BASICS
DESCRIPTION
- Parapsoriasis describes a group of cutaneous diseases characterized by scaly patches or plaques that resemble psoriasis.
- There are three main types of parapsoriasis:
- Pityriasis lichenoides
- Small plaque parapsoriasis (see separate chapter)
- Large plaque parapsoriasis (LPP)
- LPP is a cutaneous disease of scaly patches and plaques caused by a T-cell lymphoproliferative disorder, which may precede cutaneous T-cell lymphoma (CTCL). The superficial dermal infiltrate is composed primarily of CD4+ T cells often with a dominant T-cell type (clonality).
- It is characterized by psoriasiform epidermal hyperplasia and areas of poikiloderma (a combination of mottled pigmentation, telangiectasia, and epidermal atrophy).
- Histology shows vacuolization in the basal keratinocyte layer, capillary dilation, and a lymphocytic infiltrate with a bandlike distribution along the dermoepidermal junction.
- Plaques may become secondarily infected (impetiginized) secondary to scratching and excoriation.
EPIDEMIOLOGY
Incidence
There are no good data reflecting the true incidence of LPP.
ETIOLOGY AND PATHOPHYSIOLOGY
- LPP is a chronic inflammatory disorder likely caused by long-term stimulation of a specific subset of T cells by a corresponding antigen. This causes particular T cells to proliferate, resulting in a dominant T-cell clone that may represent up to 50% of the T-cell infiltrate. If atypical lymphocytes are present, classification as patch stage CTCL may be warranted.
- 10% of LPP cases per year progress to CTCL, and some believe LPP is actually the earliest stage of CTCL.
- Human herpesvirus type 8 has been detected in >85% of LPP lesions.
- Several theories have been postulated regarding etiology, but all studies have been inconclusive.
RISK FACTORS
Specific risk factors have not been identified.
GENERAL PREVENTION
There are no known preventative measures.
COMMONLY ASSOCIATED CONDITIONS
10% of LPP patients per year will progress to mycosis fungoides (MF), a type of CTCL.
DIAGNOSIS
- LPP is a chronic condition that develops progressively from a few patches into more visible ones over decades.
- LPP, as opposed to small plaque parapsoriasis, does not enter remission without treatment and may progress to MF, a CTCL.
- Retiform parapsoriasis is a rare variant of LPP with widespread, ill-defined patches in a net-like or zebra-stripe pattern. It almost always progresses to MF.
PHYSICAL EXAM
- Patches and plaques are >6 cm and irregularly shaped with smooth, round borders. They often show epidermal atrophy or poikiloderma.
- Plaques are smooth with a fine scale, faint red-brown color, and tissue paper " like wrinkling quality. They are either asymptomatic or mildly pruritic.
- Plaques occur primarily on the buttocks, lower extremities, lower trunk, and non " sun-exposed areas, and may disappear after exposure to ultraviolet (UV) light.
- In disease that progresses to CTCL, there is an average of 6.1 years between onset of parapsoriasis and the microscopic diagnosis of CTCL.
DIFFERENTIAL DIAGNOSIS
- Psoriasis
- Pityriasis rosea
- Pityriasis alba
- Nummular dermatitis
- CTCL
- Contact dermatitis, allergic
- Secondary syphilis
DIAGNOSTIC TESTS & INTERPRETATION
- Perform skin biopsy. LPP is characterized by a lymphocytic infiltrate in the dermoepidermal junction, dilated blood vessels, melanophages, flattening of rete ridges, irregular hyperkeratosis, and spotty parakeratosis of the cornified layer.
- If diagnosis of LPP is suggested, perform CBC with differential. The presence of Sezary cells suggests CTCL.
- Perform immunophenotyping analysis and gene rearrangement studies to identify atypical T cells (1).
TREATMENT
Treatment may prevent progression to CTCL.
MEDICATION
First Line
- Mid- to high-potency topical steroid cream applied 1 to 2 times daily (classes II to IV)
- Topical tar products
- Phototherapy with broad or narrow-band UVB rays, or UVA therapy with or without psoralens (2). Occasionally, natural UV light may be substituted.
Second Line
- Topical nitrogen mustard (mechlorethamine) and topical carmustine (BCNU) for the poikilodermatous type. (These may cause contact dermatitis.)
- Targretin gel
- Topical bexarotene
- Topical imiquimod
ISSUES FOR REFERRAL
Refer LPP patients to a dermatologist due to complex treatment options and potential progression to CTCL.
ONGOING CARE
Follow up every 3 to 6 months. Increasing number of lesions, increase in lesion size, or the development of induration or epidermal atrophy should prompt a repeat skin biopsy.
PROGNOSIS
- LPP can persist for years to decades with little change but 10% per year progress to CTCL.
- The 5-year survival rate is >90%.
- The retiform variant progresses to CTCL in all cases.
REFERENCES
11 Bordignon M, Belloni-Fortina A, Pigozzi B, et al. The role of immunohistochemical analysis in the diagnosis of parapsoriasis. Acta Histochem. 2011;113(2):92 " 95.22 Duarte IA, Korkes KL, Amorim VA, et al. An evaluation of the treatment of parapsoriasis with phototherapy. An Bras Dermatol. 2013;88(2):306 " 308.
ADDITIONAL READING
- Kreuter A, Bischoff S, Skrygan M, et al. High association of human herpesvirus 8 in large-plaque parapsoriasis and mycosis fungoides. Arch Dermatolo. 2008;144(8):1011 " 1016.
- Lindahl, Fenger-Gr Έn M, Iversen L. Subsequent cancers, mortality, and causes of death in patients with mycosis fungoides and parapsoriasis: a Danish nationwide, population-based cohort study. J Am Acad Dermatol 2014;71(3):529 " 535.
- Sarveswari KN, Yesudian P. The conundrum of parapsoriasis versus patch stage of mycosis fungoides. Indian J Dermatol Venereol Leprol. 2009;75(3):229 " 235.
CODES
ICD10
L41.4 Large plaque parapsoriasis
ICD9
696.2 Parapsoriasis
SNOMED
Large plaque parapsoriasis (disorder)
CLINICAL PEARLS
- LPP presents as irregularly shaped scaly plaques >6 cm in diameter with smooth, round borders and epidermal atrophy.
- Look for the "bathing suit " distribution of plaques.
- LPP develops steadily over weeks to months and can last for decades with a 10% chance per year of progression to CTCL.