Parapsoriasis



Parapsoriasis


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


image


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.




Management strategy


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.



Specific investigations






Immunohistochemistry cannot differentiate between the two forms.









Small plaque 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.



First-line therapies















image Emollients, tar, topical corticosteroids E
image PUVA C
image Narrowband UVB C


Treatments with emollients, topical tar, and topical corticosteroid are cited in books, and appear effective in clinical practice. There have, however, been no studies or case reports to back this up, and these treatments are therefore unreferenced.





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Aug 7, 2016 | Posted by in Dermatology | Comments Off on Parapsoriasis

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