Gene Xpert MTB / RIF – Diagnostic Role in Tuberculous Pleurisy

Background: Tuberculous pleurisy is a common extrapulmonary manifestation and is second to tuberculous lymphadenitis. Due to its paucibacillary in origin, its diagnosis is a challenge. Furthermore, it is also complicated by the emergence of MDR. Gene Xpert MTB/RIF is a new rapid promising innovation for the detection of mycobacterium tuberculosis and its resistance to Rifampicin, giving result within two hours. Objective: To evaluate the diagnostic role of Gene Xpert MTB/RIF in suspected cases of tuberculous pleurisy. Study Design: Cross sectional study. Study Setting: Institute of Chest Medicine Mayo Hospital – a Tertiary Care Hospital affiliated with King Edward Medical University, Lahore. Methodology: The study group, one hundred (M-60 Conflict of Interest: No


Introduction
Worldwide, Tuberculosis (TB) is an important leading cause of morbidity and mortality.It is a common public health disease with one third of world's population infected with it. 1Developing countries have 90% of the burden of TB. 2 TB manifests itself with involvement of pleura or lymph nodes in 25% of TB patients. 3uberculous pleural effusion has been reported as the most common form of extra pulmonary tuberculosis in certain areas of India but worldwide pleural TB is the second commonest manifestation of extra pulmonary TB. 4 Pleural disease in TB patient's is higher in developing countries constituting 30%, as compared to European countries where it is 3 -5%. 5,6Pleural TB was detected in 82% of all pleural effusions in Rawanda study 7 and 91% of exudative pleural effusions in a study conducted in Uganda. 8iagnosis of tuberculous pleural effusion is a challenge due to poor sensitivity of conventional dia-

Original Article
gnostic methods and increasing drug resistance.Pleural tissue culture of MTB or histopathologygold standard for diagnosis has variable sensitivity ranging from 40 -80% for pleural tissue culture and 50 -97% for histopathology. 9Pleural biopsy either by Abrahm's needle or by Thoracoscopy is an invasive procedure that needs skill and equipment which are not available in many health centres.The tissue culture on Lowenstein Johnson (L.J) solid medium takes up to 8 weeks and six weeks on liquid medium to get final result. 10o reduce morbidity and mortality, rapid diagnosis of Pleural TB is needed.The newer serological tests like interferon gamma release assays do differentiate between latent and active TB infection. 11More rapid tests such as nucleic acid amplification provides timely and definitive diagnosis of pleural tuberculosis.Gene Xpert MTB/RIF is an integrated fully automated specimen processing real time nucleic acid amplification test which detects Mycobacteria tuberculosis (MTB) and rifampicin resistance within two hours. 12,13ene Xpert MTB / RIF is a promising innovation having high sensitivity, specificity and rapid result. 14][17] This studywas undertaken to evaluate the possible utility of Xpert MTB / RIF as an option for an accurate and timely diagnosis of Pleural TB in a tertiary health care setting.

Objective
To evaluate the diagnostic role of Gene Xpert MTB / RIF in the diagnosis of tuberculous pleurisy.Study Design: Cross sectional study.Study Setting: Institute of Chest Medicine, Mayo Hospital.A Tertiary Care hospital affiliated with King Edward Medical University Lahore.

Subjects and Methods
Randomized one hundred patients of exudative, predominantly lymphocytic pleural effusion who have strong suspicion of tuberculosis etiology were included in the study.Only adult without any gender discrimination patients were enrolled in the study.10cc pleural fluid aspirated with patient consent and sent to PMRC TB Research Centre (Pakistan Medical TB Research Centre) affiliated with Mayo Hospital, for Gene Xpert MTB / RIF.

Laboratory Procedure
First of all, the fluid was centrifuged at 3000 RPm for 15 minutes.The supernatant was discarded and the sediment was processed forGene Xpert MTB / RIF test.Lysing agent was added to the sediment in a ratio of 2:1 and kept for 15 minutes.During this period, the sample was shaked vigorously twicely.Later on 2ml sediment was transferred to Gene Xpert cartridge and cartridge was placed in Gene Xpert instrument which gave result within 2 hours.Patients having expectoration also examined for AFB smear and culture to document the associated parenchymal disease.

Results
One hundred cases (male 60, female 40) of exudative predominantly lymphocytic pleural effusion who have strong suspicion of tuberculous etiology were included in the study.Males aged between 22 -73 years and females between 14 -64 years (Table 1).Bioche- mistry and lymphocyte counts were described in Table 2 and 3. Two cases have AFB smear positive and culture was also positive in 1% (Table 4).Chest radiology represented right sided pleural effusion in 73%, left sided pleural effusion in 25% and bilateral effusion in 2% cases (Table 5).Gene Xpert detected MTB in 12% cases and Rifampacin resistance in 6% cases (Table 6).

Discussion
Pleural effusion is second to lymphatic involvement in extrapulmonary tuberculous manifestations.It may occur either as primary or as a reactivation disease. 18,19Tuberculous pleurisy which was thought to result due to pure delayed hyper sensitivity reaction is now believed to be the direct infection of pleura with Mycobacterium tuberculosis resulting in lymphocytic driven immunological response.Detection of Mycobacterium tuberculosis in the pleural fluid, pleural biopsy tissue either by microscopy or culture and demonstration of granulomatous lesion with caseation, is the gold standard for the diagnosis of tuberculous pleurisy. 20,21Gene Xpert MTB/RIF is a new technique to detect mycobacterium tuberculosis and its resistance to Rifampicin, which gives results within two hours.
Our study results showed MTB detection in 12 (12%) cases (Male 8 (13.13%) and female 4 (10%).Out of 12 (12%) MTB detected patients, 6 (6%) cases (Male 2 (3.3%) and Female 4 (10%) have Rifampicin resistance.So this testing not only confirmed the diagnosis of tuberculous pleurisy but also lead to detection of drug resistance.So it was possible to start drug resistance treatment at an early stage.2% of the study cases also have positive microscopy for AFB and 1% has also culture positive for AFB which confirmed the associated parenchymal disease.Parenchymal disease co-exists with pleural effusion in 20% chest X-rays and 80% on CT Chest. 22All smear positive and culture positive cases have positive Gene Xpert MTB.Randomized registered study cases showed that right sided pleural effusion (73%) was more frequent as compared to left sided effusion (25%).Bilateral pleurisy was a rare manifestation.
Study by Sahn SA et al concluded that one third of pleural effusions can be diagnosed by pleural fluid analysis alone where no other technique / method is used for confirmation of tuberculous pleurisy. 23mparing Gene Xpert results with a local study by Javed N et al, where it was 8% positivity for MTB detection. 24This study also had pleural biopsy which was positive in 14% cases representing granulomatous lesions with caseous necrosis.Other international studies like Vadwair Vetal, 25 Friedrich SOI etal, 26 Christopher DJ etal 27 and John K etal 28 showed sensitivity and specificity on pleural fluid as 63% and 100%, 25% and 100%.16% and 100% and 28.7% and 96.6% specificity respectively.So different studies have different sensitivity results but specificity is the same i.e. 100%.
Analyzing the above studies results which have sensitivity between 8% to 63% and specificity between 96.6% to 100%, this rapid technique of MTB/RIF.detection can be used to diagnosis TB pleurisy.This rapid non invasive technique not only helped to confirm the diagnosis but also lead to detect drug resistance at an early stage to start treatment of MDR TB.

Conclusion
Xpert MTB / RIF is a useful rapid technique to diagnose tuberculous pleurisy.Although at present, it has limited availability and utility.

Table 1 :
Study Patients (Gender and Demographic Characteristics).

Table 4 :
AFB Smear and Culture.