Diagnostic Algorithm for EPTB

It is crucial to make an effort for microbiological confirmation in presumptive Extrapulmonary Tuberculosis (EPTB) cases. Appropriate specimens from the Extrapulmonary (EP) site are collected and, depending on the specimen type and availability of facilities, the specimens are sent for:

• Cartridge-based Nucleic Acid Amplification Testing (CBNAAT)
• Culture and Drug Susceptibility Testing (C&DST) for M. tuberculosis 
• Histopathological examination

The diagnostic algorithm (see the figure below) to be followed for EPTB cases depends on 2 main factors:

1. Availability of appropriate specimens from the EP site
2. Availability of CBNAAT (preferred test)

Figure: Diagnostic Algorithm of EPTB

• If an appropriate specimen from the EP site is available, specimens from the presumed sites of involvement must be tested with CBNAAT.
• CBNAAT detects MTB and RIF status and helps to identify microbiologically confirmed EPTB cases.
• If CBNAAT is not available, the specimen is sent for Liquid Culture (LC) at the C&DST lab. If the LC is positive, it is identified as a microbiologically confirmed EPTB case.
• If there is high clinical suspicion of TB even after a negative culture result, other diagnostic tools are used to clinically diagnose EPTB (usually with a specialist). If these tests indicate TB, they may be treated as clinically diagnosed EPTB or else arrive at an alternate diagnosis.

Clinical Diagnosis of EP-TB

If an appropriate specimen from the EP site is not available, in the presence of high clinical suspicion of TB, other modalities of diagnosis are used in consultation with a specialist. If with other diagnostic modalities, TB diagnosis still cannot be established, the specialist may explore an alternate diagnosis. 

A clinical diagnosis of EPTB is made if a consultative decision is made to treat with a full course of anti-TB drugs in spite of the situations listed above. Chest X-ray (CXR), ultrasonography, Computerised Tomography (CT) scan, Magnetic Resonance Imaging (MRI) and biochemical examinations are supporting tests that can be used to help arrive at a diagnosis.

Resources

• Training Modules (1-4) for Programme Managers and Medical Officers, 2020.
• Technical Operational Guidelines, Chapter 3: Case Finding and Diagnosis Strategy, NTEP.

Assessment

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