Use of amplified Mycobacterium tuberculosis direct test (Gen-probe Inc., San Diego, CA, USA) in the diagnosis of tubercular synovitis and early arthritis of knee joint

Osteoarticular TB specimen yield rates. Large joint analysis at a single centre

Tuberculosis (TB) remains endemic in South Africa. The spine, hip, and knee joints are common extra-pulmonary TB sites. Sound history taking, clinical examination, and basic laboratory and pathological tests remain key important steps in osteoarticular TB diagnosis. In our resources-stricken context cost is everything, if we can make a diagnosis cheaply that would go a long way. The diagnostic yield of standard laboratory tests compared to a real-time polymerase chain reaction (PCR) for osteoarticular TB diagnosis in a single orthopaedic unit has not been analysed. We conducted a retrospective record review of extra-spinal osteoarticular TB infection at our hospital from 01 June 2016 to 31 December 2021. Patient demographics, clinical history, and laboratory test results were analysed. A total of 34 cases were identified, with 32 of the cases being articular and two osseous involvement. The knee was the most common joint affected followed hip joint. Acid Fast Bacilli were detected in 32% of cases with microscopy, while TB culture was positive in 29% of samples. Histopathological examination and real-time PCR diagnosed TB in 66% and 63% of the cases, respectively. Our findings suggest that in the right context of a suggestive history and examination, histological analysis is as good as PCR for diagnosing osteoarticular TB.

HIV Infection and Osteoarticular Tuberculosis: Strange Bedfellows

We report the case of a 47-year-old female patient with rheumatoid arthritis and HIV infection presenting with a 3-week history of a painful swollen knee, increased serum inflammatory markers, and a low CD4 lymphocyte count. The diagnosis of TB arthritis was made by synovial fluid culture, GeneXpert/PCR, and confirmed by histopathology of a synovial biopsy. A mini literature review suggests that although HIV infection is associated with extrapulmonary TB, osteoarticular TB is a relatively unusual presentation in an HIV positive patient. The diagnostic utility of the GeneXpert test is explored. We also describe the patient's good response to an intra-articular corticosteroid injection in combination with standard anti-TB therapy.

The predictive value of Gen-Probe's amplified Mycobacterium tuberculosis direct test compared with culturing in paraffin-embedded lymph node tissue exhibiting granulomatous inflammation and negative acid fast stain

BACKGROUND AND OBJECTIVES

The diagnosis of granulomatous inflammation with possible tuberculosis (TB) infection in histopathology is often difficult. There is a need for a rapid and reliable diagnostic test. Thus, we evaluated the performance of the Mycobacterium tuberculosis direct (MTD) test in specimens with granulomatous lymphadenitis and negative acid fast stains.

METHODS

The M. tuberculosis direct (MTD) test by Gen-Probe was performed on 45 formalin-fixed paraffin-embedded tissue samples including 34 lymph nodes. We measured the predictive values of the MTD test in specimens with granulomatous lymphadenitis and negative acid fast stains.

RESULTS

The overall test sensitivity was 73.9%, and specificity was 95.4%. The MTD test sensitivity and specificity for lymph node tissue were 72.7% and 91.67%, respectively. In the presence of granulomatous inflammation, the MTD test sensitivity and specificity were higher than those for all tissue samples, at 75% and 100%, respectively.

CONCLUSION

Based on this study, the MTD test should be used as a supportive test in addition to conventional histochemical or immunological staining methods when evaluating lymph node tissue with a granulomatous inflammation to deliver stronger evidence to support clinical decisions at a much earlier time than a culture would allow.