Differential diagnosis
The primary differential was focused on joint symptoms, and included disseminated gonococcal, bacterial, atypical infections, Behçet’s disease, rheumatoid arthritis, Reiter’s disease, reactive and inflammatory bowel disease (IBD)-related arthritis.
Differential diagnosis for the skin lesions included pyoderma gangrenosum, Sweets syndrome, sexually transmitted diseases, granulomatous skin lesions of inflammatory bowel disease, Reiter’s, Behçet’s, vasculitis (Wegener’s granulamatosis, polyarteritis nodosa, cryoglobulinemia), cancer (lymphoma cutis, leukemia cutis, Langerhans cell histiocytosis), infectious (sporotrichosis, blastomycosis, local fungal), drug-induced, exogenous tissue injury, vaso-occlusive (antiphospholipid-antibody syndrome).3
Further testing was necessary to determine the diagnosis.
Laboratory results
The following laboratory tests were ordered.
Blood tests. Patient’s complete blood count was remarkable for anemia and thrombocytosis; a comprehensive metabolic panel showed hypoalbuminemia. Erythrocyte sedimentation rate was elevated at 120 mm/h and C-reactive protein was elevated at 24.9 mg/L.
A diagnostic tap of the ankle showed fluid with inflammatory changes, and cultures for aerobic, anaerobic, acid fast bacilli, fungus, gonorrhea, and herpes were negative.
Joints. The patient’s joints were suspected to have septic arthritis, both clinically and on magnetic resonance imaging exam; they demonstrated no improvement of symptoms with intravenous antibiotics. Early on, the orthopedic service recommended joint debridement and open drainage.
Surgical findings included epidermolysis with subcutaneous fluid and purulent-looking material. Progressive necrosis of the debrided margins occurred over the next few days.
Workup for possible rheumatological joint disease included antinuclear antibody, rheumatoid factor, cyclic citrullinated peptide antibody (anti-CCP antibody), and human leukocyte antigens (HLA) B27 and B51. Radiographs of involved joints did not show rheumatic joint disease.
Rheumatoid arthritis was doubtful due to lack of sufficient criteria for diagnosis, and negative rheumatoid factor and anti-CCP antibody.5 HLA B27 is positive in 80% of patients with Reiter’s syndrome, 60% of those with reactive arthritis, and 50% of those with IBD arthritis.6 HLA B51, although not diagnostic, has a higher than baseline prevalence in Behçet’s disease.4 Recurrent oral aphthae, a major criteria for Behçet’s, was absent in our patient.