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Synovial fluid genexpert quietus diagnostic jostle – A case report and algorithmic approach to monoarthritis

 Department of Clinical Immunology and Rheumatology, St John's Medical College Hospital, Bengaluru, Karnataka, India

Date of Submission07-Mar-2022
Date of Acceptance11-Apr-2022
Date of Web Publication26-Jul-2022

Correspondence Address:
Vineeta shobha,
Department of Clinical Immunology and Rheumatology, St John's Medical College Hospital, Sarjapur Road, Bengaluru - 560 034, Karnataka
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/injr.injr_46_22


Owing to the difficult anatomy, difficulty in procuring tissue samples, and clinical mimicry, the diagnosis of extrapulmonary, especially osteoarticular tuberculosis (TB), remains a challenge. Arriving at the correct diagnosis of articular TB frequently requires synovial biopsy and synovial fluid or tissue culture. Efficient utilization of rapid molecular assays such as Xpert Mycobacterium tuberculosis (MTB)/RIF assay can support the timely and accurate diagnosis. Xpert® MTB/RIF (Xpert) is a rapid, automated, nucleic acid amplification assay, recommended by the World Health Organization for the simultaneous detection of MTB complex and rifampicin resistance. Here, we report the case of long-standing inflammatory monoarthritis wherein the diagnosis took a protracted course. This case is reported to highlight that the employment of highly specific modern diagnostic technologies which are available through the Revised National TB Control Program results in swift and accurate diagnosis.

Keywords: Inflammatory monoarthritis, joint tuberculosis, Xpert® Mycobacterium tuberculosis/RIF

How to cite this URL:
Karki P, Kodali R, shobha V. Synovial fluid genexpert quietus diagnostic jostle – A case report and algorithmic approach to monoarthritis. Indian J Rheumatol [Epub ahead of print] [cited 2022 Aug 14]. Available from:

  Introduction Top

The global burden of tuberculosis (TB) has been overwhelmingly high throughout the last century and continues to pose a major public health threat, especially to the developing and underdeveloped nations. India being the second-most populous country houses one-quarter of the global TB burden.[1] As per recent national statistics, extrapulmonary TB (EPTB) accounts for 15%–20% of all cases of TB, of which skeletal TB amounts up to one-third of EPTB. Articular TB predominantly affects large joints such as the hip and knee.[2],[3] The atypical presentations of EPTB and difficulty in procuring tissue specimens can pose diagnostic challenges. Therefore, the development of schematic approaches and education at the primary care level for the early diagnosis of joint TB will be extremely useful. We present this case study and propose an algorithmic approach to monoarthritis [Figure 1] to highlight the inordinate delay in the diagnosis of joint TB which could have been easily diagnosed by the judicious application of resources available through the Revised National TB Control Program (RNTCP).
Figure 1: A schematic approach to monoarthritis in young patients

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  Case Description Top

Case presentation

A 40-year-old male presented to our tertiary care referral teaching hospital with pain and swelling of the right knee for the past 1½ years. He is a factory worker by occupation who lives more than 2000 km away. The symptoms were insidious in onset, progressed gradually and were accompanied by low-grade intermittent fever. Six months back, he was treated for respiratory tract infection with antibiotics. In addition, he had a significant weight loss of about 9 kg and loss of appetite in the past 6 months. He denied similar complaints in the left knee or any other joint. There was no history of inflammatory back pain, skin rash, orogenital ulcers, gastrointestinal, or urinary tract infection in the past or before the onset of symptoms. No past history of TB, exposure to TB, or inflammatory arthritis in the family.

On evaluation, there was evidence of right knee synovitis with terminal restriction of movement [Figure 2]. Rest of the musculoskeletal examination and systemic examination was noncontributory.
Figure 2: Right knee synovitis

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His prior set of laboratory evaluations was consistent with ongoing inflammation (erythrocyte sedimentation rate-66 mm/h and C-reactive protein (CRP)-5.29 mg/dl). Anti-citrullinated peptide antibody, rheumatoid factor, human leukocyte antigen B27, HIV, and the Mantoux test were negative. Bilateral knee X-ray was performed which showed right knee effusion and trabecular enhancement suggestive of mild juxta-articular osteopenia [Figure 3]a and [Figure 3]b consistent with synovitis which was corroborated by ultrasound examination [Figure 4].
Figure 3: (a) Bilateral X-ray of knees showing mild trabecular enhancement; (b) X-ray of right knee showing joint effusion suggestive of mild juxta-articular osteopenia seen in early synovitis

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Figure 4: Musculoskeletal ultrasonography of the right knee showing features of knee synovitis

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On synovial fluid analysis, the fluid appeared serosanguinous, total count (614 cells/cumm), neutrophils (90%), and lymphocytes (10%) suggestive of noninflammatory etiology. However, GeneXpert, a cartridge-based nucleic acid amplification test (CBNAAT), detected high titers of Mycobacterium tuberculosis (MTB), without any resistance to RIF. The patient was further evaluated to identify the primary focus of TB but was noncontributory

The patient was initiated on anti-tubercular treatment (DOTS regimen) as per RNTCP protocol. On reviewing the patient after a month, he is doing better, with decreased pain and swelling.

  Discussion Top

Diagnosis of osteoarticular TB continues to be troublesome. Traditionally, smear microscopy and cultures have been used as diagnostic modalities; however, smear microscopy has variable sensitivity (45%–80%), with poor detection in EPTB. GeneXpert for EPTB showed a sensitivity of 81.6% and a specificity of 78.9%, outperforming the conventional AFB microscopy that showed a sensitivity and specificity of 63.2% and 70.5%, respectively.[4] Conventional solid culture as well as newer liquid culture techniques have a long turnaround time of 2–6 weeks and 21 days, respectively. CBNAAT was developed for rapid detection of TB and for the identification of drug resistance. This technology permits the identification of MTB not only in the sputum, but also in extrapulmonary samples including synovial fluid. As per India TB report (2019), CBNAAT facilities for rapid diagnosis of MTB have been established at district levels and subdistrict levels (n = 1180).[5]

The Xpert MTB/RIF assay is a fully automated nucleic acid amplification test that uses a disposable cartridge with the GeneXpert Instrument System (CBNAAT). GeneXpert MTB/RIF can detect both the presence of the MTB complex genome in test specimens as well as the presence of genomic sequences of the main mutations responsible for rifampicin resistance (rpoB gene mutation). Other advantages of the Xpert MTB/RIF assay include rapidity of results (within 2 h) and minimal requirement for technical training to run the test. World Health Organization (WHO) has approved Xpert® MTB/Rif for the diagnosis of PTB, EPTB, HIV-associated TB, and TB meningitis in adults and children.[6] In a meta-analysis performed by Wen et al., the pooled sensitivity and specificity of Xpert MTB/RIF for bone and joint TB were 81% (95% confidence interval [CI], 78–83) and 83% (95% CI, 80–86), respectively.[7]

The negative predictive value (NPV) of GeneXpert MTB/RIF for extrapulmonary samples (97%) is of immense value in eliminating the diagnosis of TB. According to WHO, the NPV of GeneXpert MTB/RIF exceeds 99% regardless of the TB population prevalence rate making it possible to exclude with assurance the diagnosis of TB.[6]

The gold standard for diagnosis of tubercular synovitis remains synovial histopathology. In comparison to histopathology, the Xpert MTB/RIF assay has a sensitivity and specificity of 79.3% (73.5–85.1%) and 73.7% (67.8–79.6%), respectively.[8] Therefore, although arthroscopic synovial biopsy gives the definite diagnosis for osteoarticular TB, the easy availability, noninvasive technology, and rapid turnaround time make GeneXpert MTB/RIF the investigation of choice. Further, the synovial fluid is rather easy to aspirate from large joints either as a blind procedure or under ultrasound guidance in an outpatient setting. The synovial fluid perse, the detection rates for acid-fast bacilli are quite low 10%–20%, and cytological examinations are rather noninflammatory and unable to point toward a diagnosis or differentials.[9] Further, the conventional radiologic or ultrasound examination or magnetic resonance imaging of affected joints also reveals rather nonspecific changes.

  Conclusion Top

In our case report, the synovial fluid aspiration was noninflammatory; however, the Genexpert clinched the diagnosis. We have proposed an algorithmic approach and emphasized the application of modern diagnostic technologies such as Genexpert for an accurate diagnosis.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient (s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

INDEX-TB Guidelines: Ministry of Health and Family Welfare [Internet]. Available from: [Last accessed on 2022 Mar 06].  Back to cited text no. 1
Sharma SK, Mohan A, Kohli M. Extrapulmonary tuberculosis. Expert Rev Respir Med 2021;15:931-48.  Back to cited text no. 2
García-Arias M, Pérez-Esteban S, Castañeda S. Septic arthritis and tuberculosis arthritis. J Arthritis 2012;01:1-10.  Back to cited text no. 3
Elbrolosy AM, El Helbawy RH, Mansour OM, Latif RA. Diagnostic utility of GeneXpert MTB/RIF assay versus conventional methods for diagnosis of pulmonary and extra-pulmonary tuberculosis. BMC Microbiol 2021;21:144.  Back to cited text no. 4
Division Welfare CT. India TB Report 2019. Welfare, Ministry of Health and Family; 2019. p. 244.  Back to cited text no. 5
Automated Real-Time Nucleic Acid Amplification Technology for Rapid and Simultaneous Detection of Tuberculosis and Rifampicin Resistance: Xpert MTB/RIF Assay for the Diagnosis of Pulmonary and Extrapulmonary TB in Adults and Children: Policy Update. Available from: [Last accessed on 2022 Mar 03].  Back to cited text no. 6
Wen H, Li P, Ma H, Lv G. Diagnostic accuracy of Xpert MTB/RIF assay for musculoskeletal tuberculosis: A meta-analysis. Infect Drug Resist 2017;10:299-305.  Back to cited text no. 7
Zhou Z, Zheng Y, Wang L. Diagnostic accuracy of the Xpert MTB/RIF assay for bone and joint tuberculosis using tissue specimens. Int J Infect Dis 2021;105:224-9.  Back to cited text no. 8
Neuberger A, Sprecher H, Oren I. Septic arthritis caused by Mycobacterium kansasii in a prosthetic knee joint. J Clin Microbiol 2006;44:2648-9.  Back to cited text no. 9


  [Figure 1], [Figure 2], [Figure 3], [Figure 4]


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