Polymorphic pityriasis rosea precipitating psoriasis

Abstract

Sir, Pityriasis rosea (PR) is an acute self limiting papulosquamous disorder characterized by a large erythematous herald patch and subsequent eruptions of multiple similar, smaller oval patches in the classic “Christmas tree” distribution. PR presents as predominantly papular, papulosquamous, vesicular, purpuric and lichenoid lesions. Several unusual variants have been reported in literature and constitute about 20% of all cases which might pose a diagnostic problem.[1] Psoriasis is a polygenic disease and has various triggering factors (stress, drugs, infections, alcohol etc) which may elicit a psoriatic phenotype in predisposed individuals.[2–4] A 45 year old male presented with asymptomatic raised red lesions on the face, trunk, upper limbs, palms and lower limbs since five days. There was history of sore throat two weeks prior to the onset of rash for which he did not seek treatment. There was no history of fever or intake of any medications. On examination, multiple bilaterally symmetrical erythematous papules and plaques were present on the face, flexor aspect of the forearms, legs and in a Christmas tree pattern over the back with few plaques having collarette scales. Erythematous papules were present on both the palms [Figure 1]. Multiple pustules, erythematous papules and plaques were distributed along the lines of cleavage over both the flanks [Figure 2]. Oral and genital mucosae were not involved. Routine investigations revealed no abnormality. ELISA for HIV and VDRL were non reactive. Tzanck smear from a pustule showed neutrophils and gram staining did not reveal any organisms. A skin biopsy from a scaly plaque showed parakeratosis and extravasation of RBC's suggestive of pityriasis rosea. Based on clinical presentation and histopathology, a diagnosis of pityriasis rosea with atypical presentation was entertained and patient was treated symptomatically with oral antibiotics and emollients. Subsequently the patient presented with exacerbation of lesions the following week. Examination revealed large scaly plaques replacing the previous lesions over both the flanks [Figure 3]. There was peeling of skin over palms. Repeat skin biopsy showed parakeratosis, acanthosis, Munro's micro abscess, spongiform pustule and papillary dermal extravasated RBC's extending into stratum spinosum [Figure 4]. These features were suggestive of both psoriasis and pityriasis rosea. Patient was treated with topical emollients and steroids. After one week there was significant resolution of lesions. Figure 1 Erythematous papules and plaques over palms Figure 2 Papules with collarette scaling and pustules Figure 3 Scaly plaques over right flank (second visit) Figure 4 Extravasation of RBC's in the dermis extending into stratum spinosum, with micro munro abscess In this case, we would like to highlight the following features. Firstly, the patient had unusual polymorphic papular, papulosquamous and pustular lesions of PR in a classical distribution along with involvement of atypical sites like face and palms. Coexistence of such multiple atypical lesions of PR in a single individual is rare.[5] Secondly, PR had precipitated psoriasis which is a very rare triggering factor and so far not reported. Psoriasiform lesions developed on PR lesions which was suggestive of an isotopic phenomenon where psoriasis was riding ‘piggy back’ on PR. Psoriasis lesions promptly resolved along with PR lesions. Hence, the possibility of psoriasis being precipitated by pityriasis rosea cannot be ruled out. We are reporting this rare case of polymorphic pityriasis rosea (classical as well as atypical lesions such as palmar, facial and pustular) precipitating psoriasis.