Dermatology MCQ - Inflammatory Dermatoses - Pyodermatitis–pyostomatitis vegetans

A 35-year-old man with a known history of ulcerative colitis presents with painful, verrucous, and vegetative plaques with pustules and erosions in his axillae and groin. The oral mucosa reveals multiple, small, pustules on an erythematous base, which have ruptured to form "snail-track" erosions. A biopsy of a skin lesion would most likely show:

A. Non-caseating granulomas
B. Acantholysis with suprabasal blisters
C. Intraepidermal microabscesses with abundant eosinophils
D. Leukocytoclastic vasculitis with fibrinoid necrosis
E. Dermal mucin deposition with a lichenoid infiltrate

Correct Answer: C. Intraepidermal microabscesses with abundant eosinophils

Answer & Explanation

Explanation:

This presentation is pathognomonic for Pyodermatitis–Pyostomatitis Vegetans (PD-PSV). The combination of vegetative plaques in intertriginous areas and the characteristic oral lesions ("snail-track" ulcers) in a patient with inflammatory bowel disease is diagnostic.

• Key Histopathologic Findings:

  • Intraepidermal microabscesses: The primary finding is the presence of abscesses within the epidermis.

  • Abundant Eosinophils: A very distinctive feature is that these microabscesses are composed predominantly of eosinophils, although neutrophils are also present. This eosinophilic predominance is a key clue.

  • Pseudoepitheliomatous Hyperplasia: The epidermis shows marked hyperplasia, accounting for the verrucous, vegetative clinical appearance.

The other options are histologic findings for other conditions:

• A. Non-caseating granulomas: This is the hallmark of sarcoidosis and Crohn's disease (which can be associated with PD-PSV, but ulcerative colitis is more classic). The skin lesions of Crohn's are typically granulomatous, not pustular and vegetative.

• B. Acantholysis with suprabasal blisters: This is the hallmark of pemphigus vulgaris. While pemphigus can cause oral erosions, it does not cause the vegetative plaques or have the same strong association with IBD.

• D. Leukocytoclastic vasculitis with fibrinoid necrosis: This defines leukocytoclastic vasculitis, which is not a feature of PD-PSV.

• E. Dermal mucin deposition with a lichenoid infiltrate: This is characteristic of lupus erythematosus.

Key Associations for Pyodermatitis–Pyostomatitis Vegetans

• Pathophysiology: PD-PSV is considered a highly specific cutaneous marker for Inflammatory Bowel Disease (IBD), most commonly ulcerative colitis. It is thought to be an immune-mediated reaction to the colonic inflammation. The activity of the skin and oral disease often parallels the activity of the bowel disease.

• Clinical Presentation:

  • Skin (Pyodermatitis Vegetans): Verrucous, boggy, vegetative plaques studded with pustules and erosions, typically in intertriginous areas (axillae, groin, scalp).

  • Oral (Pyostomatitis Vegetans): Multiple small pustules on an erythematous base, which rupture to form characteristic serpiginous, "snail-track" erosions. This is a pathognomonic finding.

• Differential Diagnosis: Includes pemphigus vegetans (a variant of pemphigus vulgaris), blastomycosis, and other deep fungal infections. The history of IBD and the specific histopathology are key to the diagnosis.

• Histopathology: As described above: eosinophilic microabscesses within the epidermis and pseudoepitheliomatous hyperplasia.

• Prognosis: The course is chronic and follows the activity of the underlying IBD. Treatment of the bowel disease often leads to improvement of the skin and oral lesions.

• Management:

  1. Treat the Underlying IBD: This is the cornerstone of management. Control of the colitis with medications (e.g., sulfasalazine, mesalamine, corticosteroids, biologics) or even colectomy often results in resolution of PD-PSV.

  2. Topical Therapies: High-potency topical corticosteroids or topical calcineurin inhibitors (tacrolimus) can be used for localized skin or oral disease.

  3. Systemic Therapies: For severe or refractory cases, systemic corticosteroids, dapsone, or other immunosuppressants may be necessary.