What Is Parapsoriasis?
Parapsoriasis is a rare group of inflammatory skin conditions characterized by scaly patches or plaques resembling psoriasis but differing in appearance and behavior. It primarily affects middle-aged adults, with a male predominance.
What Are the Types of Parapsoriasis?
1. Small Plaque Parapsoriasis (SPP)
- Appearance: Small, round or oval patches less than 5 cm in diameter.
- Location: Commonly affects the trunk and limbs.
- Prognosis: Generally benign with a low risk of progression to cutaneous T-cell lymphoma (CTCL).
2. Large Plaque Parapsoriasis (LPP)
- Appearance: Larger, irregularly shaped patches exceeding 5 cm in diameter.
- Location: Typically found on areas with minimal sun exposure, such as the thighs, buttocks, and lower abdomen.
- Prognosis: Considered a premalignant condition with a higher risk of evolving into CTCL, particularly mycosis fungoides.
What Causes Parapsoriasis?
The exact cause remains unknown. However, it is believed to result from a combination of genetic predisposition and environmental factors, leading to abnormal T-cell activity in the skin.
How Is Parapsoriasis Diagnosed?
- Clinical Evaluation: Assessment of skin lesions’ appearance and distribution.
- Skin Biopsy: Microscopic examination to differentiate from other conditions like CTCL.
- Additional Tests: In some cases, T-cell receptor gene rearrangement studies may be conducted to assess the risk of malignancy.
What Are the Treatment Options?
For Small Plaque Parapsoriasis:
- Topical Treatments: Emollients, mid-potency corticosteroids, or tar preparations.
- Phototherapy: Narrowband UVB or PUVA therapy may be considered for resistant cases.
For Large Plaque Parapsoriasis:
- Topical Treatments: High-potency corticosteroids, topical nitrogen mustard, or carmustine.
- Phototherapy: Narrowband UVB or PUVA therapy is commonly used.
- Monitoring: Regular follow-up is essential to detect any progression to CTCL.
What Is the Prognosis?
- Small Plaque Parapsoriasis: Typically remains stable without progression to malignancy.
- Large Plaque Parapsoriasis: Approximately 10% of individuals may develop CTCL over a decade.