MBBS Year
2nd Year
Subject
What Is Usually Asked
Morphology, culture, staining, laboratory diagnosis, drug resistance
Resource HubAll Years (1st-Final)Medical Topic AuthorityTuberculosis
Tuberculosis: Notes, PPT and PYQs for MBBS
Tuberculosis (TB) is a chronic granulomatous infectious disease caused by Mycobacterium tuberculosis, most commonly affecting the lungs. Few topics cut across as many MBBS subjects: Microbiology, Pathology and Pharmacology in 2nd Year, Community Medicine in 3rd Year, and General Medicine and Paediatrics in Final Year.
SME-reviewed. Updated 2026.
Open in GeckoMed for PPT slides and notes.Quick Summary: What You Need to Know for University Exams
- Causative agent: Mycobacterium tuberculosis, an acid-fast, aerobic, slow-growing bacillus.
- Spread: Airborne droplet nuclei from people with infectious pulmonary TB.
- Hallmark lesion: Caseating granuloma with epithelioid cells and Langhans giant cells, driven by cell-mediated (Type IV) hypersensitivity.
- Primary TB forms the Ghon focus and Ghon complex; secondary TB typically affects the lung apex and forms cavities.
- Diagnosis in India relies on sputum microscopy and molecular tests such as CBNAAT and Truenat, which also detect rifampicin resistance.
- Treatment of drug-sensitive TB under India's National TB Elimination Programme (NTEP): 2 months of isoniazid, rifampicin, pyrazinamide and ethambutol, then 4 months of isoniazid, rifampicin and ethambutol.
- TB is a notifiable disease in India, and notification is recorded on the Ni-kshay portal.
Tuberculosis Across MBBS Subjects
| MBBS Year | Subject | What Is Usually Asked |
|---|---|---|
| 2nd Year | Microbiology | Morphology, culture, staining, laboratory diagnosis, drug resistance |
| 2nd Year | Pathology | Granuloma, primary and secondary TB, morphology |
| 2nd Year | Pharmacology | First-line antitubercular drugs, adverse effects |
| 3rd Year | Community Medicine | Epidemiology, NTEP, BCG, case definitions, prevention |
| Final Year | General Medicine | Clinical features, diagnosis, management, HIV-TB |
| Final Year | Paediatrics | Childhood TB, TB meningitis, BCG |
MBBS Year
2nd Year
Subject
What Is Usually Asked
Granuloma, primary and secondary TB, morphology
MBBS Year
2nd Year
Subject
What Is Usually Asked
First-line antitubercular drugs, adverse effects
MBBS Year
3rd Year
Subject
What Is Usually Asked
Epidemiology, NTEP, BCG, case definitions, prevention
MBBS Year
Final Year
Subject
What Is Usually Asked
Clinical features, diagnosis, management, HIV-TB
MBBS Year
Final Year
Subject
What Is Usually Asked
Childhood TB, TB meningitis, BCG
Definition and Classification
Definition: Tuberculosis is a chronic infectious disease caused by Mycobacterium tuberculosis complex, characterised pathologically by granuloma formation with caseous necrosis, and most commonly involving the lungs.
Classification:
| Basis | Types |
|---|---|
| Site | Pulmonary TB; extrapulmonary TB (lymph node, pleura, abdomen, bone and spine, meninges, genitourinary tract, pericardium) |
| Stage of infection | Primary TB (first infection); secondary or post-primary TB (reactivation or reinfection) |
| Spread | Localised; disseminated (miliary TB) |
| Diagnostic basis (NTEP) | Microbiologically confirmed; clinically diagnosed |
| Treatment history (NTEP) | New; previously treated |
| Drug susceptibility | Drug-sensitive; drug-resistant |
Basis
Site
Types
Pulmonary TB; extrapulmonary TB (lymph node, pleura, abdomen, bone and spine, meninges, genitourinary tract, pericardium)
Basis
Stage of infection
Types
Primary TB (first infection); secondary or post-primary TB (reactivation or reinfection)
Basis
Spread
Types
Localised; disseminated (miliary TB)
Basis
Diagnostic basis (NTEP)
Types
Microbiologically confirmed; clinically diagnosed
Basis
Treatment history (NTEP)
Types
New; previously treated
Basis
Drug susceptibility
Types
Drug-sensitive; drug-resistant
Aetiology (Causes and Risk Factors)
Causative Organism
- Mycobacterium tuberculosis is the main cause in humans. Other members of the complex include Mycobacterium bovis.
- It is an acid-fast bacillus because of the high mycolic acid content of its cell wall.
- It is aerobic and slow-growing; on Lowenstein-Jensen (LJ) medium it forms rough, buff and tough colonies.
Mode of Transmission
- Inhalation of airborne droplet nuclei released when a person with infectious pulmonary TB coughs, sneezes or speaks.
- Ingestion of unpasteurised milk can transmit M. bovis.
Risk Factors
- HIV infection and other immunosuppression
- Diabetes mellitus
- Undernutrition
- Smoking and alcohol use
- Overcrowding and poor ventilation
- Close contact with a person with infectious TB
- Silicosis
- Long-term corticosteroid or other immunosuppressive therapy
Pathophysiology
Immunopathogenesis: Flowchart
- Inhaled bacilli reach the alveoli and are engulfed by alveolar macrophages
- Bacilli survive and multiply inside macrophages
- Antigen presentation activates CD4+ T helper (Th1) cells
- Th1 cells release interferon-gamma, which activates macrophages
- Activated macrophages become epithelioid cells; some fuse to form Langhans giant cells
- Tumour necrosis factor helps form and maintain the granuloma
- Central caseous necrosis develops within the granuloma
This is a Type IV (delayed-type) hypersensitivity reaction, which is also the basis of the tuberculin skin test.
(Examiner may ask you to draw the pathogenesis flowchart and a labelled tubercle.)
Structure of a Tubercle (Granuloma)
| Zone | Components |
|---|---|
| Centre | Caseous necrosis |
| Surrounding | Epithelioid cells and Langhans giant cells (nuclei arranged in a horseshoe pattern at the periphery) |
| Periphery | Lymphocytes and fibroblasts |
Zone
Centre
Components
Caseous necrosis
Zone
Surrounding
Components
Epithelioid cells and Langhans giant cells (nuclei arranged in a horseshoe pattern at the periphery)
Zone
Periphery
Components
Lymphocytes and fibroblasts
Primary Versus Secondary Tuberculosis
| Feature | Primary TB | Secondary (Post-Primary) TB |
|---|---|---|
| Occurs in | Previously unexposed people, often children | Previously sensitised people |
| Mechanism | First infection | Reactivation of latent infection or reinfection |
| Typical lung site | Subpleural, near the interlobar fissure | Apex of the upper lobe |
| Characteristic lesion | Ghon focus; Ghon complex (Ghon focus plus hilar lymph node involvement) | Cavitation |
| Lymph node involvement | Prominent | Less prominent |
| Usual outcome | Healing by fibrosis and calcification in most | Progressive disease with cavitation and spread if untreated |
Feature
Occurs in
Primary TB
Previously unexposed people, often children
Secondary (Post-Primary) TB
Previously sensitised people
Feature
Mechanism
Primary TB
First infection
Secondary (Post-Primary) TB
Reactivation of latent infection or reinfection
Feature
Typical lung site
Primary TB
Subpleural, near the interlobar fissure
Secondary (Post-Primary) TB
Apex of the upper lobe
Feature
Characteristic lesion
Primary TB
Ghon focus; Ghon complex (Ghon focus plus hilar lymph node involvement)
Secondary (Post-Primary) TB
Cavitation
Feature
Lymph node involvement
Primary TB
Prominent
Secondary (Post-Primary) TB
Less prominent
Feature
Usual outcome
Primary TB
Healing by fibrosis and calcification in most
Secondary (Post-Primary) TB
Progressive disease with cavitation and spread if untreated
Clinical Features
Pulmonary Tuberculosis
- Cough for two weeks or more, with or without sputum
- Haemoptysis
- Fever, typically with an evening rise
- Night sweats
- Loss of weight and appetite
- Chest pain and breathlessness in advanced disease
Extrapulmonary Tuberculosis
| Site | Key Features |
|---|---|
| Lymph node | Most often cervical; matted nodes, cold abscess, sinus formation |
| Pleura | Exudative, lymphocyte-rich pleural effusion |
| Abdomen | Ileocaecal region most commonly involved in the gut; ascites, doughy abdomen, intestinal obstruction |
| Spine (Pott's spine) | Back pain, gibbus deformity, cold abscess, paraplegia |
| Meninges (TB meningitis) | Headache, fever, neck stiffness, cranial nerve palsies, hydrocephalus; more common in children |
| Genitourinary | Sterile pyuria, haematuria, infertility |
| Pericardium | Pericardial effusion, constrictive pericarditis |
| Miliary TB | Haematogenous dissemination; millet-seed shadows on chest X-ray |
Site
Lymph node
Key Features
Most often cervical; matted nodes, cold abscess, sinus formation
Site
Pleura
Key Features
Exudative, lymphocyte-rich pleural effusion
Site
Abdomen
Key Features
Ileocaecal region most commonly involved in the gut; ascites, doughy abdomen, intestinal obstruction
Site
Spine (Pott's spine)
Key Features
Back pain, gibbus deformity, cold abscess, paraplegia
Site
Meninges (TB meningitis)
Key Features
Headache, fever, neck stiffness, cranial nerve palsies, hydrocephalus; more common in children
Site
Genitourinary
Key Features
Sterile pyuria, haematuria, infertility
Site
Pericardium
Key Features
Pericardial effusion, constrictive pericarditis
Site
Miliary TB
Key Features
Haematogenous dissemination; millet-seed shadows on chest X-ray
Diagnosis
| Investigation | Key Points |
|---|---|
| Sputum smear microscopy | Ziehl-Neelsen staining shows red acid-fast bacilli on a blue background; fluorescent (auramine) staining is also used |
| Cartridge-based nucleic acid amplification test (CBNAAT) | Detects M. tuberculosis and rifampicin resistance |
| Truenat | Indigenous chip-based molecular test that detects M. tuberculosis and rifampicin resistance |
| Line probe assay | Detects resistance to isoniazid and rifampicin; second-line assays detect resistance to fluoroquinolones and other drugs |
| Culture and drug susceptibility testing | Solid (LJ medium) or liquid culture; gold standard for confirmation, but slower |
| Chest X-ray | Upper lobe infiltrates, cavities, hilar lymphadenopathy, miliary pattern, pleural effusion |
| Tuberculin skin test (Mantoux) | Indicates infection or prior sensitisation; cannot distinguish active from latent TB |
| Interferon-gamma release assay (IGRA) | Detects TB infection; not affected by prior BCG vaccination |
| Fluid analysis | Pleural or CSF fluid shows a lymphocyte-predominant exudate; raised adenosine deaminase supports TB |
| Fine needle aspiration or biopsy | Shows granulomas with caseous necrosis in lymph node and other tissue TB |
Investigation
Sputum smear microscopy
Key Points
Ziehl-Neelsen staining shows red acid-fast bacilli on a blue background; fluorescent (auramine) staining is also used
Investigation
Cartridge-based nucleic acid amplification test (CBNAAT)
Key Points
Detects M. tuberculosis and rifampicin resistance
Investigation
Truenat
Key Points
Indigenous chip-based molecular test that detects M. tuberculosis and rifampicin resistance
Investigation
Line probe assay
Key Points
Detects resistance to isoniazid and rifampicin; second-line assays detect resistance to fluoroquinolones and other drugs
Investigation
Culture and drug susceptibility testing
Key Points
Solid (LJ medium) or liquid culture; gold standard for confirmation, but slower
Investigation
Chest X-ray
Key Points
Upper lobe infiltrates, cavities, hilar lymphadenopathy, miliary pattern, pleural effusion
Investigation
Tuberculin skin test (Mantoux)
Key Points
Indicates infection or prior sensitisation; cannot distinguish active from latent TB
Investigation
Interferon-gamma release assay (IGRA)
Key Points
Detects TB infection; not affected by prior BCG vaccination
Investigation
Fluid analysis
Key Points
Pleural or CSF fluid shows a lymphocyte-predominant exudate; raised adenosine deaminase supports TB
Investigation
Fine needle aspiration or biopsy
Key Points
Shows granulomas with caseous necrosis in lymph node and other tissue TB
Management
Principles of Treatment
- Use a combination of drugs to prevent drug resistance
- Complete the full course, with an intensive phase followed by a continuation phase
- Ensure adherence with patient support and monitoring
- Test for drug resistance at diagnosis where available
- Manage comorbidities such as HIV and diabetes
Treatment of Drug-Sensitive TB Under NTEP
| Phase | Duration | Drugs |
|---|---|---|
| Intensive phase | 2 months | Isoniazid (H), rifampicin (R), pyrazinamide (Z), ethambutol (E) |
| Continuation phase | 4 months | Isoniazid (H), rifampicin (R), ethambutol (E) |
Phase
Intensive phase
Duration
2 months
Drugs
Isoniazid (H), rifampicin (R), pyrazinamide (Z), ethambutol (E)
Phase
Continuation phase
Duration
4 months
Drugs
Isoniazid (H), rifampicin (R), ethambutol (E)
Drugs are given daily as weight-band based fixed-dose combinations. The continuation phase may be extended in certain forms of extrapulmonary TB, such as TB of the central nervous system or bones and joints, as per national guidelines.
First-Line Antitubercular Drugs
| Drug | Mechanism of Action | Key Adverse Effects |
|---|---|---|
| Isoniazid | Inhibits mycolic acid synthesis | Hepatitis, peripheral neuropathy (prevented with pyridoxine) |
| Rifampicin | Inhibits bacterial DNA-dependent RNA polymerase | Hepatitis, orange-red discolouration of body fluids, liver enzyme induction and drug interactions |
| Pyrazinamide | Active against bacilli in an acidic intracellular environment | Hepatotoxicity, hyperuricaemia and joint pain |
| Ethambutol | Inhibits arabinosyl transferase, affecting cell wall synthesis | Optic neuritis with reduced visual acuity and red-green colour blindness |
Drug
Isoniazid
Mechanism of Action
Inhibits mycolic acid synthesis
Key Adverse Effects
Hepatitis, peripheral neuropathy (prevented with pyridoxine)
Drug
Rifampicin
Mechanism of Action
Inhibits bacterial DNA-dependent RNA polymerase
Key Adverse Effects
Hepatitis, orange-red discolouration of body fluids, liver enzyme induction and drug interactions
Drug
Pyrazinamide
Mechanism of Action
Active against bacilli in an acidic intracellular environment
Key Adverse Effects
Hepatotoxicity, hyperuricaemia and joint pain
Drug
Ethambutol
Mechanism of Action
Inhibits arabinosyl transferase, affecting cell wall synthesis
Key Adverse Effects
Optic neuritis with reduced visual acuity and red-green colour blindness
For drug groups and revision, see the antibiotic classification chart.
Drug-Resistant Tuberculosis: Definitions
| Term | Definition |
|---|---|
| Rifampicin-resistant TB (RR-TB) | Resistance to rifampicin |
| Multidrug-resistant TB (MDR-TB) | Resistance to at least isoniazid and rifampicin |
| Pre-extensively drug-resistant TB (pre-XDR-TB) | MDR/RR-TB with resistance to a fluoroquinolone |
| Extensively drug-resistant TB (XDR-TB) | MDR/RR-TB with resistance to a fluoroquinolone and at least one of bedaquiline or linezolid |
Term
Rifampicin-resistant TB (RR-TB)
Definition
Resistance to rifampicin
Term
Multidrug-resistant TB (MDR-TB)
Definition
Resistance to at least isoniazid and rifampicin
Term
Pre-extensively drug-resistant TB (pre-XDR-TB)
Definition
MDR/RR-TB with resistance to a fluoroquinolone
Term
Extensively drug-resistant TB (XDR-TB)
Definition
MDR/RR-TB with resistance to a fluoroquinolone and at least one of bedaquiline or linezolid
Drug-resistant TB is treated with specialised regimens under NTEP guidelines. At MBBS level, focus on definitions, causes of resistance (irregular or incomplete treatment) and prevention.
TB and HIV
- TB is a common opportunistic infection in people living with HIV.
- Both infections are treated together, with timing of antiretroviral therapy guided by national guidelines.
- Immune reconstitution inflammatory syndrome (IRIS) can occur after starting antiretroviral therapy.
Prevention and Control (Community Medicine Angle)
| Measure | Key Points |
|---|---|
| BCG vaccination | Live attenuated vaccine given at birth under India's national immunisation schedule; protects against severe childhood forms such as TB meningitis and miliary TB |
| Early case finding | Screening people with presumptive TB symptoms and high-risk groups |
| Notification | TB is notifiable in India; cases are recorded on the Ni-kshay portal |
| Complete treatment | Supports cure and prevents drug resistance |
| TB preventive treatment | Offered to eligible contacts and high-risk groups as per national guidelines |
| Nutritional support | Provided to TB patients under the Ni-kshay Poshan Yojana through direct benefit transfer |
| Infection control | Cough etiquette, ventilation and reducing overcrowding |
Measure
BCG vaccination
Key Points
Live attenuated vaccine given at birth under India's national immunisation schedule; protects against severe childhood forms such as TB meningitis and miliary TB
Measure
Early case finding
Key Points
Screening people with presumptive TB symptoms and high-risk groups
Measure
Notification
Key Points
TB is notifiable in India; cases are recorded on the Ni-kshay portal
Measure
Complete treatment
Key Points
Supports cure and prevents drug resistance
Measure
TB preventive treatment
Key Points
Offered to eligible contacts and high-risk groups as per national guidelines
Measure
Nutritional support
Key Points
Provided to TB patients under the Ni-kshay Poshan Yojana through direct benefit transfer
Measure
Infection control
Key Points
Cough etiquette, ventilation and reducing overcrowding
National programme: India's TB control programme was renamed the National TB Elimination Programme (NTEP) in 2020. India set a goal of ending TB by 2025, five years ahead of the Sustainable Development Goal target of 2030.
See the national immunisation schedule for India for BCG timing.
Complications
Pulmonary:
- Massive haemoptysis
- Pneumothorax
- Bronchiectasis
- Aspergilloma in an old cavity
- Pulmonary fibrosis and cor pulmonale
- Empyema
- Respiratory failure
Systemic and treatment-related:
- Secondary (reactive) amyloidosis
- Spread to other organs, including miliary TB
- Drug-induced hepatitis and other adverse drug reactions
- Development of drug resistance with incomplete treatment
Prognosis
Drug-sensitive TB is curable when the full course of treatment is completed. Poor adherence, HIV co-infection, undernutrition, diabetes and drug resistance are associated with poorer outcomes, relapse and death.
How Tuberculosis Appears in MBBS University Exams
TB is asked across subjects. Typical question styles (not attributed to specific papers or years):
- "Describe the pathogenesis and morphology of pulmonary tuberculosis. Add a note on primary complex." (Long essay, Pathology)
- "Describe the laboratory diagnosis of pulmonary tuberculosis." (Long essay, Microbiology)
- "Classify antitubercular drugs. Write the mechanism of action and adverse effects of isoniazid and rifampicin." (Pharmacology)
- "Write a short note on multidrug-resistant tuberculosis." (Short note, Medicine or Microbiology)
- "Describe the National TB Elimination Programme." (Long essay, Community Medicine)
- "Write a short note on BCG vaccine." (Short note, Community Medicine or Paediatrics)
- "Write a short note on tuberculous meningitis." (Short note, Medicine or Paediatrics)
Frequently Asked Questions
What is the treatment of drug-sensitive TB under NTEP?
A 2-month intensive phase of isoniazid, rifampicin, pyrazinamide and ethambutol, followed by a 4-month continuation phase of isoniazid, rifampicin and ethambutol, given daily as weight-band based fixed-dose combinations.
What is the difference between the Ghon focus and the Ghon complex?
The Ghon focus is the initial subpleural lung lesion of primary TB. The Ghon complex is the Ghon focus together with involvement of the draining hilar lymph nodes.
Can I download the tuberculosis PPT for my presentation?
Yes. Use the Download PPT button at the top of this page. The GeckoMed app also gives offline access to the slides and notes.
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