What is parapsoriasis?

The skin diseases included under this diagnosis are poorly understood and encompass a morass of confusing terms. The “splitters” have described over a dozen varieties of parapsoriasis, while the “lumpers” limit this designation to only a few types. This discussion supports the “lumpers” viewpoint.

Small-plaque parapsoriasis is characterized by chronic, well-marginated, mildly scaly, slightly erythematous, and round to oval skin lesions measuring <4 to 5 cm in diameter. The long axes of the lesions are arranged in a parallel configuration, and the lesions occur on the trunk and proximal extremities in a pityriasis rosea–like pattern. The lesions have been likened to fingerprints and reported under the descriptive term of digitate dermatoses. This form of parapsoriasis does not progress to lymphoma.

Large-plaque parapsoriasis presents as palm-sized or larger lesions located most frequently on the thighs, buttocks, hips, lower abdomen, and shoulder girdle areas (Fig. 46-2). The lesions may be pink, red-brown, or salmon-colored. They often have fine scale and show epidermal atrophy with cigarette-paper wrinkling. Some patients may have lesions with a netlike or reticular pattern with telangiectasia and fine scale. This clinical type of lesion is referred to as retiform parapsoriasis or poikiloderma atrophicans vasculare. Between 15% and 20% of patients with large-plaque parapsoriasis eventually develop mycosis fungoides.

Sehgal VN, Srivastava G, Aggarwal AK: Parapsoriasis: a complex issue, Skinmed 6:280–286, 2007.