Large plaque parapsoriasis

Large plaque parapsoriasis (LPP) is a rare skin disorder that falls within the spectrum of cutaneous T-cell lymphoma (CTCL), specifically the parapsoriasis group. It is characterized by the presence of large, scaly, well-demarcated plaques, predominantly affecting the trunk and limbs. The condition is chronic and has a potential for transformation into more aggressive forms of lymphoma, such as Mycosis fungoides.

Etiology

The exact cause of large plaque parapsoriasis remains unknown. However, it is believed to involve a combination of genetic predisposition and environmental factors. Abnormalities in the immune system, particularly involving T-cells, play a central role in its pathogenesis.

Clinical Features

Patients with large plaque parapsoriasis typically present with large, round or oval, erythematous plaques. These lesions often have a fine scale and are usually located on the trunk, buttocks, and proximal extremities. Unlike small plaque parapsoriasis, LPP lesions are larger than 5 cm in diameter and tend to be more persistent and symptomatic. Pruritus (itching) can be a significant symptom, affecting the quality of life of the patients.

Diagnosis

The diagnosis of large plaque parapsoriasis is primarily clinical, supported by histopathological findings from skin biopsies. Histology typically shows a superficial perivascular lymphocytic infiltrate with epidermotropism but without the formation of Pautrier microabscesses, which are characteristic of mycosis fungoides. Immunohistochemistry may reveal an atypical CD4+ T-cell population. Additional tests, including T-cell receptor gene rearrangement studies, can help in differentiating LPP from other forms of CTCL.

Treatment

Treatment of large plaque parapsoriasis aims to control symptoms and prevent progression to more aggressive lymphomas. Options include topical corticosteroids, phototherapy (particularly narrowband UVB and PUVA), and systemic agents in more severe cases. Regular follow-up is essential to monitor for signs of transformation to mycosis fungoides or other lymphomas.

Prognosis

The prognosis of large plaque parapsoriasis is variable. While the condition itself is not life-threatening, there is a recognized risk of transformation into mycosis fungoides, which carries a worse prognosis. Early detection and treatment of such transformations are crucial for improving outcomes.

Epidemiology

Large plaque parapsoriasis is a rare condition, with a higher prevalence in males and typically presenting in middle-aged to elderly individuals. The exact incidence and prevalence rates are unknown due to its rarity and the overlap with other forms of CTCL.

See Also

• Cutaneous T-cell lymphoma
• Mycosis fungoides
• Parapsoriasis
• Phototherapy

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