Published on 19/03/2015 by admin
Filed under Dermatology
Last modified 19/03/2015
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Alex Milligan, Rosie Davis and Graham A. Johnston
Evidence Levels: A Double-blind study B Clinical trial ≥ 20 subjects C Clinical trial < 20 subjects D Series ≥ 5 subjects E Anecdotal case reports
The diagnosis parapsoriasis, even as an umbrella term, continues to cause diagnostic difficulties and there is still debate as to whether the variants described in this chapter are in fact precursors of cutaneous T-cell lymphoma. This chapter covers the entities small plaque parapsoriasis (SPP: chronic superficial scaly dermatitis; persistent superficial dermatitis; digitate dermatosis; xanthoerythroderma perstans) and large plaque parapsoriasis (LPP: parakeratosis variegata; retiform parapsoriasis; atrophic parapsoriasis; poikilodermatous parapsoriasis). Confusingly, the term parapsoriasis en plaque has been used for either SPP or LPP.
Other conditions sometimes grouped under the banner of parapsoriasis are pityriasis lichenoides et varioliformis acuta, pityriasis lichenoides chronica, and lymphomatoid papulosis, all of which are the subjects of separate chapters.
The diagnosis of parapsoriasis is made on clinical grounds, with histology supporting the clinical impression, especially when early cutaneous T-cell lymphoma is in the differential diagnosis. Patches of LPP are larger than 5 cm in diameter, and often 10 cm or larger, distinguishing them from SPP, which is characterized by lesions smaller than 5 cm.
If malignancy is considered in the differential diagnosis, T-cell receptor gene rearrangement studies are more likely to demonstrate monoclonality in cutaneous T-cell lymphoma, though monoclonality is not entirely sensitive or specific for the latter. Repeat studies may be warranted if progression to cutaneous T-cell lymphoma is suspected.
Although some advocate non-aggressive therapies, e.g., topical corticosteroids, for parapsoriasis, the potential for progression to cutaneous lymphoma in patients with LPP justifies the use of psoralen with UVA (PUVA). Sunlight, broadband UVB, and narrowband UVB have been used successfully as well, particularly for SPP.
The diagnosis is principally made on clinical findings
Histology is non-specific
TCR gene rearrangement studies
Immunohistochemistry cannot differentiate between the two forms.
Assessment of TCR-beta clonality in a diverse group of cutaneous T-cell infiltrates.
Plaza JA, Morrison C, Magro CM. J Cutan Pathol 2008; 35: 358–65.
Monoclonality is a reliable characteristic of CTCL, polyclonality being very infrequent. However, the authors warn that the various cutaneous lymphoid dyscrasias, including pityriasis lichenoides chronica, could manifest restricted molecular profiles in the context of an oligoclonal process or frank monoclonality.
Clonal T cell receptor gamma-chain gene rearrangement by PCR-based GeneScan analysis in the skin and blood of patients with parapsoriasis and early-stage mycosis fungoides.
Klemke CD, Dippel E, Dembinski A, Pönitz N, Assaf C, Hummel M, et al. J Pathol 2002; 197: 348–54.
Although studies have shown T-cell clonality in both skin and peripheral blood, monoclonality is neither easily demonstrable nor thought to be a prerequisite for diagnosis.
The role of immunohistochemical analysis in the diagnosis of parapsoriasis.
Bordignon M, Belloni-Fortina A, Pigozzi B, Saponeri A, Alaibac M. Acta Histochem 2011; 113: 92–5.
Immunohistochemical techniques cannot distinguish between large and small cell parapsoriasis.
SPP consists of fixed, small scaly erythematous plaques which are asymptomatic or only mildly itchy and occur mainly on the trunk. The lesions sometimes appear to run in finger-like lines parallel to the ribs (hence the name ‘digitate dermatosis’). SPP runs a chronic, indolent, and benign course.
Treatment of Skin Disease Comprehensive Therapeutic Strategies 4e
Emollients, tar, topical corticosteroids
PUVA
Narrowband UVB
