Multifocal osteoarticular tuberculosis in a systemic lupus erythematosus (SLE) patient: a rarity or an underdiagnosed condition?

Tuberculosis (TB) and its association with rheumatic diseases have been widely recognised. Occurrence of multifocal skeletal involvement constitutes <5% of all skeletal TB cases. We present a Malay patient with multifocal osteoarticular TB (OATB). A 35 year-old SLE woman with background usage of corticosteroid therapy and Azathioprine presented with lupus nephritis flare. Renal biopsy revealed diffuse proliferative lupus nephritis and intravenous (IV) Cyclophosphamide 0.5 g/m (850 mg) was initiated. One week later, patient complained dorsum of left hand and right knee swelling. On physical examination, patient was afebrile and the left hand swelling was cystic in consistency while right knee was warm and tender. Erythrocyte Sedimentation Rate (ESR) was 50 mm/hr and C-Reactive Protein (CRP) was 9.4 mg/L. Her Mantoux test was positive with 20 mm induration. Wrist radiograph and chest radiograph was normal. Musculoskeletal ultrasound showed 4th extensor compartment tenosynovitis with Doppler signal and right knee effusion with synovial proliferation. Extensor tenosynovectomy and right knee aspiration was performed. Left hand excised tissue and right knee synovial fluid for acid-fast bacilli (AFB) stain, TB PCR, bacterial and fungal cultures were negative. Urgent histopathological examination of the excised tissue showed necrotising granulomatous inflammation. Patient was empirically started on TB treatment and subsequent mycobacterial culture confirmed the diagnosis of TB. The joints swelling resolved after one month of TB treatment. Multifocal OATB is an infrequent form of extrapulmonary TB and diagnosing OATB requires high index of suspicion particularly in SLE patient on immunosuppression. Prompt investigations are essential to the diagnosis of this rare condition for early initiation of anti-tuberculous therapy.