KEY POINTS

• Joint tuberculosis (TB) is an uncommon manifestation of TB that typically presents with subacute or chronic atraumatic inflammatory symptoms in single, large, weight-bearing joints.

• In Canada, epidemiological risk factors for TB include extended time spent in countries with high burden of TB, known exposure to TB or being part of a population disproportionately affected by TB (e.g., people born outside of Canada, those of Indigenous ethnicity or those with a history of homelessness or incarceration).

• Synovial thickening, joint effusions, juxta-articular osteopenia, peripheral osseous erosions and gradual joint space narrowing on magnetic resonance imaging or computed tomography are suggestive of joint TB.

• Specialized mycobacterial culture is the gold standard for diagnosis of TB, but nucleic acid amplification tests are increasingly accessible and allow for rapid diagnosis of joint TB.

• Treatment for joint TB should be started promptly for preservation of joint function and prevention of irreversible destruction.

A 47-year-old man presented to the emergency department with 2 weeks of acute-on-chronic pain in his right knee. He described a 5-year history of chronic pain in his right knee, with 1 flare-up 3 years before presentation, which had resolved after a few weeks of ibuprofen use. He had not previously sought care for this problem. He was otherwise healthy, with no chronic medical conditions or previous surgeries, and he tested negative for HIV. He had smoked crystal methamphetamine daily for the last 10 years and had no history of intravenous drug use. He had immigrated from the Philippines 16 years before and had not returned.

When examined, the patient was afebrile with normal vital signs. His right knee was swollen with limited flexion and extension. He did not have any overlying erythema or tenderness to palpation of the bursa or the joint line. He had no other inflamed joints. Initial laboratory results showed a leukocyte count of 8.4 (normal 4–11) × 10⁹/L and an elevated C-reactive protein level of 34.4 (normal < 3.1) mg/L. A radiograph of the patient’s right knee showed bony destruction of the knee joint and an irregular lucency of the medial tibial plateau (Figure 1). A computed tomography (CT) scan showed cortical destruction with peripheral osseous erosions and juxta-articular osteopenia (Figure 2). The patient was admitted to the internal medicine service and the initial treating physicians were concerned that he may have had a malignant disease; they ordered a CT scan of the chest, abdomen and pelvis, which showed mild, biapical lung scarring (Figure 3).

<a href=”https://www.cmaj.ca/content/cmaj/195/22/E782/F1.large.jpg?width=800&height=600&carousel=1″ title=”Radiograph of the right knee joint of a 47-year-old man with joint tuberculosis, showing peripheral osseous erosions (red arrow), irregular lucency of the medial tibial plateau (yellow arrow) and joint space narrowing (white arrow).” class=”highwire-fragment fragment-images colorbox-load” rel=”gallery-fragment-images-1137217360″ data-figure-caption=”

Radiograph of the right knee joint of a 47-year-old man with joint tuberculosis, showing peripheral osseous erosions (red arrow), irregular lucency of the medial tibial plateau (yellow arrow) and joint space narrowing (white arrow).

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Figure 1:

Radiograph of the right knee joint of a 47-year-old man with joint tuberculosis, showing peripheral osseous erosions (red arrow), irregular lucency of the medial tibial plateau (yellow arrow) and joint space narrowing (white arrow).

Bloody synovial fluid was aspirated from the patient’s right knee joint, with a leukocyte count of 36.7 × 10⁹/L (79% neutrophils, 15% lymphocytes, 6% monomacrophages) and an erythrocyte count of 150 × 10⁹/L, and no crystals or organisms on Gram stain. Cultures for mycobacteria were negative on acid-fast bacilli staining. Given these findings, bacterial septic arthritis was suspected and he was treated with empirical antibiotic therapy (intravenous [IV] ceftriaxone 2 g daily, and IV vancomycin with a target trough of 10–20 mg/L). After 6 days, the patient’s knee had not improved and bacterial cultures from synovial fluid remained negative. The internal medicine team consulted our infectious diseases team.

We suspected tuberculosis (TB) based on 3 factors, namely the chronic nature of the monoarthritis, the pulmonary apical scarring on chest imaging and that the patient had emigrated from the Philippines — designated as a country with a high burden of TB by the World Health Organization (WHO), with the fourth highest national incidence of TB globally.1 We identified no other identifiable risk factors for TB, such as previous incarceration, homelessness or known close contact with someone with TB.

Nucleic acid amplification testing (NAAT) for TB using the GeneXpert MTB/RIF Ultra assay (Cephied) was performed on samples of synovial fluid, which confirmed the presence of Mycobacterium tuberculosis. Smear testing of sputum samples were negative for acid-fast bacilli. We prescribed standard weight-based dosages of rifampin (10 mg/kg/d), isoniazid (5 mg/kg/d) with pyridoxine (25 mg/d), pyrazinamide (25 mg/kg/d) and ethambutol (15 mg/kg/d) and discharged him to continue this therapy under care of the provincial TB program.

Four weeks later, samples of the patient’s synovial fluid showed growth of M. tuberculosis that was susceptible to the first-line anti-TB medications he was receiving. Mycobacterial cultures from sputum samples were negative, suggesting that he did not have pulmonary TB. At follow-up after the 9-month course of treatment, the patient had considerable improvement of his knee pain (pain only with extended use), periarticular and lower leg swelling and range of motion (full flexion and extension). He had returned to work and was ambulating without need for a mobility aid. Given the extensive destruction of the knee joint, we had planned to refer him to an orthopedic surgeon for consideration of knee arthroplasty. However, he was lost to follow-up, and subsequent knee imaging and surgical referral could not be completed.

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