Parapsoriasis is a rare cutaneous lymphoproliferative dermatosis that primarily affects middle-aged adults, with a higher incidence in males. Due to its diverse clinical presentation and lack of specific histopathological findings, defining and diagnosing this disorder can be challenging. In this article, we will explore the types of parapsoriasis, its clinical manifestations, and available treatment options. We will also discuss the potential risk of progression to mycosis fungoides or cutaneous T-cell lymphoma associated with large plaque parapsoriasis.
Types of Parapsoriasis:
There are two main types of parapsoriasis: small plaque parapsoriasis (SPP) and large plaque parapsoriasis (LPP). SPP is considered a chronic benign condition, while LPP is regarded as a premalignant dermatosis with a risk of transforming into mycosis fungoides or cutaneous T-cell lymphoma. The lesions in SPP are typically pink to yellow-brown, round or oval macules or patches ranging in size from 2 to 5cm. In contrast, LPP presents as large irregularly shaped dusky red or brown patches with fine scales. The clinical characteristics help differentiate between these two types and guide treatment decisions.
Clinical Presentation and Diagnosis:
SPP lesions are often asymptomatic and mainly appear on the trunk, flanks, and proximal extremities. The microscopic examination of SPP biopsies shows nonspecific findings such as mild spongiosis, parakeratosis, scale, and exocytosis of small lymphocytes. A variant of SPP, known as digitate dermatosis, features elongated patches with an atrophic cigarette paper-like surface along the skin cleavage lines. On the other hand, LPP lesions exhibit epidermal atrophy and are commonly found in non-sun-exposed areas such as the buttocks, thighs, lower trunk, flexural surfaces, breasts, and inframammary areas. Microscopic examination of LPP biopsies reveals psoriasiform epidermal hyperplasia, poiklodermatous areas, vacuolization in the basal layer, and brisk lymphocytic infiltration. The absence of Pautrier microabscesses, clusters of atypical lymphocytes, helps distinguish LPP from mycosis fungoides.
Diagnosis and Monitoring:
A definitive diagnosis of parapsoriasis requires a proper clinical presentation as described above and a skin biopsy. Punch biopsy is commonly performed to obtain a full-thickness skin sample, and multiple biopsies from different areas may be necessary due to the diverse morphology. It is also recommended to perform biopsies over time to monitor disease progression, particularly in cases of LPP. Regular follow-up visits are essential, with SPP patients typically requiring annual check-ups and LPP patients being monitored every six months due to the potential risk of malignancy.
The treatment approach for SPP starts with the use of moderate to high potency topical corticosteroids for 8-12 weeks. If the response is inadequate (less than 50% clearance), phototherapy may be added 2-3 times a week. Similarly, topical corticosteroids are the initial treatment for LPP, using high or super high potency formulations for approximately 12 weeks. In cases of extensive skin involvement, phototherapy is often initiated alongside topical treatment, with sessions scheduled 2-3 times a week.
Parapsoriasis is a rare dermatological condition with distinct clinical presentations and potential risks associated with disease progression. Differentiating between small plaque parapsoriasis and large plaque parapsoriasis is crucial, as the latter has a premalignant nature. Accurate diagnosis through clinical evaluation and skin biopsy allows for appropriate treatment selection and monitoring of disease progression. By utilizing topical corticosteroids and phototherapy, healthcare professionals aim to manage symptoms and reduce the risk of complications in patients with parapsoriasis.
 American Osteopathic College of Dermatology. “Parapsoriasis.” Retrieved from https://www.aocd.org/page/Parapsoriasis