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The “unusual and memorable” case reported by Ter Borg and Tersmette1 serves as a useful reminder that atypical mycobacterial infections, although uncommon, need to be considered in immunocompromised patients.
We present here two case reports of patients with pre-existing rheumatic disease receiving immunosuppressive treatment, who developed septic arthritis due to Mycobacterium avium intracellulare.
A 51 year old woman presented in 1999 with Raynaud's phenomenon, facial telangiectasia, sclerodactyly, and a positive antinuclear antibody. She complained of exertional dyspnoea, and subsequent high resolution computed tomography of the chest disclosed a ground glass appearance, indicative of active alveolitis. A diagnosis of scleroderma with interstitial lung disease was made, and treatment with prednisolone 30 mg and azathioprine 100 mg daily was started. In August 2000, she complained of pain and stiffness in the left shoulder, and this was treated with an intra-articular steroid. Six months later, she developed a left shoulder effusion, from which 50 ml of serosanguinous fluid was aspirated. Gram stain and initial bacterial cultures of the fluid were negative, and Ziehl-Neelsen stain did not show acid fast bacilli. Microscopy showed the presence of calcium hydroxyapatite crystals, and hence the shoulder was again injected with corticosteroids. Two months later, M avium was identified from the synovial fluid culture. The patient was treated with clarythromycin and ethambutol, and has made a good clinical response.
A 36 year old man presented in 1993 with arthralgia, proximal muscle weakness, and a creatine kinase of 12 000 U/l. Muscle biopsy confirmed the diagnosis of polymyositis. Treatment with prednisolone (initially 60 mg daily) and azathioprine 150 mg was started. In 1997 he developed axillary lymphadenopathy, and subsequent biopsy showed M tuberculosis. A good clinical response was achieved with rifampicin, isoniazid, and ethambutol.
In 1999 synovitis developed in the left knee and right wrist. Both joints were aspirated and injected with corticosteroids after initial Gram stain, Ziehl-Neelsen stain, and bacterial culture were negative. Eight weeks later, M avium was cultured from fluid in the left knee, and treatment with clarythromycin, ethambutol, and rifampicin was started. Histology from a right wrist tenosynovectomy six months later demonstrated granulomas, and culture confirmed the presence of M avium. At present, the patient continues to receive treatment with prednisolone 7.5 mg daily and azathioprine 150 mg daily, together with the antimycobacterial therapy, but clinical evidence of septic arthritis remains.
Infective arthritis due to M avium is rare, most commonly occurring in immunocompromised subjects, such as those receiving immunosuppressive drugs, or HIV positive patients 2. The most commonly affected joint is the knee. Up to 40% of patients with atypical mycobacterial septic arthritis have received prior intra-articular corticosteroid injection in the affected joint 3. Diagnosis of these infections rests on culture of the synovial fluid (approximately 15%), or culture of surgically obtained specimens, though the often insidious nature of the infection may lead to a delay in diagnosis of many years 3. Antimycobacterial treatment is given (dependent on sensitivities), with or without surgical synovectomy. Prognosis is variable, but most patients can expect to make reasonable or good functional recovery.
In summary, we report two cases of septic arthritis due to M avium, in patients with previously diagnosed inflammatory arthritis, who had received azathioprine and systemic and intra-articular corticosteroids. Arthritis with significant synovitis is not a common feature of dermatomyositis or scleroderma and therefore M avium should be considered as a diagnosis in patients receiving these drugs.
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