Parakeratosis pustulosa - a distinct but less familiar disease

Introduction

Parakeratosis pustulosa (PP) is predominantly seen in children as an eczematoid eruption adjacent to the free margin of nail, extending to the dorsal nail fold. Hyperkeratosis under free margin of nail results in lifting up of the nail plate and causes deformity resembling a gaping toecap separated from the sole at the seam. Finger nails are affected more commonly than the toe nails with pitting, cross ridging of the nail plate occasionally.[1] This entity was described initially by Sabouraud in 1931 as ′parakeratosa microbienna du about des doigts′.[2] Brocq reported similar subungual changes and described the entity as ′parakeratosis psoriasis formes.[3] While reporting a large series of these patients, Hjorth and Thompsen stressed that this entity is not adequately described in literature and is often overlooked with varying diagnoses such as psoriasis, eczema, acrodermatitis, atopic dermatitis etc.[4] As far as ascertained, this condition is not described in Indian literature and hence we felt it important to report this less familiar disease seen recently by us.

Case Report

A 7 - month -old female baby was brought to the Dermatology OPD with complaints of nail deformity and thickened scaly patches adjacent to the nail plates of left hand and right great toe. According to her mother, the problem started initially with scaling and gradual thickening of skin without any pustular eruption. It subsided after treatment with topical and systemic medication such as emollients, antibiotics, antimycotics etc, but only to recur after some time. No history of applying cosmetics such as nail polish at the affected sites could be obtained. The child had the habit of thumb sucking. The elder male sibling was normal and family history was non contributory.

Dermatological examination of the hands revealed eczematous scaly patches over the skin adjacent to the affected nails. Onychomadesis (proximal separation) with erythema and ragged cuticle over the left index finger nail and leuconychia and friability of the left middle finger and longitudinal ridge in the nail plate of left index finger was seen [Figure - 1]. The great toe nail plate of right foot showed thinning with lateral onycholysis and erythema of proximal nail fold [Figure - 2]. The nail bed and hyponychium of the affected nail were normal although the nail folds were erythematous and non-tender. The cuticles were ragged and absent at places. Subungual hyperkeratosis under the free margins of nails and ridging with fine pitting was seen at few sites. Potassium hydroxide examination of both the skin scrapings and nail clippings showed no evidence of fungal infection. Routine haematological and biochemical investigations were within normal limits and bacterial culture was sterile. Roentgenogram of hands and feet were normal.

Histopathology of the lesion revealed hyperkeratosis, parakeratosis, mild acanthosis, and papillomatosis with infiltrate around the dilated blood vessels.

The parents were counselled to stop thumb - sucking habit of the baby and advised to apply topical emollients only, which resulted in marked improvement of the condition within two weeks period.

Discussion

The patient reported herein is diagnosed as a case of PP because of the characteristic eczematous scaly patches involving the skin adjacent to the nail plates. This is further supported by the fact that no infectious organism could be isolated from the site and the histology was consistent with the diagnosis of PP as described by Dulanto et al.[5]

The clinical features of PP were summarized by Hjorth and Thomsen in 91 cases and they stressed that this problem should be considered as a distinct clinical entity.[4] It presents commonly with scaly patches over the hands specially the thumb and index fingers, while on the feet the great toes are most commonly involved. Majority of the patients are young children with girls being affected more commonly than the boys.[4] Pustular eruption may be seen in some cases although such a history could not be obtained in our patient.

The course of PP is protracted and recurrences are the rule even after apparent and long peroids of cure. No specific therapy has been advocated for this condition. Stopping the thumb sucking habit and application of emollients improved the condition in our patient.

This entity needs to be differentiated from acrodermatitis of Hallopeau, pustular psoriasis, contact dermatitis, atopic dermatitis, tinea pedis, paronychia and dry fissured eczematoid dermatitis.b Pustules in parakeratosis pustulosa are rare and only seen in the initial stage, in contrast to pustular psoriasis or acrodermatitis of Hallopeau. The characteristic histopathology of psoriasis can urther confirm the diagnosis. Atopic dermatitis of the hands may cause nail deformity such as cross ridging due to the involvement of proximal nail fold. In addition, children with this disease usually have a flexural patch over the dorsum of histopathology reveals acute spongiotic dermatitis with eosinophils in dermal infiltrate. Dry fissured eczematoid lesions over the medial margin of the big toe and adjoining part of the feet may be seen in children with ichthyosis. This condition is usually bilateral and occurs in families. Tinea pedis shows maceration, scaling, occasional vesiculation, fissuring and the scrapings with KOH show fungal hyphae. Paronychia may be acute or chronic with signs of inflammation of the nail folds and etiological agents such as Staphylococcus aureus, Streptococcus pyogenes, Pseudomonas, Proteus species, anaerobes or Candida albicans may be isolated.

PP is rather a common but less known dermatological disorder in pediatric group with characteristic clinical features and must be considered as a separate entity. Atypical case can be recognized at a glance but anyone not acquainted with the clinical features may be tempted into a wrong diagnosis resulting in unnecessary medication. This is underscored by the absence of reported cases in Indian literature suggesting that this not so uncommon disease may have been wrongly typed in many instances.