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We present the rare case of a 60 year old man with Mycobacterium kansasii infection who complained of severe joint pain and swelling, predominantly of the right shoulder. Non-steroidal anti-inflammatory drugs (NSAIDs) led to pain relief. The swelling around the right shoulder was unsuccessfully treated by aspiration followed by surgery.
As a steam engine driver the patient was exposed to asbestos and inorganic dusts (coal, mineral/silicate). The rheumatological examination disclosed a mobile, firm, elastic swelling over the dorsal aspect of the left elbow, tenderness and mild swelling of both wrists, the metacarpophalangeal (MCP) joints, the third fingers of both hands, and the MCP joints of both thumbs. Joint effusion was palpated around the right shoulder and mobility was limited owing to pain. Inflammatory measures were raised and angiotensin converting enzyme was within normal range. No evidence of acid fast rods in the urine, the bronchial fluid, or aspirated joint fluid (right shoulder) was found.
The radiographs and the magnetic resonance imaging findings (figs 1A and B) of the right shoulder showed erosions of the acromioclavicular joint and the humerus consistent with rheumatoid arthritis, as well as degenerative changes. Hands and elbows were radiologically normal.
Initially, because of a suspicion of pneumoconiosis and clinical signs of rheumatoid arthritis, the preferred diagnosis was Caplan’s syndrome—a form of rheumatoid arthritis marked by the intercurrent onset of polyarthritis and pneumoconiosis (usually silicosis), but x ray examination and computed tomography of the thorax showed postinflammatory changes in the right upper lung field, bullae in the left lung, and pleural thickening with characteristic asbestos related plaques without signs of silicosis (fig 1C).
Histology displayed ill-defined epithelioid granulomas and chronic fibrous synovialitis (fig 1D), therefore sarcoidosis was also considered but thought unlikely in view of an unremarkable CD4/CD8 ratio in the bronchial fluid, normal angiotensin converting enzyme values, and the absence of small joint involvement.
In the presence of undifferentiated autoantibody phenomena and raised inflammatory variables (table 1) without convincing evidence for sarcoidosis or acute tuberculosis, early undifferentiated connective tissue disease was diagnosed and treatment with azathioprine and prednisolone was started under isoniazid cover (considering a positive Multimerieux tuberculin test).
Surprisingly, after three weeks Mycobacteria were cultured in the fluid from the right shoulder and characterised as M kansasii (16S rRNA gene sequencing). As recommended, the patient was prescribed a triple combination of isoniazid (300 mg/daily), rifampicin (600 mg/daily), and ethambutol (3×500 mg/daily) for 18 months and the firm swelling around the left elbow and autoantibody phenomena resolved completely. Azathioprine was discontinued, prednisolone reduced.
Today (2 years after completing treatment) the patient reports occasional arthralgia of the shoulder joints, interpreted as degenerative changes and responding to NSAIDs.
M kansasii was first described by Buhler and Pollack in 1953. Infections with M kansasii are environmentally acquired. Interestingly, M kansasii is primarily restricted to tap water and can survive for up to 12 months.1,2 Usually M kansasii affects the lungs similarly to tuberculosis and rarely affects joints, tendons or bone.3,4
Among the non-tuberculous Mycobacteria, M kansasii is the commonest cause of monarthritis, usually exhibiting erosive changes.5,6 Tests for acid fast rods in synovial fluid are often negative. Overall, only 50 cases of M kansasii arthritis have been described during the past 40 years. About one half of the patients had underlying disorders (for example, HIV, rheumatic diseases), and for some a previous joint puncture (iatrogenic infection) or trauma may be suspected as the probable route of entry.3 In the case described here, the infection had been preceded by punctures of the shoulder joint, although haematogenic spread cannot be ruled out completely because of postinflammatory changes in the right upper lobe.
In conclusion, care must be taken not to overlook an infection with atypical Mycobacteria in polyarthritis with erosive changes.
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