Quiz 17: What is your diagnosis?

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Diagnosis: Quiz 17

Quiz 17

Answer: Pityriasis rosea

Criteria for diagnosis histopathologically: The findings of a hyperplastic epidermis with mounds of parakeratosis and with foci of spongiosis in the spinous zone, in combination with a perivascular infiltrate of lymphocytes around dilated venules of the superficial plexus and extravasated erythrocytes there, are those of pityriasis rosea.

Differential diagnosis histopathologically: Histopathologic changes present in erythema annulare centrifugum cannot be distinguished from those of pityriasis rosea. In allergic contact dermatitis or nummular dermatitis, spongiosis is usually more prominent and epidermal hyperplasia is more pronounced. In pityriasis rosea, spongiosis occurs typically in foci, sometimes even spongiotic vesiculation is seen, while in other parts of the epidermis spongiosis is scant.

Criteria for diagnosis clinically: Oval, orange-to red-papules and plaques covered by a collarette of fine scales located on the trunk are characteristic of pityriasis rosea.

Differential diagnosis clinically: There is none. 

Clinico-pathologic correlation: The lesion is papular because of the hyperplastic epidermis and the inflammatory cell infiltrate in the papillary dermis. The scale is a consequence of parakeratosis. The typical orange-to-light red color is a result of dilated, erythrocyte-filled venules and of extravasated erythrocytes in the papillary dermis.

Options for therapy predicated on knowledge of histopathologic findings: Pityriasis rosea is a transient disease that is usually asymptomatic, therefore, no therapy is necessary.

1) In the majority of cases, pityriasis rosea can be diagnosed clinically, while the histopathologic findings are undistinguishable from those of erythema annulare centrifugum. In this patient, however, neither the clinical findings nor the histological findings are diagnostic by themselves and clinico-pathological correlation enables accurate diagnosis to be rendered.

2) Collarettes of scale represent the clinical correlate of residual mounds of parakeratosis that have been shed in the center. Spongiotic dermatitides with an accelerated turnover of keratinocytes manifest themselves histologically with spongiosis and later with mounds of parakeratosis that house globules of plasma. 

3) The lesions in this patient are early in the course of the disease because clinically the scale hardly is discernible, and histopathologically spongiosis dominates over the changes of epidermal hyperplasia and parakeratosis.

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