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Chapter 8: Parapsoriasis

Manasmon Chairatchaneeboon; Ellen J. Kim

PARAPSORIASIS

Therapeutic Approach

Parapsoriasis is a group of uncommon chronic benign papulosquamous dermatosis, also known as “Parapsoriasis en plaque.” It can be classified as small plaque parapsoriasis (SPP) and large plaque parapsoriasis (LPP) and despite the name, it is not related to psoriasis. Lesions of SPP are round to oval erythematous patches with fine scales, usually less than 5 cm in size. Most of the lesions are located on the trunk and proximal extremities. Digitate dermatosis is a distinct form of SPP, characterized by thin elongated patches arranged in parallel on both flanks, and the long axis may be longer than 5 cm. LPP refers to a subtype of parapsoriasis with skin lesions larger than 5 cm, distributed on the trunk, thighs, buttocks, and over the breasts. Wrinkling skin, poikiloderma, or retiform patches may be apparent in LPP. Clinical, immunohistopathology, and T-cell clonality in some LPP cases may overlap considerably with patch stage mycosis fungoides (MF). Some authors considered LPP as a premycotic dermatosis.1-3 Approximately 10% to 30% of LPP patients may progress to MF, but this event is extremely rare in SPP.4

Most cases of parapsoriasis are asymptomatic or mildly pruritic and may be recalcitrant to treatment. There are no randomized trials for the treatment of this condition, but typically patients are treated initially with mid- or high-potency topical corticosteroids and natural sunlight/heliotherapy, with more extensive or refractory cases treated with narrowband UVB phototherapy or mechlorethamine gel if available. Regarding the risk of progression to MF, the recalcitrant LPP cases should be biopsied periodically and may be treated as MF with variable results. See Table 8-1.

Table 8-1Parapsoriasis Treatment Table
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Table 8-1 Parapsoriasis Treatment Table
MEDICATION NAME INDICATION** MECHANISM OF ACTION DOSING ADVERSE EFFECTS SUGGESTED MONITORING LEVEL OF EVIDENCE (REFERENCE)
Topical Therapy
Steroids (if BSA > 5%, mid-potency such as triamcinolone cream or ointment 0.1% × 2-4 wk, if BSA < 5% high-potency such as clobetasol cream or ointment 0.05% BID if 2-4 wk). Parapsoriasis Anti-inflammatory, antiproliferative Apply QD-BID Skin atrophy, telangiectasia, striae, acneiform reaction, infection, hypertrichosis, systemic absorption None III2,3
Ultraviolet B (UVB) phototherapy—broadband or narrowband Parapsoriasis Immunomodulatory, immunosuppressive, T-cell apoptosis 2-3 times a week Erythema, blistering, pruritus, pigmentation, photoaging, skin cancer None III5-11
PUVA (psoralen plus UVA) phototherapy Parapsoriasis Immunomodulatory, immunosuppressive, T-cell apoptosis 2-3 times a week Erythema, blistering, pruritus, pigmentation, photoaging, skin cancer, nausea (30%), cataracts None III10-12
Bath PUVA Parapsoriasis Immunomodulatory, immunosuppressive, T-cell apoptosis 2-3 times a week Erythema, blistering, pruritus, pigmentation, unknown long-term side effects None IV13
Topical PUVA Parapsoriasis Immunomodulatory, immunosuppressive, T-cell apoptosis 2-3 times a week Bullous phototoxic reaction, irregular pigmentation None IV14
UVA1 phototherapy Parapsoriasis Immunomodulatory, immunosuppressive, T-cell apoptosis 3-5 times a week Erythema, pruritus, marked pigmentation, photoaging, skin cancer None III15-17
Excimer—laser (308 nm) phototherapy Localized parapsoriasis Immunomodulatory, immunosuppressive, T-cell ...

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