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. There are 2 general forms: a small-plaque type, which is usually benign, and a large-plaque type, which is 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.
The plaques are usually asymptomatic; their typical appearance is thin, scaling, dull, pink patches and plaques with a slightly atrophic or wrinkled appearance. 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 may be > 5 cm, transformation into CTCL is extremely rare.
Treatment of small-plaque parapsoriasis is unnecessary but can include emollients, topical tar preparations or corticosteroids, phototherapy, or a combination. Treatment of large-plaque parapsoriasis is phototherapy (narrowband ultraviolet B [NBUVB]) or topical corticosteroids.
Course for both types is unpredictable; periodic clinical follow-up and biopsies give the best indication of risk of developing CTCL.
Last full review/revision October 2012 by Peter C. Schalock, MD