Parapsoriasis

By Shinjita Das, MD, Clinical Instructor;Physician, Department of Dermatology, Harvard Medical School;Massachusetts General Hospital

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Parapsoriasis refers to a group of skin diseases characterized by maculopapular or scaly lesions.

Parapsoriasis describes a poorly understood and poorly distinguished group of diseases that share clinical features. Parapsoriasis is not related to psoriasis; it is so-called because the scaly plaques sometimes appear similar.

There are 2 general forms:

Small-plaque type: Usually benign
Large-plaque type: A precursor of cutaneous T-cell lymphoma (CTCL)

Small-plaque parapsoriasis transforms into CTCL extremely rarely. Large-plaque parapsoriasis transforms into CTCL in about 10% of patients per decade.

Symptoms and Signs

The plaques are usually asymptomatic; their typical appearance is thin, scaling, dull, pink patches and plaques with a slightly atrophic or wrinkled appearance. In contrast, the plaques in psoriasis are well-demarcated and pink with thicker silvery scale.

Small-plaque parapsoriasis is defined by lesions < 5 cm in diameter, whereas large-plaque parapsoriasis has lesions > 5 cm in diameter.

Sometimes digitate plaques develop along the dermatomes, especially on the flanks and abdomen, in small-plaque parapsoriasis. Although digitate plaques of parapsoriasis may be > 5 cm, transformation into CTCL is extremely rare in small-plaque parapsoriasis.