INTRODUCTION

Psoriasis is a chronic inflammatory condition. It usually manifests as erythematous, scaly patches with a predilection for the elbows, knees, extensor extremities, scalp, and lumbosacral regions. There are several clinical features that may lead to diagnostic confusion in some situations. Annular morphology is a rare presentation of this disease and must be differentiated on a clinical/pathological basis from other diseases that usually produce annular lesions. Herein, we report the case of a child who presented with atypical, mainly annular, hypopigmented lesions of psoriasis present since the age of twelve years.

CASE REPORT

A twelve-year-old boy, with no notable pathological history, consulted for diffuse, pruritic, erythematous, scaly lesions on the body that had been evolving for eight months in flare-ups and remissions, for which he had applied several topical treatments, notably antimycotics, without any improvement. He reported that the lesions had had this clinical appearance since the beginning. There was no notion of pustular lesions, nor of pustules or scaling reminiscent of pre-existing pustules. On clinical examination, the child was in good general condition with multiple, silvery, erythematous plaques with scaly surfaces and hypopigmented centers, located preferentially on the axillary folds, trunk, and lower limbs, sparing the face (Figs. 1a and 1b). Broq’s methodical scraping was positive, Wood’s light was negative, and the rest of the clinical examination was unremarkable. A skin biopsy (Fig. 2) confirmed the diagnosis of psoriasis and the patient was initiated on methotrexate with improvement.

	Figure 1: (a) Multiple annular plates with centrifugal extension at the trunk level. (b) Multiple annular scaly patches on the lower limbs.
	Figure 2: Histological section showing a typical aspect of psoriasis.

DISCUSSION

Psoriasis in children may present with several clinical presentations, including typical plaques, guttate, inverted, palmoplantar, linear, and seborrheic forms [1,2], among which plaque psoriasis is the most common. The annular form has been described in the literature as a resolution of plaques following inadequate treatment or as a presentation of pustular psoriasis [3]. Primary non-pustular, annular, psoriatic plaques have been mentioned in some reports. In a review of 1262 children with psoriasis, Morris et al. [4] mentioned a type of non-pustular annular psoriasis. Abel et al. [5] explained that the central parts of some psoriatic plaques may involute after topical treatment and, as a result, transient circular lesions form. Guill et al. reported two cases with such a clinical presentation and typical psoriatic histopathology [6]. Terunuma et al. described an acute annular psoriatic rash with histology showing the presence of psoriatic changes yet no pustules, in contrast to annular pustular psoriasis [7]. Primary plaque psoriasis, which is exclusively annular, has been rarely described in the literature, and our case had a de novo presentation with lesions characteristic of plaque psoriasis, yet with a distinct central clearing and an annular pattern of the plaques. This was unusual as the plaques were consistently annular and not the result of any previous treatment. Annular plaque psoriasis has a broad differential diagnosis and may be confused with other entities, such as dermatophyte of glabrous skin, pityriasis rosea, subacute cutaneous lupus erythematosus, centrifugal erythema annulare, hypopigmented vitiligo, granuloma annulare, serpiginous perforating elastosis, sarcoidosis, nummular eczema, and urticaria [8]. These entities may be distinguished on the basis of histopathological findings. Although a rare entity, primary ring psoriasis occurs in all ages, yet affects a relatively higher proportion of the younger population. It has a more benign course than pustular psoriasis, which may be accompanied by fever and leukocytosis or even general impairment. Complete resolution with treatment usually occurs within days to weeks yet may take several months [9].

CONCLUSION

This case highlights a rare presentation of a highly common condition and shows that psoriasis may be retained in the differential diagnosis of annular plaques.

REFERENCES

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