eMedicine Specialties > Dermatology > Papulosquamous Diseases

Parapsoriasis

Author: Henry K Wong, MD, PhD, Senior Professional Staff, Department of Dermatology, Henry Ford Hospital
Contributor Information and Disclosures

Updated: Mar 13, 2009

Introduction

Background

Parapsoriasis describes a group of cutaneous diseases that can be characterized by scaly patches or slightly elevated papules and/or plaques that have a resemblance to psoriasis, hence the nomenclature. However, this description includes several inflammatory cutaneous diseases that are unrelated with respect to pathogenesis, histopathology, and response to treatment. Because of the variation in clinical presentation and a lack of a specific diagnostic finding on histopathology, a uniformly accepted definition of parapsoriasis remains lacking.

In 1902, Brocq initially described 3 major entities that fit the description:

• Pityriasis lichenoides (acuta and chronica)
• Small plaque parapsoriasis
• Large plaque parapsoriasis (parapsoriasis en plaque)

Pityriasis lichenoides (acuta and chronica)

Pityriasis lichenoides variants describe scaly dermatoses with necrotic papules that are clinically and histologically different from parapsoriasis. These diseases generally are benign and undergo spontaneous resolution, but at times may have a protracted course (see Pityriasis Lichenoides for further discussion).

Large plaque and small plaque parapsoriasis

Current terminology of parapsoriasis refers to 2 disease processes that are caused by T-cell–predominant infiltrates in the skin. These disease processes are large plaque parapsoriasis and small plaque parapsoriasis.

As the nomenclature and description of the disease spectrum under the descriptive term parapsoriasis evolved, the primary focus has been on the distinction of whether the disorder progresses to mycosis fungoides (MF) or cutaneous T-cell lymphoma (CTCL). Small plaque parapsoriasis is a benign disorder that rarely if ever progresses. Large plaque parapsoriasis is more ominous in that approximately 10% of patients progress to MF/CTCL.¹ Controversy exists currently in the classification of large plaque parapsoriasis because some believe it is equivalent to the earliest stage CTCL, the patch stage.^2,3,4

The duration of parapsoriasis can be variable. Small plaque disease lasts several months to years and can spontaneously resolve. Large plaque disease is chronic, and treatment is recommended because it may prevent progression to CTCL.

Pathophysiology

The initiating cause of parapsoriasis is unknown, but the diseases likely represent different stages in a continuum of lymphoproliferative disorders from chronic dermatitis to frank malignancy of CTCL.

Small plaque parapsoriasis

Small plaque parapsoriasis likely is a reactive process of predominantly CD4⁺ T cells. Genotypic pattern observed in small plaque parapsoriasis is similar to that observed in chronic dermatitis, and the pattern of clonality of T cells is consistent with the response of a specific subset of T cells that have been stimulated by an antigen. Multiple dominant clones can be detected by polymerase chain reaction (PCR) of T-cell receptor gene usage, which supports a reactive process. Lymphocytes do not show histologic atypia to suggest malignant transformation. Southern blot analysis of T-cell receptor genes from parapsoriasis does not identify a dominant clone of T cells.

Some physicians believe that small plaque parapsoriasis is an abortive T-cell lymphoma; however, no clear distinguishing evidence, such as genetic changes (eg, TP53 mutations) observed in other malignancies, exists to support this contention.⁵ Nevertheless, a hint to the verity of this hypothesis is the recent identification of increased telomerase activity in T cells from CTCL at low-grade stages, high-grade lymphoma, and in parapsoriasis, which is activity not exhibited in normal T cells. A better understanding is likely to develop from further molecular characterization.⁶

Large plaque parapsoriasis

Large plaque parapsoriasis is a chronic inflammatory disorder, and the pathophysiology has been speculated to be long-term antigen stimulation. This disorder is associated with a dominant T-cell clone, one that may represent up to 50% of the T-cell infiltrate. If the histologic appearance is benign, without atypical lymphocytes, classification of large plaque parapsoriasis is made. If atypical lymphocytes are present, many would classify such patients as having patch stage CTCL.

Human herpesvirus type 8 has been detected in up to 87% of skin lesions of large plaque parapsoriasis. This is the first association of a specific infectious agent with large plaque parapsoriasis, and the significance is unclear. Further studies are important to determine the significance of this finding.⁷

Frequency

United States

No accurate statistics on the incidence and frequency of parapsoriasis exist, but digitate dermatoses may be underreported because of the lack of symptoms and subtle presentation.

Patients may underreport the frequency of large plaque parapsoriasis when it is asymptomatic and subtle. Large plaque parapsoriasis may be greater than the reported incidence of MF, which is approximately 3.6 cases per million population per year.

International

No reported racial or geographic predilection exists.

Mortality/Morbidity

• Mortality has not been reported for small plaque parapsoriasis. Morbidity is limited to symptoms, which are minimal.
• For large plaque parapsoriasis, mortality may be associated with progression to MF (CTCL). Patch stage of MF represents the early stages of CTCL, and the 5-year survival rate is greater than 90%. Long-term survival is not different from a matched controlled population.⁸

Race

No association with race is noted.

Sex

Small plaque parapsoriasis is associated with male predominance. The male-to-female ratio is 3:1. A slight asymmetry favoring male dominance for large plaque parapsoriasis may exist.

Age

For both small plaque parapsoriasis and large plaque parapsoriasis, presentation most frequently is in middle age; peak incidence is in the fifth decade of life.

Clinical

History

Onset of parapsoriasis is indolent. It develops from a few patches and becomes more visible over a protracted period of time. Additional lesions develop progressively in some individuals.

• Small plaque parapsoriasis can last months to several years; the disease often resolves spontaneously.
• Large plaque parapsoriasis is a chronic disorder that manifests in an indolent manner and progresses over many years, sometimes decades.
  • Large plaque parapsoriasis does not enter remission without treatment.
  • The disorder may progress to MF, a CTCL, after an indeterminate number of years.

Physical

• Lesions of small plaque parapsoriasis are well-circumscribed, slightly scaly, light salmon-colored patches that measure less than 5 cm in diameter and are scattered over the trunk and extremities. Digitate pattern is a distinctive form of small plaque disease that consists of palisading elongated fingerlike patches that follow the dermatome and are most prominently displayed on the lateral thorax and abdomen.

• Large plaque parapsoriasis manifests as faint erythematous patches with arcuate geographic borders.
  • Each lesion often is greater than 6 cm in diameter.
  • Lesions are scattered on the proximal extremities and the trunk.
  • Lesions often show a bathing suit distribution.
  • Surfaces of the lesions have a faint red-to-salmon color; show flaky thin scales; and have an atrophic, cigarette paper or tissue paper, wrinkling quality.

Causes

No clear etiology for small plaque or large plaque parapsoriasis is known, and no specific association has been made with contact exposure or infections.

• Search for CME/CE on This Topic »

• Cutaneous T-Cell Lymphoma (Dermatology)
• Pseudoatrophoderma Colli (Dermatology)
• Pityriasis Lichenoides (Dermatology)