Tuberculous arthritis involving the ankle joint was found to mimic rheumatoid arthritis (RA) in a patient with lupus nephritis, according to findings of a case study published in Clinical Medicine.

A 45-year-old woman with lupus nephritis presented with symptoms of pain and swelling over her left ankle and right wrist joint for the previous 4 months. The swelling progressively increased in size and was associated with morning stiffness. The patient denied fever, cough, or other systemic symptoms and had no contact with a tuberculosis patient. She had a history of hypertension, uterine fibroid, and class 4 lupus nephritis. She was also receiving a regimen of diltiazem, azathioprine, mycophenolate mofetil, hydroxychloroquine, prednisolone 10 mg daily, alfacalcidol, and losartan.

Physical examination showed evidence of a 6×8 cm swelling over the left ankle joint, and swelling over the right wrist and the second to fifth metacarpophalangeal joint over the right hand. On imaging, synovial hypertrophy with calcification and severe structural deformity and active synovitis were seen over the left foot, and joint erosion and effusion were reported over the right second to fifth metacarpophalangeal joint and bilateral wrist joints. Laboratory tests revealed a white cell count of 11.7×109/L, C-reactive protein of 31.4 mg/L, erythrocyte sedimentation rate of 48 mm/hour, and normal renal and liver function tests.


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With the assumption that this was a case of RA, treatment with methotrexate 15 mg/week was initiated. However, there was no improvement in the left ankle after 4 months of methotrexate therapy. Magnetic resonance imaging (MRI) of the left ankle showed increased joint effusions with synovial proliferation, especially in the intercarpal, carpal-metacarpal, and subtalar joints, with thickened synovium and extensive bone erosions.

Because of a lack of response to methotrexate and a negative anticitrullinated protein antibody test, aspiration of the left ankle joint was done, with evidence suggestive of acute suppurative inflammation. Empiric treatment for septic arthritis with cefazolin was initiated. A tuberculin skin test was strongly positive. After 5 days of antibiotics, there was no evidence of growth on the bacterial culture, but the molecular tuberculosis genome test was positive for Mycobacterium tuberculosis. The patient subsequently received a quadruple therapy of rifampicin, isoniazid, ethambutol, and pyrazinamide for 2 months, followed by maintenance phase of isoniazid and rifampicin for 7 months.

The swelling markedly reduced with this treatment regimen, but the left ankle deformity remained.

The authors of the case report noted that a diagnostic delay occurred because the patient was thought to have a case of RA or lupus-related inflammatory arthritis. The patient received a bacillus Calmette-Guerin (BCG) vaccine during childhood and denied any previous contact with a tuberculosis patient; however, the diagnosis of tuberculosis should always be considered in endemic regions. While MRI is useful for differentiating between tuberculous arthritis and RA, it is not diagnostic and a biopsy is required to confirm the diagnosis.

“The diagnosis of tuberculous arthritis is difficult in patients with [systemic lupus erythematosus] as there are many overlapping features in between the two. In addition, the typical presentation of tuberculosis might not be present, especially in an immunocompromised patient. Hence, the diagnosis of [tuberculosis] should always be considered in cases with chronic arthritis especially in endemic area,” the authors wrote.

Reference

bin Ismail MN, Ab Rahim SM. Tuberculous arthritis of the ankle joint masquerading as rheumatoid arthritis in a patient with lupus nephritis. Clin Med (Lond). 2021;21(1):e108-e109. doi:10.7861/clinmed.2020-0882