Immunosuppressed patient with a non-healing ulcer and diagnostic uncertainty
A 67-year-old man with a 10-year history of rheumatoid arthritis on methotrexate and prednisolone 10 mg daily presents with a 3-month non-healing ulcer on the left shin, 3 cm with raised, violaceous, indurated borders and a granulating base. He has no fever. He reports weight loss of 4 kg over 3 months. Examination shows no lymphadenopathy; the ulcer is not tender. A wound swab grew Staphylococcus aureus. He has been treated with two courses of oral antibiotics without improvement.
1. What is the differential diagnosis, and which features are most concerning?
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The differential for a chronic non-healing ulcer in an immunosuppressed patient includes:
- Malignancy: squamous cell carcinoma (especially in immunosuppressed patients), basal cell carcinoma, or lymphoma; the raised, indurated, violaceous border and lack of response to antibiotics are concerning.
- Infection: atypical mycobacteria, deep fungal infection, or chronic bacterial infection; the S. aureus may be colonization rather than the cause.
- Inflammatory/vasculitic: pyoderma gangrenosum (often painful, violaceous undermined border, associated with inflammatory disease), or vasculitis.
- Other: venous or arterial ulcer (less likely given the appearance), or a drug-related ulcer.
Most concerning features: the raised, indurated, violaceous border, weight loss, immunosuppression, and failure to respond to antibiotics. These raise suspicion for malignancy or atypical infection and mandate biopsy.
2. What investigations would you arrange, and how would you manage the immunosuppression?
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Investigations:
- Skin biopsy for histopathology, special stains (PAS, Ziehl-Neelsen, Gram), and tissue culture (bacterial, mycobacterial, fungal). This is the key investigation; a superficial swab is insufficient.
- Bloods: FBC, CRP, U&E, LFTs, and consider HIV and hepatitis serology if not done.
- Imaging: if malignancy or deep infection suspected, consider ultrasound or MRI of the area, and staging investigations if malignancy confirmed.
Management of immunosuppression:
- Do not stop methotrexate or prednisolone abruptly without specialist input; discuss with rheumatology. However, if malignancy or serious infection is suspected, reduce or hold immunosuppression in consultation with the rheumatologist, balancing the risk of disease flare.
- Treat any identified infection with appropriate antimicrobials based on culture and sensitivity.
- If malignancy is confirmed, refer to oncology/dermatologic surgery and coordinate care.
- Provide wound care and analgesia; involve the multidisciplinary team (dermatology, rheumatology, oncology, plastic surgery).
Follow-up: review after biopsy results; if pyoderma gangrenosum is diagnosed, consider systemic therapy (e.g., corticosteroids, ciclosporin) with specialist input.