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Parapsoriasis
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 use of the description parapsoriasis or parapsoriasis en plaque , even as an umbrella term, remains controversial, and debate remains whether the variants described in this chapter are, in fact, precursors of cutaneous T-cell lymphoma (CTCL). This chapter covers small plaque parapsoriasis (SPP), which includes the synonyms chronic superficial scaly dermatitis, persistent superficial dermatitis, digitate dermatosis, xanthoerythroderma perstans and hypopigmented parapsoriasis en plaque, and large plaque parapsoriasis (LPP), which includes the synonyms parakeratosis variegata, retiform parapsoriasis, atrophic parapsoriasis, and poikilodermatous parapsoriasis.
Parapsoriasis is often grouped with other cutaneous lymphocytic disorders (including pityriasis lichenoides et varioliformis acuta and pityriasis lichenoides chronica) and cutaneous lymphomas (including lymphomatoid papulosis and mycosis fungoides), all of which are the subjects of separate chapters.
Management Strategy
Although the diagnosis of parapsoriasis is initially considered on clinical grounds, histopathologic examination, including immunohistochemical staining, is essential to exclude CTCL (i.e., early-stage mycosis fungoides or lymphomatoid papulosis). Sometimes T-cell receptor gene rearrangement might help to differentiate between parapsoriasis and CTCL. Monoclonality has been identified in SPP and (more often) in LPP. The presence of a T-cell clone does not appear to predict the risk of progression to CTCL. Regular repeat skin biopsies are recommended if a clinical or histologic progression to CTCL is suspected.
Although topical therapy is appropriate in mild or early cases, the potential for progression to cutaneous lymphoma in patients with parapsoriasis can justify the use of phototherapy in symptomatic or advanced cases.
Furthermore, recent studies suggest an increased risk for vascular events, including venous thromboembolism, stroke, and acute myocardial infarction. Therefore, risk assessment for vascular events is recommended.
Specific Investigations
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Hypopigmented parapsoriasis en plaque, a new, overlooked member of the parapsoriasis family: a report of 34 patients and a 7-year experience
El Darouti MA, Fawzy MM, Hegazy RA, et al. J Am Acad Dermatol 2012; 67: 1182–8.
The authors describe a new variant of hypopigmented parapsoriasis that phenotypically showed most features of SPP. Immunohistochemically, the T-cell infiltrate was mostly CD8+, in contrast to the regular parapsoriasis with a CD4+ infiltrate in most cases; 14% developed a hypopigmented mycosis fungoides.
Skin microbiome in small- and large-plaque parapsoriasis
Salava A, Pereira P, Aho V, et al. Acta Derm Venereol 2017; 97: 685–91.
The study described the microbiome in patients with SPP and LPP. No difference in microbiome was observed between the lesional skin microbiome and contralateral healthy skin microbiome. No difference in SPP and LPP could be made although interpersonal variation was demonstrated. Overall, the results suggest that parapsoriasis is not associated with significant alterations in the cutaneous bacterial microbiome.
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, et al. J Pathol 2002; 197: 348–54.
Although the authors of this paper concede that studies have shown T-cell clonality in both skin and peripheral blood, they argue that monoclonality is neither easily demonstrable nor a prerequisite for diagnosis.
The role of immunohistochemical analysis in the diagnosis of parapsoriasis
Bordignon M, Belloni-Fortina A, Pigozzi B, et al. Acta Histochem 2011; 113: 92–5.
Given the lack of clinical and histologic markers of distinction between parapsoriasis and early CTCL, the use of immunohistochemical techniques has been explored to try to establish a more definitive diagnosis. However, these techniques, including CD4/CD8 ratio, expression of T-cell antigens, and expression of proliferation markers, have been found unhelpful in distinguishing between parapsoriasis and early CTCL.
Small Plaque Parapsoriasis
SPP consists of fixed, scaly erythematous plaques less than 5 cm in diameter. They are predominantly asymptomatic but can be mildly pruritic and occur mainly on the trunk and proximal extremities. The lesions sometimes appear to run in fingerlike lines parallel to the ribs (hence the synonym digitate dermatosis). The histology is only supportive for SPP and shows mild acanthosis with focal parakeratosis and small areas of perivascular lymphocytic infiltrate within the papillary dermis. Single cell epidermotropism can be present. Nevertheless, Pautrier microabscesses, a prominent feature of mycosis fungoides, are usually absent. SPP runs a chronic, indolent, and usually benign course.
First-Line Therapies
Treatments with emollients, topical tar, and topical corticosteroid are widely used, but evidence is anecdotal, and these treatments are therefore unreferenced.
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