Title: Tuberculosis: Pathophysiology and Diagnosis
1TuberculosisPathophysiology and diagnosis
Dr. Aditya Jindal Interventional Pulmonologist
Intensivist Jindal Clinics SCO 21, Sec 20D,
Chandigarh DM Pulmonary and Critical Care
Medicine (PGI Chandigarh), FCCP
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3Course of TB infection
4Types of TB
- Primary tuberculosis
- is a form of disease that develops in a
previously unexposed and therefore unsensitized
person - Secondary tuberculosis
- is the pattern of disease that arises in
previously sensitized or infected host.
5Primary TB
- Infection of an individual who has not been
previously infected or immunized. - The inhaled bacilli implant in the distal
airspaces of lower part of upper lobe or upper
part of lower lobe close to the pleura - As sensitization develops, a gray-white
inflammatory consolidation is formed? Ghon focus
6Sites of Primary TB
- Most common - Lungs
- Other sites Tonsils, adenoids
- Site of BCG
vaccination - GIT ileum, colon etc
- GUT
7Ghons complex
- Consists of 2 components
- Pulmonary component
- lesion in the lung (Ghon focus or primary focus)
- 1-2cm solitary area located peripherally in the
subpleural focus in the lower part of upper lobe
or upper part of lower lobe - Micro the lung lesion show tuberculous granuloma
with caseous necrosis - Lymphatic component
- lymphatics draining lung lesion containing
phagocytes with M. tuberculosis bacilli
8Ghon complex
9Fate of Primary complex
- Heal by fibrosis? calcification
- Progressive primary tuberculosis
- Primary miliary tuberculosis
10Secondary TB
- The infection of an individual who has been
previously infected or sensitized - The infection may be acquired from
- Endogenous source ? reactivation of dormant
primary complex - Exogenous source
11Pathological lesions of Secondary TB
- The initial lesion is a small focus of
consolidation of lt2cm in diameter within 1 to 2cm
of apical pleura - Gross sharply circumscribed, firm, gray white to
yellow with variable amount of central caseation
necrosis - Micro coalescent tuberculous granulomas with
central caseation necrosis.
12Fate of secondary TB
- The lesion may heal with fibrous scarring and
calcification - Fibrocaseous tuberculosis (progressive pulmonary
TB ) - Tuberculous caseous pneumonia
- Miliary tuberculosis
13Pathology of TB
- Granuloma formation is the hall-mark of pathology
of TB - Granuloma is a
- i. Rounded tight collection of chronic
inflammatory cells - ii. Central Caseous necrosis
- iii. Active macrophages - epithelioid
cells - iv. Outer layer of lymphocytes
fibroblasts - v. Langhans giant cells joined
epithelioid cells
14TB Pathology
- Bacterial entry
- T Lymphocytes.
- Macrophages.
- Epithelioid cells.
- Proliferation.
- Central Necrosis.
- Giant cell formation.
- Fibrosis.
15Granuloma Histopathology
16Caseation necrosis
17Causes of granuloma formation
- Tuberculosis
- Other mycobacterial infections, Leprosy
- Bacterial infections Brucellosis
- Other infections Fungal, viral, protozoal
- Non-infectious causes
- - Sarcoidosis
- - Foreign bodies
- - Lymphomas
18Miliary TB
- Occurs when organisms drain through lymphatics
into? lymphatic ducts? venous return on the right
side of heart? pulmonary arteries - Individual lesions are either microscopic or
small, visible (2mm) foci of yellow-white
consolidation scattered through the lung
parenchyma (resembling millet seeds) - Micro the lesion shows structure of granuloma
with minute areas of caseous necrosis.
19Miliary TB
20Course of TB infection
21Tuberculosis
22- Clinical Features
- Sputum Examination
- Chest Radiology
- Bronchoscopy
- Mantoux test
- Indirect laboratory tests
23Clinical Symptoms
- Prolonged fever, malaise, weakness, wt. loss etc.
- Pulmonary Cough, sputum, haemoptysis
persistent - Lymphadenopathy, organ enlargement, others
24- Clinical Features
- Sputum Examination
- Mantoux test
- Chest Radiology
- Bronchoscopy
- Indirect laboratory tests
25Sputum examination
- Smear examination (Sputum, other secretions)
- Auramine- Rhodamine staining
- Culture of material/ tissues
26Myco-bacteria
- Myco (fungus like) Bacterium (bacteria)
- Ability to resist decolourization by a weak
mineral acid after staining with an aryl-methane
dyes (acid-fastness) - Slender, straight or slightly curved, rod shaped
- Length 2-4 u, Breadth 0.2-0.8 u
- Occur singly, in pairs or small groups
- Long, filamentous, club-shaped (rarely branching)
27MYCOBACTERIAL DEMONSTRATION
- Smear Easiest, quickest
- Requires gt 10000 AFB/ml
- Sensitivity 50-60
Specificity High - Culture More sensitive 10 AFB/ml
- Traditional 6-8 wks
- Septi Chek Biphasic High
yield - Radiometric BACTEC
- Others
- Animal pathogenicity
- Antimicrobial sensitivity
28M tb in sputum smear
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30- Rapid culture methods
- BACTEC system
- MycobactGrowth Indicator Tube(MGIT)
- MB/BacT system
- Septi-chek
- ESP culture system
- Microscopic observation of broth/slide cultures
31M tb Colonies on culture (LJ medium)
32- BACTEC System
- Radiometric method
- 14C labelled palmitic acid added to liquid 7H12
medium - Detects MTB by metabolism rather than growth
- 14CO2 produced detected
- Growth index(GI) measured
- Results available in 7-14 days (87-96)
33- MGIT
- Automated system
- Capable of analyzing 960 specimens
- Metabolism of MTB produces O2
- Fluorescence of dye with oxygen measured
- Results available in 7-14 days
- Cost effective for high load micro labs
34- Clinical Features
- Sputum Examination
- Chest Radiology
- Bronchoscopy
- Mantoux test
- Indirect laboratory tests
35Chest radiology
- I. Chest Upper Lobes/Diffuse miliary
- Infiltrates/Exudates/Fibrosis
- Multiple, thin walled cavities
- Lymphadenopathy,
Pl.effusion - II. Others Enlargement of organs
- Erosions/Effusions
- Caseations/collections
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40Role of Chest X-ray
- No chest X-ray pattern is absolutely typical of
TB - 10-15 of culture-positive TB patients not
diagnosed by X-ray - 40 of patients diagnosed as having TB on the
basis of x-ray alone do not have active TB
X-ray is unreliable for diagnosing and monitoring
treatment of tuberculosis
41- Clinical Features
- Sputum Examination
- Chest Radiology
- Bronchoscopy
- Mantoux test
- Indirect laboratory tests
42Role of bronchoscopy
- Valuable in early diagnosis of strongly suspected
sputum-negative TB - Diagnosis of endobronchial TB/miliary TB
- TBLB yield is greater (82) than BAL (26)
- TBNA has a role in mediastinal lymph nodal
tuberculosis with negative sputum smears
43ESR?
44- Clinical Features
- Sputum Examination
- Chest Radiology
- Bronchoscopy
- Mantoux test
- Indirect laboratory tests
45Tuberculin (Mantoux) Test
- Infection with mycobacterium tuberculosis leads
to delayed hypersensitivity reaction which can be
detected by Mantoux test - About 2 to 4 weeks after infection
- Intracutaneous injection of purified protein
derivative (PPD) of M.tuberculosis - Induces a visible and palpable induration that
peaks in 48 to 72 hours
46How to do the test?
- Sub cutaneous
- Weal formation
- Itching no scratch
- Read after 72 hours
- Induration size.
- 5-10-15mm
47Positive test
48Interpretation
- Induration less than 5 mm gt no exposure to
tubercular bacilli - Induration between 5-9 mm gt this can be due to
atypical mycobacteria or BCG vaccination. It may
suggest infection in immunocompromised children
such as HIV infection or other immunosuppression - Induation 10 mm or more gt in a child with
symptoms of tuberculosis should be interpreted as
tubercular disease
49Clinical significance
- Denotes infection
- Does not differentiate infection from active
disease - A strongly positive Mantoux can support a
clinical diagnosis - Better negative than positive predictive value
- Cut-off for a positive test?
50- Clinical Features
- Sputum Examination
- Chest Radiology
- Bronchoscopy
- Mantoux test
- Indirect laboratory tests
51Indirect Tests
- Biochemical tests
- LDH, Proteins
- Adenosine Deaminase
- Bromide Partition Test
- Gas Chromatography Fatty acids, alcohols etc
- Immuno-diagnosis tests
- Skin test (Mantoux)
- Detection of Antibodies (Tests banned)
- Genetic/ molecular studies
- Antigen detection
- Lipo arabinomannan
- Nucleic Acid Probes
- Ligase Chain Reaction
- Polymerase Chain Reaction
- Gene Xpert
52Serological Tests
- Low turn around time
- Limitation
- Low sensitivity in
- smear negative patients
- HIV positive cases,
- In disease -endemic countries with a
high infection rate - Poor standardization
- Banned in 2012.
53- Interferon-? release assays
- An alternative to the TST in the form of a new
type of in-vitro T-cell-based assay - (Test-tube TST)
- Gold IGRA
- Elispot T test
- T cells of individuals sensitized with
tuberculosis antigens produce interferon-? when
they re-encounter mycobacterial antigens - High level of interferon-? production -
presumptive of tuberculosis infection
54- IGRA in LTBI
- In the absence of a gold standard for diagnosis
of Latent TBI, the sensitivity and specificity
cannot be directly estimated - IGRA have higher specificity than TST
- Better correlation with surrogate markers of
exposure to M tuberculosis (in low-incidence
setting countries) - Less cross reactivity as a result of BCG
vaccination than TST
55- PCR
- Synthesis of dsDNA by hybridization of
oligonucleotides to targets s-DNA - Uses thermal cycler to denature the target DNA
- Thermostable polymerase for DNA amplification
- Repeated cycles by varying temp for primer
annealing (70-72 C) and denaturation (94-96 C) - Amplified product are then detected by southern
blotting and fluorescent/radiolabelled probes
hybridization
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59- Gene X-pert Test
- Detection and identification of
mycobacteriadirectly from clinical samples - Uses real-time polymerase-chain reaction (PCR)
assay to amplify an MTB-specific sequence of the
rpoB gene - Cartridge based, PCR test for detection of
mycobacteria and Rifampicin resistance - Rapid test. Results within hours.
- Costly
- Continuous electric supply and temperature
maintenance - ? Field feasibility, sensitivity and specificity
in India
60- Integrates sample processing and PCR
- Reagents required for bacterial lysis, nucleic
acid extraction, amplification and amplicon
detection are present in a disposable plastic
cartridge - Only manual step -- addition of a bactericidal
buffer to sputum before transferring a defined
volume to the cartridge - MTB/RIF cartridge is then inserted into the
GeneXpert device - Results within 2 hours
61Diagnosis of Extra Pulmonary TB
- Sputum or other smears are often Negative
- These are difficult to use for diagnosis and
start of treatment - Follow up
- Monitoring
- End point
- Recurrence / Relapse
- Mostly clinico-radio-histo/cytological
- Invasive procedures frequently required to obtain
tissue, fluids, etc. to look for T.b. and/or
histo-cytological criteria.
62Difficulties of specimens testing for EPTB
- Specimen
- Relevance of a particular sample
-
- Method of collection
- Contamination/ inappropriate site
- Processing
- Technique, Standardization and calibration of
Instrument/procedure - Clinical interpretation
- Disease ?
63How to confirm the Diagnosis? LEVELS OF
DIAGNOSIS OF TB
- Suggestive
- Clinical/Epidemiological
- Radiological
- Presumptive/Possible
- Therapeutic response
- Immunological
- Markers
- Definitive
- Demonstration of Myco tuberculosis
(smear/ culture) - Histo/Cytological criteria
64EPT DIAGNOSIS
Site Site Empirical/ Suggestive Possible Definitive
1 Lymph Nodes Clinical FNAC (Granuloma) AFB on FNAC
2. Pl. Effusion Clinico-radiological Exudative A.D.A. Pl. biopsy AFB positivity P.C.R.
3. Pericarditis As above As above As above
4. Peritoneal As above As above As above
5. Intestinal Clinical Radiological Biopsy Granuloma AFB positivity
6. Genitourinary Endoscopy As above Biopsy Granuloma AFB positivity
7. Bones Joints Clinical Radiology FNAC Biopsy As above
8. Meningeal As above CSF (Biochem.) CSF PCR AFB
65Comparison of Various Diagnostic Tests for
Diagnosis of TB
Microscopy LED Microscopy GeneXpert MTB/RIF LAMP Solid Culture Liquid Culture
Threshold (CFU/ml) 10,000 - 131 (106-176) - 100 10-50
Turnaround time 1-2 days 1day 90 min - 4-8 week Days - 2 week
Sensitivity 50-60 10 gtthan ZN staining 90 88 Reference Reference
Specificity 98 94 Reference Reference
Technical expertise Required Required Minimal Required Required Required
Biosafety Better than Microscopy
Other Prone to contamination
- Boehme CC et al. Semin Respir Crit Care Med
20133417 31. - Lawn SD et al. Lancet Infect Dis 2013 13 34961.
66- Absence of evidence is not the
evidence of absence - Carl Sagan
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