Large plaque parapsoriasis

This code describes a rare, chronic inflammatory skin condition characterized by well-demarcated, erythematous, scaly patches or plaques larger than 5 cm. It is considered a low-grade cutaneous T-cell lymphoma (CTCL) and has the potential for progression to mycosis fungoides. Histologically, it involves an atypical lymphoid infiltrate in the upper dermis and epidermis.

Use this code for documented cases of large plaque parapsoriasis, often diagnosed via skin biopsy demonstrating characteristic histopathological features. This diagnosis is typically made by a dermatologist and may involve long-term follow-up due to its malignant potential. Documentation should clearly specify "large plaque" to differentiate it from other parapsoriasis variants.

• Differentiate from small plaque parapsoriasis, which has a benign course and does not progress to CTCL.
• Ensure documentation specifies the "large plaque" variant to support this specific code.
• Consider co-reporting codes for any associated symptoms or complications, such as pruritus (L29.x).