Dermatology MCQ - Viral infections - Pruritic and Dyskeratotic Dermatoses PDD

A 65-year-old woman with a history of chronic lymphocytic leukemia (CLL) presents with a 6-month history of severe, refractory pruritus and widespread, scaly, erythematous papules and plaques with excoriations and lichenification. Some lesions show fine scaling and focal dyskeratosis. She has failed topical corticosteroids and antihistamines. A skin biopsy reveals hyperkeratosis, acanthosis, and dyskeratotic keratinocytes with a perivascular lymphocytic infiltrate. Human polyomavirus 6 (HPyV6) DNA is detected in the lesions via PCR. Which of the following is the most likely diagnosis?

A) Atopic dermatitis
B) Cutaneous T-cell lymphoma (mycosis fungoides)
C) Human polyomavirus-6-associated pruritic and dyskeratotic dermatosis (PDD)
D) Psoriasis
E) Scabies

Correct Answer: C) Human polyomavirus-6-associated pruritic and dyskeratotic dermatosis (PDD)

Explanation

This presentation is characteristic of pruritic and dyskeratotic dermatosis (PDD) associated with human polyomaviruses 6 and 7 (HPyV6/7), a recently described entity in immunocompromised patients.

Key Clinical Features of HPyV6/7-Associated PDD:

• Population: Typically immunocompromised adults (e.g., with CLL, organ transplant recipients, or HIV/AIDS).

• Symptoms: Severe, intractable pruritus resistant to conventional therapies (topical steroids, antihistamines).

• Skin Findings: Widespread, scaly, erythematous papules and plaques with excoriations, lichenification, and fine scaling. May resemble chronic eczema or psoriasis.

• Chronicity: Persists for months to years without spontaneous resolution.

Histopathology:

• Hyperkeratosis, acanthosis, and focal dyskeratosis (individual keratinocyte cell death).

• Perivascular lymphocytic infiltrate in the dermis (often T-cells).

• Lack of specific features of other conditions (e.g., no Pautrier microabscesses for mycosis fungoides, no neutrophils for psoriasis).

Virologic Association:

• HPyV6 or HPyV7 DNA is detected in skin lesions via PCR or in situ hybridization.

• Pathogenesis: The exact role of the virus is unclear, but it is hypothesized that viral replication in keratinocytes triggers dyskeratosis and inflammation, leading to pruritus. Immune dysfunction prevents viral clearance.

Why Not the Other Options?

• (A) Atopic dermatitis: Usually begins in childhood with flexural distribution and responds to topical steroids. Lacks viral association and is less common in older adults without history.

• (B) Cutaneous T-cell lymphoma (mycosis fungoides): Can cause pruritic plaques but shows epidermotropism with atypical lymphocytes (Pautrier microabscesses) on biopsy. IHC is positive for CD3/CD4 with loss of CD7.

• (D) Psoriasis: Features well-demarcated plaques with silvery scale, and biopsy shows neutrophilic microabscesses (Munro microabscesses) and regular acanthosis. Not typically associated with polyomaviruses.

• (E) Scabies: Causes burrows and intense nocturnal pruritus, often with interdigital involvement. Skin scraping reveals mites or eggs. Not associated with dyskeratosis or polyomaviruses.

Management:

• Reduce immunosuppression if possible (e.g., manage CLL).

• Topical or oral antivirals (e.g., cidofovir, valganciclovir) have been attempted with variable success.

• Phototherapy (NB-UVB) may alleviate symptoms.

• Pruritus control: Gabapentin, pregabalin, or dupilumab in refractory cases.

Prognosis:
Chronic and recalcitrant. Improvement may occur with immune restoration or antiviral therapy.

Note: HPyV6/7-associated PDD is a emerging entity, and awareness is crucial for diagnosis in immunocompromised patients with unexplained pruritic eruptions.