Dermatology MCQ - Inflammatory Dermatoses - Pyoderma Gangrenosum

A 55-year-old woman with a history of ulcerative colitis presents with a rapidly enlarging, exquisitely tender ulcer on her left shin. The ulcer has a characteristic violaceous, undermined border and a purulent base. She reports that the lesion started as a small pustule and expanded over a few days following a minor trauma. The most appropriate initial step in management is:

A. Initiate high-dose intravenous broad-spectrum antibiotics.
B. Obtain a tissue biopsy from the ulcer edge for culture and histopathology.
C. Initiate systemic corticosteroid therapy (e.g., prednisone 1 mg/kg/day).
D. Perform surgical debridement to remove necrotic tissue.
E. Initiate high-potency topical corticosteroids under occlusion.

Correct Answer: C. Initiate systemic corticosteroid therapy (e.g., prednisone 1 mg/kg/day).

Answer & Explanation

Explanation:

This presentation is classic for Pyoderma Gangrenosum (PG). The key features are: rapid progression, a violaceous undermined border, association with an underlying systemic disease (ulcerative colitis), and pathergy (lesion induced by minor trauma).

The management of PG is primarily immunosuppression, not antibiotics or surgery.

• Why this is correct: Systemic corticosteroids are the first-line treatment for rapidly progressive or severe PG. They act quickly to suppress the neutrophilic inflammation and halt the progression of the ulcer.

The other options are incorrect or potentially harmful:

• A. Initiate high-dose intravenous broad-spectrum antibiotics: While the ulcer has a purulent base, this is sterile inflammation (neutrophilic infiltrate), not an active infection. Antibiotics are only indicated if there is a secondary bacterial infection, which is not the primary driver of the lesion.

• B. Obtain a tissue biopsy from the ulcer edge for culture and histopathology: A biopsy is often performed and can be supportive, showing a dense neutrophilic infiltrate. However, the diagnosis of PG is primarily clinical. In a case with such classic features, biopsy should not delay the initiation of urgent immunosuppressive therapy. Furthermore, biopsy can worsen the lesion due to pathergy.

• D. Perform surgical debridement to remove necrotic tissue: This is contraindicated in the active phase of PG due to the high risk of pathergy, which would cause the ulcer to enlarge dramatically.

• E. Initiate high-potency topical corticosteroids under occlusion: Topical or intralesional corticosteroids can be used for very early, limited, or superficial PG. For a rapidly enlarging, painful ulcer as described, systemic therapy is required for adequate control.

Key Associations for Pyoderma Gangrenosum

• Pathophysiology: PG is a neutrophilic dermatosis, a disorder of innate immunity. It is not an infectious or primary vasculitic process.

• Associated Conditions (in ~50% of cases):

  • Inflammatory Bowel Disease: (Ulcerative colitis > Crohn's disease).

  • Inflammatory Arthritis: (Rheumatoid arthritis, seronegative arthritis).

  • Hematologic Disorders: (Monoclonal gammopathy of undetermined significance - MGUS, myeloma, leukemia).

  • Autoimmune Disease: (e.g., SLE).

• Pathergy: The development of new lesions or worsening of existing ones at sites of minor skin injury (e.g., biopsy, surgery, needle stick). This is a crucial diagnostic clue.

• Differential Diagnosis: Includes venous stasis ulcers, arterial ulcers, calciphylaxis, necrotizing fasciitis, and vasculitis. The rapid onset, characteristic border, and associated systemic disease help distinguish PG.

• Histopathology: Not diagnostic, but shows a dense dermal neutrophilic infiltrate. Vasculitis is typically absent. The biopsy is primarily to rule out other conditions.

• Prognosis: Highly variable. Lesions can be recalcitrant and chronic. The course often parallels the activity of any underlying systemic disease.

• Management (Stepwise):

  1. First-line for severe disease: Systemic corticosteroids (oral prednisone or pulsed IV methylprednisolone).

  2. Steroid-sparing agents / Second-line: Cyclosporine is very effective and often used concurrently with steroids. Other options include mycophenolate mofetil, azathioprine, dapsone, or minocycline.

  3. Biologics: Anti-TNFα agents (e.g., infliximab, adalimumab) are highly effective and are often used for refractory disease or in patients with associated IBD.

  4. Topical/Wound Care: Meticulous non-adherent wound care. Topical tacrolimus or corticosteroids can be adjuncts.