BASICS
DESCRIPTION
- Parapsoriasis describes a group of cutaneous diseases characterized by scaly patches or slightly raised plaques that resemble psoriasis.
- There are three main types of parapsoriasis:
- Pityriasis lichenoides
- Large plaque parapsoriasis (see separate chapter)
- Small plaque parapsoriasis (SPP)
- SPP is a rare, commonly benign chronic dermatitis most often seen in middle-aged men.
- SPP presents as well-circumscribed, round/oval, erythematous/salmon-colored, scaly patches or plaques 1 to 5 cm in length and scattered over the trunk and extremities (sun-protected areas). It is generally asymptomatic or mildly pruritic.
- Patches exhibit parakeratosis and a sparse perivascular cutaneous lymphoid infiltrate primarily composed of CD4+ T cells.
- Digitate dermatosis is a variant of SPP that consists of elongated, fingerlike patches that are symmetrically distributed along dermatomes of the flanks and may exceed 5 cm in length. This form may be underreported because of lack of symptoms and subtle presentation.
- A hypopigmented variant of SPP, characterized by a CD8+ predominant T-cell infiltrate, may be seen especially in darker skinned individuals (1).
- SPP may persist, resolve spontaneously (sometimes after several years), or rarely may progress to mycosis fungoides (MF), the most common form of primary cutaneous T-cell lymphoma (CTCL) (2). Digitate dermatosis does not progress to MF.
EPIDEMIOLOGY
Incidence
SPP most often presents in middle-aged men in the 5th decade of life, with a 3:1 ratio of men to women.
ETIOLOGY AND PATHOPHYSIOLOGY
SPP is likely a reactive process in which a specific subset of T cells multiplies in response to a corresponding antigen. This can produce an excess of one type of T cell or monoclonality of the lymphocytic infiltrate. Specific exposures or antigens have not been identified, although a viral etiology is suspected.
RISK FACTORS
Specific risk factors have not been identified.
GENERAL PREVENTION
No known preventative measures
COMMONLY ASSOCIATED CONDITIONS
CTCL, most often MF
DIAGNOSIS
HISTORY
Onset of SPP is indolent, developing from a few patches and becoming more visible over an extended period of time. It can last months to several years and often resolves spontaneously. SPP often responds to steroid creams or phototherapy treatment but may relapse. Small plaques may grow in size and number as disease progresses.
PHYSICAL EXAM
- Oval/round plaques 1 to 5 cm in diameter on the limbs and upper trunk
- Light red color, with fine scale and slightly wrinkled surface
- Some plaques have a yellowish hue, which is termed xanthoerythrodermia perstans.
- Digitate dermatosis variant presents symmetrically over the trunk as elongated fingerlike plaques up to 10 cm in length.
DIFFERENTIAL DIAGNOSIS
- CTCL
- Nummular dermatitis
- Psoriasis
- Pityriasis rosea
- Pityriasis lichenoides chronica
- Secondary syphilis
DIAGNOSTIC TESTS & INTERPRETATION
- Perform skin biopsy. SPP is characterized by perivascular dermal infiltrates of lymphocytes with exocytosis in the epidermis, epidermal atrophy, edema, and focal hyperkeratosis.
- If diagnosis of SPP is suggested, perform CBC with differential to screen for Sezary cells (seen in CTCL).
- Perform immunophenotyping analysis and gene rearrangement studies to identify atypical T cells.
TREATMENT
- Typically managed conservatively, often with minimal or no treatment necessary
- Topical treatment is effective.
First Line
- Emollients
- Moderate to high potency topical corticosteroid cream applied 1 to 2 times per day
- For widely scattered lesions, use phototherapy with broad or narrow-band UVB rays or UVA therapy with or without psoralens. Occasionally, natural UV light may be substituted.
Second Line
- Nitrogen mustard (3)
- Topical tacrolimus
- Coal tar products
- Bexarotene
- Bicalutamide (Casodex) for variant digitate dermatosis
ONGOING CARE
PATIENT MONITORING
- Annual follow-up is recommended.
- If epidermal atrophy occurs, consider a repeat skin biopsy.
PATIENT EDUCATION
- Patients should watch for an increase in the number/size of lesions in addition to the development of induration/epidermal atrophy.
- Reassure patients of the benign self-limiting nature of the disease.
PROGNOSIS
A small number of SPP cases may progress to MF even after treatment. In one study of 69 subjects, after 10 years, 51% were healed, 36% had active SPP, and 10% had developed MF.
REFERENCES
11 El-Darouti MA, Fawzy MM, Hegazy RA, et al. Hypopigmented parapsoriasis en plaque, a new, overlooked member of the parapsoriasis family: a report of 34 patients and a 7-year experience. J Am Acad Dermatol. 2012;67(6):1182 " 1188.22 V €kev € L, Sarna S, Vaalasti A, et al. A retrospective study of the probability of the evolution of parapsoriasis en plaques into mycosis fungoides. Acta Derm Venereol. 2005;85(4):318 " 323.33 Lindahl LM, Fenger-Gron M, Iversen L. Topical nitrogen mustard therapy in patients with mycosis fungoides or parapsoriasis. J Eur Acad Dermatol Venereol. 2013;27(2):163 " 168.
ADDITIONAL READING
- Bolognia J, Jorizzo JL, Rapini RP. Dermatology. 2nd ed. St. Louis, MO: Mosby Elsevier; 2008.
- Sehgal VN, Srivastava G, Aggarwal A. Parapsoriasis: a complex issue. Skinmed. 2007;6(6):280 " 286.
- Zeybek ND, Asan E, Erbil AH, et al. Immunohistochemical analysis of small plaque parapsoriasis: involvement of dendritic cells. Acta Histochem. 2008;11(5):380 " 387.
CODES
ICD10
L41.3 Small plaque parapsoriasis
ICD9
696.2 Parapsoriasis
SNOMED
Small plaque parapsoriasis
CLINICAL PEARLS
- SPP presents as well-demarcated round/oval minimally scaly plaques <5 cm in diameter.
- The World Health Organization considers SPP a benign disease with little to no potential for transformation into lymphoma.
- Digitate dermatosis is a variant of SPP that presents as elongated fingerlike projections up to 10 cm in length and never progresses to MF.