Digitate dermatosis (small-plaque parapsoriasis)
Published Web Locationhttps://doi.org/10.5070/D31xb3p8dn
Digitate dermatosis (small-plaque parapsoriasis)The Ronald O. Perelman Department of Dermatology, New York University School of Medicine, New York, New York
Jesse Lewin MD, Jo-Ann Latkowski MD
Dermatology Online Journal 18 (12): 3
We report a 79-year-old man with a 15-year history of elongated, finger-like, erythematous patches that are symmetrically distributed on his flanks and of small, <5 cm, erythematous, slightly scaly, round-oval patches on the upper and lower extremities. The lesions were occasionally pruritic and waxed and waned over the years. His clinical and histopathologic data indicated small-plaque parapsoriasis, which is a benign entity that has been the center of controversy over the years, owing to its similarities to large-plaque parapsoriasis, which is on a spectrum with mycosis fungoides.
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A 79-year-old man was referred to the New York University Dermatologic Associates with a 15-year history of faint, erythematous patches on his trunk, which were occasionally pruritic and that waxed and waned over the years. The patient noted improvement of his eruption with ambient light exposure while in Florida, but it always recurred. He denied constitutional symptoms, which included fever, chills, or weight loss.
Elongated, finger-like, erythematous patches were distributed symmetrically on flanks, and small, <5 cm, erythematous, slightly scaly, round-oval patches were present on upper and lower extremities. The patient had no cervical, axillary, or inguinal lymphadenopathy or hepatosplenomegaly.
Within the superficial dermis, there is a moderately dense, patchy, lichenoid and perivascular, predominantly mononuclear inflammatory cell infiltrate that is composed of lymphocytes with scattered histiocytes. There is a slight increase in thickness and eosinophilia of papillary dermal collagen bundles and slight homogenization of these bundles. Lymphocytes are present both along the dermoepidermal junction and, in foci, at higher levels of the epidermis. In addition, there are foci of epidermal spongiosis. The stratum corneum is ortho- and parakeratotic.
Digitate dermatosis is a variant of small-plaque parapsoriasis, which presents clinically with distinct, finger-like, digitate patches that typically are found on the flanks. Small-plaque parapsoriasis and large-plaque parapsoriasis were first described by Brocq in 1902 as parapsoriasis en plaques, which referred to round, well-circumscribed patches, 2-to-6 cm, that clinically resembled psoriasis . Over time, the classification of these entities has been refined and further elucidated by several authors, who subsequently separated small-plaque and large-plaque parapsoriasis. These authors confirmed that large-plaque parapsoriasis is more closely related to patch-stage mycosis fungoides [2, 3, 4].
Small-plaque parapsoriasis is characterized by a chronic, waxing and waning course early on, which often progresses slowly to a more persistent form. The patches and plaques, which are generally asymptomatic, or, at times, pruritic, favor the trunk and extremities, with more limited forms favoring sun-protected areas. Small-plaque parapsoriasis is more common in middle-aged and elderly individuals, with a peak in the 40- to 50-year-old range and a male predominance . Small-plaque parapsoriasis is differentiated from large-plaque parapsoriasis by the 5 cm rule, whereby lesions above 5 cm are considered to be of the large-plaque variety. Digitate dermatosis, which is a variant of small-plaque parapsoriasis that is demonstrated in our patient, defies this rule with elongated, finger-like patches, which often are symmetrically distributed on the flanks and at times measure over 10 cm in diameter .
The pathogenesis of small-plaque parapsoriasis has not been fully elucidated. However, it has been demonstrated that superficial cutaneous infiltrates of CD4+ T-cells predominate . Whereas dominant T-cell clonality has been demonstrated frequently in large-plaque parapsoriasis, it is noted less commonly in small-plaque disease [6, 7]. Whereas it has been estimated that the progression of large-plaque parapsoriasis to lymphoma is 10 percent per decade, small-plaque parapsoriasis has been classified by the World Health Organization as a benign disease that never evolves into mycosis fungoides .
When classic lesions of digitate dermatosis are present, the diagnosis of small-plaque parapsoriasis is essentially made by clinical appearance and history; a biopsy is not always necessary. When small-plaque parapsoriasis clinically appears to overlap with large-plaque parapsoriasis, that is, both larger patches and smaller patches are present, the diagnosis can be based upon clinical and histopathologic features. Lesions of small-plaque parapsoriasis exhibit a non-specific spongiotic dermatitis and parakeratosis. Lesions of large-plaque parapsoriasis also may demonstrate an interface lymphocytic infiltrate with lichenoid features. However, when atypical lymphoid cells are present, these specimens are indistinguishable from patch-stage mycosis fungoides .
It is imperative for dermatologists to recognize digitate dermatosis clinically and understand its benign nature and lack of association with mycosis fungoides. This knowledge will decrease anxiety for the patient and physician. As opposed to large-plaque parapsoriasis, in which certain cases will meet criteria for mycosis fungoides and can be treated as such, small-plaque parapsoriasis patients can be followed without treatment or be treated for symptoms or cosmesis. The mainstays of treatment include topical glucocorticoids, topical coal tar products, and ultraviolet B phototherapy .
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