PULMONARY TUBERCULOSIS

✓ Medically ReviewedDISEASEID: MDBT0199🚨 TRIAGE: URGENTICD-10: A15.0

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Definition

CLINICAL DEFINITION

An infectious disease of the lung parenchyma caused by the Mycobacterium tuberculosis complex, characterised by granulomatous inflammation, caseating necrosis, and cavitation, typically presenting with chronic cough, haemoptysis, fever, night sweats, and weight loss.

IN PLAIN ENGLISH

A serious bacterial infection that mainly affects the lungs, causing a persistent cough, fever, and weight loss. It spreads through the air when an infected person coughs or sneezes.

COMMON MISCONCEPTION / WHAT IT DOES NOT MEAN

Pulmonary Tuberculosis is NOT simply any chronic cough or lung infection; it specifically requires identification of the Mycobacterium tuberculosis complex or compatible histopathology. It is also distinct from non-tuberculous mycobacterial (NTM) lung disease, which does not typically spread person-to-person and has different treatment protocols.

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Word Breakdown

pulmo-

=relating to the lungs (from Latin 'pulmo')

tubercul-

=small swelling or nodule (from Latin 'tuberculum')

-osis

=condition, disease, or increase (from Greek '-osis')

Literal Meaning: A condition of the lungs characterised by small nodules (tubercles)

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Abbreviations

PTB=Pulmonary Tuberculosis — standard clinical abbreviation for TB affecting the lungs

AFB=Acid-Fast Bacilli — refers to the mycobacteria seen on sputum smear microscopy

MDR-TB=Multidrug-Resistant Tuberculosis — TB resistant to at least isoniazid and rifampicin

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Synonyms & Variants

Consumption›Phthisis›Pulmonary TB›

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Category-Specific Context

As a Disease, pulmonary tuberculosis represents a specific infectious pathology with defined microbiological and histological criteria. It is classified based on drug susceptibility (drug-susceptible vs. multidrug-resistant), anatomical site (pulmonary vs. extrapulmonary), and bacteriological confirmation status.

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Clinical Context & Usage

CLINICAL SETTINGS

Respiratory Medicine ClinicInfectious Disease WardEmergency DepartmentPublic Health Tuberculosis ClinicGeneral PracticeIntensive Care Unit

USAGE & DOCUMENTATION NOTES

Often documented as 'PTB' or simply 'TB' in clinical notes. Clinicians frequently refer to 'smear-positive' or 'smear-negative' PTB based on initial sputum microscopy results, and 'culture-confirmed' once mycobacterial cultures yield M. tuberculosis. Treatment regimens are often abbreviated, e.g., '2HRZE/4HR' denoting the intensive and continuation phases.

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Primary Causes & Pathophysiology

PATHOPHYSIOLOGY

Infection begins with the inhalation of aerosolised droplet nuclei containing Mycobacterium tuberculosis into the alveoli. Alveolar macrophages phagocytose the bacilli, but the bacteria evade intracellular killing by inhibiting phagolysosome fusion, allowing them to replicate. This triggers a cell-mediated immune response, leading to the recruitment of monocytes and lymphocytes, which form a granuloma (tubercle) to contain the infection. The centre of the granuloma often undergoes caseous necrosis. In primary infection, the bacteria may remain dormant (latent TB) or progress to active disease. Reactivation or progressive primary disease leads to liquefaction of caseous material, cavity formation, and endobronchial spread, resulting in the classic clinical manifestations of pulmonary TB and enabling airborne transmission.

PRIMARY CAUSES

Mycobacterium tuberculosis

The primary aetiological agent; an aerobic, acid-fast bacillus that survives within macrophages and causes caseating granulomatous inflammation in the lung parenchyma.

Mycobacterium bovis

A member of the MTB complex historically transmitted via unpasteurised milk; can cause pulmonary disease, though less common than M. tuberculosis in most regions today.

Mycobacterium africanum

A member of the MTB complex primarily found in West Africa, causing a clinical syndrome indistinguishable from M. tuberculosis pulmonary disease.

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Drug-Induced Causes

💊 Tumour Necrosis Factor (TNF) alpha inhibitors (e.g., infliximab, adalimumab) ↗

Mechanism: TNF-alpha is essential for granuloma formation and maintenance; its inhibition disrupts granuloma integrity, leading to reactivation of latent tuberculosis.

→ Screen all patients for latent TB (IGRA or TST) before initiating therapy; treat latent TB if positive before starting the biologic.

💊 Corticosteroids (prolonged high-dose) ↗

Mechanism: Suppress cell-mediated immunity, increasing the risk of reactivation of latent TB or progression of primary infection.

→ Consider latent TB screening in high-risk populations prior to prolonged use; monitor closely for TB symptoms during treatment.

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Epidemiology

Prevalence:Globally, an estimated 10.8 million people fell ill with TB in 2023, with pulmonary TB accounting for the majority of cases. Incidence varies drastically by region, with the highest burdens in South-East Asia, Africa, and the Western Pacific.

Age Group:Can affect all age groups. Highest incidence of active pulmonary disease is often seen in young adults (15–45 years) in high-burden countries, while in low-burden countries, it disproportionately affects older adults due to reactivation of latent infection acquired decades earlier.

Sex Predilection:Male

Geographic Distribution:Highly concentrated in low- and middle-income countries. Over 80% of global cases occur in 30 high TB burden countries, with India, Indonesia, China, the Philippines, and Pakistan accounting for more than half of all cases.

Red Flags & Triage ★

TRIAGE LEVEL

🚨 URGENT

DO NOT MISS — LIFE-THREATENING PRESENTATIONS

Concomitant HIV infection — all patients diagnosed with TB must be tested for HIV, as co-infection drastically alters prognosis, increases transmission risk, and requires careful timing of antiretroviral therapy to avoid Immune Reconstitution Inflammatory Syndrome (IRIS).
Drug-resistant TB — failure to identify rifampicin resistance early (e.g., via Xpert MTB/RIF) leads to inappropriate standard therapy, treatment failure, and amplification of resistance; always check drug susceptibility results before assuming standard regimen efficacy.

URGENT EVALUATION TRIGGERS

Massive haemoptysis (>600 mL in 24 hours or causing haemodynamic instability) — requires immediate airway protection, resuscitation, and likely bronchial artery embolisation or surgery.
Spontaneous pneumothorax — a known complication of ruptured cavitary TB, presenting with sudden pleuritic chest pain and acute dyspnoea.
Altered mental status or severe headache in a TB patient — raises concern for tuberculous meningitis, a life-threatening extrapulmonary complication requiring immediate lumbar puncture and CNS-penetrating therapy.

Contraindications & Precautions

SPECIAL PRECAUTIONS

Airborne infection isolation — patients with suspected or confirmed smear-positive pulmonary TB must be placed in a negative-pressure room
and healthcare workers must wear fit-tested N95/FFP2 respirators.
Directly Observed Therapy (DOT) — adherence to the prolonged multi-drug regimen must be supported and monitored to prevent the emergence of drug resistance.
Hepatotoxicity monitoring — first-line drugs (isoniazid
rifampicin
pyrazinamide) can cause drug-induced liver injury; baseline and periodic LFTs are required
especially in older adults or those with pre-existing liver disease.

Complications

DOWNSTREAM CLINICAL COMPLICATIONS

Haemoptysis and massive pulmonary haemorrhage — erosion of pulmonary vessels (e.g.
Rasmussen's aneurysm) within a cavity.
Bronchiectasis — permanent airway dilation due to chronic inflammation and structural lung damage.
Aspergilloma (mycetoma) — colonisation of a healed TB cavity by Aspergillus fumigatus.
Respiratory failure and chronic cor pulmonale — from extensive parenchymal destruction and pulmonary hypertension.
Miliary tuberculosis — haematogenous dissemination leading to widespread organ involvement.

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Confused With (LASA & DDx) ★

LEXICAL (LASA) — SIMILAR NAMES

Non-tuberculous Mycobacteria (NTM)

Can cause similar cavitary lung disease and positive acid-fast smears, but NTM does not require public health notification and has different treatment regimens.

Lung Cancer

Can present with chronic cough, haemoptysis, and weight loss; cavitating squamous cell carcinoma can mimic a TB cavity on imaging.

CLINICAL DIFFERENTIAL DIAGNOSES (DDx)

Lung Malignancy

Key Distinguishing Feature: Often presents in older smokers; imaging may show a spiculated mass rather than apical cavitation; diagnosis confirmed by biopsy/cytology, not AFB smear.

Non-tuberculous Mycobacterial (NTM) Infection

Key Distinguishing Feature: More common in patients with underlying structural lung disease (e.g., bronchiectasis); does not typically transmit human-to-human; requires specific species identification for treatment.

Sarcoidosis

Key Distinguishing Feature: Typically presents with bilateral hilar lymphadenopathy and non-caseating granulomas on biopsy; ACE levels may be elevated; negative AFB smears and cultures.

Chronic Pulmonary Aspergillosis

Key Distinguishing Feature: Often occurs in patients with prior structural lung damage (including prior TB); Aspergillus IgG positive; fungal elements seen on microscopy.

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Clinical Pearls

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The classic triad of fever, night sweats, and weight loss is highly suggestive but not universally present; many patients, particularly the elderly or immunocompromised, may present with atypical or indolent symptoms.

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A negative sputum AFB smear does not rule out pulmonary TB. Smear-negative TB is common, especially in HIV-coinfected patients, and requires a high index of suspicion, reliance on NAAT (like Xpert MTB/RIF), culture, and radiological correlation.

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Rifampicin is a potent inducer of the cytochrome P450 system. It significantly reduces the efficacy of many medications, including oral contraceptives, warfarin, and antiretrovirals; a thorough medication reconciliation is mandatory before starting TB therapy.

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Apical cavitary disease is the hallmark of reactivation TB in immunocompetent adults, whereas primary TB or TB in severely immunocompromised patients (e.g., advanced HIV) often presents with lower zone consolidation, miliary patterns, or prominent intrathoracic lymphadenopathy without cavitation.

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Example Usage & SOAP

CLINICAL SENTENCE

"The patient is a 34-year-old male presenting with a 6-week history of productive cough, night sweats, and a 5 kg weight loss; chest X-ray reveals a right upper lobe cavity, and sputum AFB smear is 3+, highly suggestive of active pulmonary tuberculosis."

IN A SOAP NOTE

S: 45-year-old female immigrant from a high TB burden country presents with a 4-week history of chronic cough, occasional blood-streaked sputum, drenching night sweats, and unintentional weight loss of 4 kg. O: Vitals: T 38.1°C, HR 98, RR 18, SpO2 96% on room air. BMI 18.5. Chest exam reveals decreased breath sounds and coarse crackles in the right upper zone. CXR shows a 3 cm cavitary lesion in the right apical segment with surrounding consolidation. A: High clinical suspicion for active pulmonary tuberculosis given the demographic risk factors, classic constitutional symptoms, and cavitary lung lesion. P: Place patient in airborne infection isolation room. Obtain 3 early morning sputum samples for AFB smear, mycobacterial culture, and Xpert MTB/RIF. Send baseline LFTs, U&Es, HIV test, and Hepatitis B/C serology. Notify public health authorities.

DIFFERENTIAL DIAGNOSIS CONTEXT

Differential for a cavitary lung lesion with chronic cough: (1) Reactivation Pulmonary Tuberculosis — typically apical, positive AFB/NAAT, constitutional symptoms; (2) Lung Malignancy (e.g., squamous cell carcinoma) — usually older smokers, thick-walled irregular cavity, malignant cells on biopsy; (3) Lung Abscess (anaerobic/bacterial) — often history of aspiration, air-fluid level on imaging, responds to standard antibiotics; (4) Chronic Pulmonary Aspergillosis — usually underlying structural lung disease, positive Aspergillus IgG.

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Prognosis

SHORT-TERM OUTCOME

With appropriate, fully susceptible multi-drug therapy, sputum cultures typically convert to negative within 2 months, and clinical symptoms (cough, fever) improve significantly within 2–4 weeks.

LONG-TERM PROGNOSIS

Drug-susceptible pulmonary TB has a cure rate exceeding 85–90% with standard 6-month regimens. However, survivors of severe cavitary disease may have permanent structural lung damage (post-TB lung disease) leading to chronic respiratory impairment. MDR-TB requires longer, more toxic regimens with lower success rates.

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References & Coding

ICD-10 DIAGNOSTIC CODE

A15.0

LITERATURE CITATIONS & GUIDELINES

[1]Nahid P et al. Official American Thoracic Society/Centers for Disease Control and Prevention/Infectious Diseases Society of America Clinical Practice Guidelines: Treatment of Drug-Susceptible Tuberculosis. Clin Infect Dis. 2016;63(7):e147-e195.

[2]WHO. WHO consolidated guidelines on tuberculosis: module 4: treatment - drug-resistant tuberculosis treatment. 2022.

[3]NICE. Tuberculosis. NICE guideline [NG33]. 2016.

MEDICAL DISCLAIMER — This content is intended for educational purposes and qualified healthcare professionals only. Always refer to current clinical diagnostic criteria, institutional protocols, and official guidelines. Medobo is not responsible for clinical decisions made based on this content.