Tuberculosis

Tuberculosis (TB) is a chronic, subacute, or acute communicable granulomatous infectious disease caused by acid-fast bacilli belonging to the Mycobacterium tuberculosis complex. Although the disease primarily targets the respiratory system (Pulmonary Tuberculosis - PTB), hematogenous and lymphatic dissemination can infect virtually any vascularized anatomical organ or tissue structure in the human body (Extra-Pulmonary Tuberculosis - EPTB).

• Taxonomy: Member of the Mycobacteriaceae family within the Mycobacterium tuberculosis complex (which includes M. tuberculosis, M. bovis, M. africanum, M. microti, and M. canettii). M. tuberculosis (MTB) is responsible for the vast majority of human disease.
• Cellular Morphology & Physiology: MTB is a slender, slightly curved or straight, non-motile, non-spore-forming, obligate aerobic rod-shaped bacillus measuring 0.5 μm in width and 2 to 4 μm in length. As an obligate aerobe, it thrives in tissues with high oxygen tension, explaining its pronounced predilection for the apical and posterior segments of the upper pulmonary lobes.
• The Unique Mycobacterial Cell Envelope: The cell wall architecture is exceptionally thick, hydrophobic, waxy, and rich in complex lipids (accounting for up to 60% of the total dry wall weight). Key structural components include:
  • Mycolic Acids: Long-chain β-hydroxy fatty acids that form a dense, lipid-shell barrier rendering the organism impervious to Gram staining, drying, osmotic lysis, chemical disinfectants, acids, alkalis, and many conventional antibacterial agents.
  • Arabinogalactan & Peptidoglycan: Provide covalent structural rigidity and anchor the outer mycolate layer to the inner plasma membrane.
  • Lipoarabinomannan (LAM): A surface lipoglycan functionally analogous to endotoxin; it inhibits macrophage activation, scavenges cytotoxic oxygen free radicals, suppresses T-cell proliferation, and blocks host phagosome-lysosome fusion.
  • Cord Factor (Trehalose 6,6'-dimycolate): Causes virulent bacilli to align in parallel serpentine microscopic cords; it induces chronic granuloma formation, inhibits leukocyte migration, and disrupts host mitochondrial respiration.
• Acid-Fastness: Once stained with heated phenolic carbolfuchsin (Ziehl-Neelsen or Kinyoun method), the dye forms a stable complex with mycolic acids that resists destaining with strong mineral acids and ethanol (3% hydrochloric acid in 95% ethanol). Hence, they are defined as Acid-Alcohol Fast Bacilli (AAFB). Under fluorescent microscopy, they retain fluorochrome dyes (Auramine-O and Rhodamine).
• Slow Growth Rate: MTB possesses an extraordinarily prolonged generation time of 15 to 20 hours. Consequently, visible colonies typically require 2 to 6 weeks of incubation on solid egg-based media (Lowenstein-Jensen) and 1 to 3 weeks in automated liquid culture systems (Bactec MGIT).

• Airborne Droplet Nuclei: Transmission occurs via inhalation of microscopic airborne droplet nuclei (measuring 1 to 5 μm in diameter) generated when an individual with active, untreated cavitary pulmonary or laryngeal TB coughs, sneezes, shouts, or sings. A single forceful cough produces up to 3,000 droplet nuclei, each containing 1 to 3 viable bacilli.
• Environmental Persistence: Due to their tiny mass, droplet nuclei remain buoyantly suspended in ambient air currents for hours in enclosed, poorly ventilated spaces.
• Ingestion Route: Ingestion of unpasteurized cow's milk contaminated with Mycobacterium bovis penetrates intestinal Peyer's patches, producing primary gastrointestinal and mesenteric lymph node tuberculosis (zoonotic TB).
• Non-Transmissibility: TB is not transmitted through fomites, clothing, bedding, sharing eating utensils, or casual physical touch. Extrapulmonary TB (without concomitant pulmonary involvement) is non-infectious to others.

1. Inhalation & Alveolar Implantation: Droplet nuclei bypass the mucociliary escalator of the upper airways and settle in the peripheral subpleural alveoli, typically in the mid-to-lower pulmonary zones.
2. Phagocytosis & Intracellular Parasitism: Resting alveolar macrophages phagocytose the bacilli via complement (CR3) and mannose receptors. MTB evades destruction by secreting protein kinase G and the cell wall lipid sulfatide, which prevent the fusion of phagosomes with lysosomes and inhibit phagosomal acidification (maintaining pH > 6.4). The bacilli replicate unhindered within the macrophage cytosol.
3. Lysis & Early Hematogenous Seeding: Macrophages rupture, releasing bacilli that recruit fresh blood monocytes. Bacilli drain via pulmonary lymphatics to the bronchopulmonary and hilar lymph nodes. A low-grade, clinically silent bacteremia disseminates bacilli throughout the vascular tree, seeding the apices of the lungs, renal cortices, vertebral bodies, meninges, and epiphyses of long bones (forming dormant metastatic foci).
4. Cell-Mediated Immunity (CMI) & Delayed Hypersensitivity: Between 2 to 8 weeks post-infection, dendritic cells transport mycobacterial antigens to regional lymph nodes, priming CD4+ T-helper 1 (Th1) cells. Activated Th1 cells secrete Interferon-gamma (IFN-γ) and Interleukin-2 (IL-2). IFN-γ potently activates naive macrophages, upregulating inducible nitric oxide synthase (iNOS), generating reactive nitrogen intermediates , hydrogen peroxide, and lysosomal enzymes capable of destroying intracellular bacilli.
5. The Tuberculous Granuloma: Activated macrophages transform into large epithelioid histiocytes with abundant pink cytoplasm and interdigitating cell membranes. These fuse together under the influence of IFN-γ to form multinucleated Langhans giant cells (nuclei arranged in a peripheral horseshoe pattern). The lesion is enclosed by a dense cuff of CD4+ and CD8+ T-lymphocytes, B-cells, and an outer rim of fibroblasts depositing collagen.
6. Ghon Focus, Ghon Complex, and Ranke Complex:
   • Ghon Focus: The localized primary parenchymal subpleural granuloma in the mid/lower lung field.
   • Ghon (Primary) Complex: The anatomical combination of the Ghon focus, draining inflamed lymphatics (lymphangitis), and enlarged caseous regional hilar/mediastinal lymph nodes.
   • Ranke Complex: The late, burnt-out, fibrocalcified radiological remnant of the Ghon complex.

• Latent TB Infection (LTBI): In approximately 90% of immunocompetent individuals, the cell-mediated immune response arrests bacillary proliferation. Granulomas undergo peripheral fibrosis, hyalinization, and dystrophic calcification. Viable bacilli enter a dormant, non-replicating metabolic state (persisters) inside caseous cores for the lifetime of the host. Individuals with LTBI have no clinical signs or symptoms, cannot transmit the organism, have normal chest radiographs, but test positive on Tuberculin Skin Tests (TST) or Interferon-Gamma Release Assays (IGRA).
• Post-Primary (Secondary / Reactivation) Tuberculosis: Occurs when host cell-mediated immunity declines (due to HIV infection, malnutrition, aging, diabetes mellitus, end-stage renal disease, anti-TNF-α biologics, or systemic corticosteroids), allowing dormant bacilli within old apical seeding sites (Simon foci) to resume active multiplication. Less commonly, it occurs via exogenous reinfection.
• Caseation, Liquefaction, and Cavitation:
  • The sensitized host mounts a massive delayed-type hypersensitivity reaction, releasing high levels of Tumor Necrosis Factor-alpha (TNF-α), leading to avascular coagulative tissue necrosis characterized by soft, friable, debris resembling clotted cheese (caseous necrosis).
  • Hydrolytic enzymes released by dying macrophages digest protein matrices, transforming solid caseum into liquid material (liquefaction).
  • The liquefied necrotic mass erodes through the wall of an adjacent bronchial branch and discharges into the bronchial tree, leaving behind an empty, air-filled, rigid cavity (cavitation).
  • Bacteriological Explosion: Cavity walls provide an open, oxygen-saturated, hyper-vascular environment that fuels uncontrolled extracellular bacterial replication, generating up to $$10^7$$ to $$10^9$$ bacilli per cavity. Coughing expels enormous loads of infectious droplet nuclei into the air.
• Rasmussen Aneurysm: Progressive granulomatous necrotizing inflammation of a cavity wall erodes and thins the adventitia and media of an adjacent branch of the pulmonary artery. The weakened vascular wall dilates into a pseudoaneurysm. Rupture of a Rasmussen aneurysm produces sudden, cataclysmic, fatal arterial massive hemoptysis.

PTB has an insidious onset, frequently progressing over weeks to months prior to clinical presentation:

• Persistent Chronic Cough: Typically productive of mucoid or mucopurulent sputum lasting ≥ 2 weeks (any duration in HIV-infected patients). Cough may initially be dry and hacking.
• Hemoptysis: Ranging from blood-streaked sputum to life-threatening frank hemorrhage (due to cavitary erosion or Rasmussen aneurysm rupture).
• Low-Grade Afternoon / Evening Fever: Diurnal temperature elevation characteristically spiking between 37.8°C and 39.0°C in the late afternoon or evening, subsiding by morning.
• Drenching Night Sweats: Severe nocturnal diaphoresis requiring the patient to change clothes and bedsheets, occurring as the evening fever lysis.
• Significant Unintentional Weight Loss ("Consumption"): Progressive wasting of somatic fat and skeletal muscle mass driven by high levels of circulating TNF-α (cachectin) and catabolic cytokines.
• Anorexia & Profound Asthenia: Loss of appetite and debilitating physical lethargy.
• Pleuritic Chest Pain: Sharp, stabbing, localized pain exacerbated by deep inspiration and coughing, indicating subpleural inflammation or parietal pleural extension.
• Dyspnea: Exertional breathlessness developing in extensive parenchymal destruction, spontaneous secondary pneumothorax, large tuberculous pleural effusion, or end-stage fibrocavitary disease.

• General Inspection: Cachexia, temporal wasting, marked pallor of the conjunctivae, digital clubbing (in chronic advanced disease).
• Chest Palpation & Percussion: Dullness to percussion over areas of dense lobar consolidation, fibro-atelectasis, or pleural effusion. Hyperresonance if a tension pneumothorax complicates cavitary rupture. Asymmetrical chest expansion.
• Auscultation: Bronchial breath sounds and aegophony over consolidations; coarse post-tussive apical crackles (amphoric breathing over large empty cavities); absent or diminished breath sounds at the base in pleural effusion.

EPTB accounts for 15% to 25% of all TB cases in immunocompetent hosts, and upwards of 50% in individuals co-infected with HIV. It arises from early hematogenous or lymphatic seeding during primary infection or late reactivation.

The single most frequent clinical manifestation of EPTB globally, accounting for 35% of extrapulmonary cases.

• Anatomical Distribution: Primarily targets the anterior and posterior cervical lymph nodes along the sternocleidomastoid muscle, followed by supraclavicular, submandibular, and axillary chains. Usually unilateral.
• Natural Progression (The 5 Stages of Jones & Campbell):
  • Stage 1: Firm, discrete, movable, painless, non-tender enlarged nodes without peri-adenitis.
  • Stage 2: Large rubbery nodes becoming fixed to each other and surrounding subcutaneous tissues due to peri-adenitis (matted lymph nodes).
  • Stage 3: Central caseous liquefaction and necrosis producing a soft, fluctuant mass ("cold abscess").
  • Stage 4: The cold abscess erodes through deep cervical fascia; the skin becomes violaceous, thin, and adheres to the mass (collar-stud abscess).
  • Stage 5: Spontaneous rupture through the skin surface forming an indolent, chronic tuberculous sinus tract that discharges pale, thick caseous material and heals with hypertrophic, puckered scarring.
• Diagnosis: Fine-Needle Aspiration Biopsy (FNAB) evaluated with GeneXpert MTB/RIF, AFB staining, and cytology (epithelioid histiocytes, Langhans giant cells, and background caseous necrosis).

• Pathogenesis: Rupture of an immediate subpleural caseous focus into the pleural space introduces mycobacterial proteins, triggering an acute delayed hypersensitivity immune reaction with intense capillary permeability.
• Clinical Features: Acute or subacute onset of dry cough, high fever, and severe unilateral pleuritic chest pain. As the pleural fluid accumulates, pleuritic pain resolves, replaced by progressive dyspnea.
• Diagnostic Pleural Fluid Tap (Thoracentesis):
  • Macroscopic Appearance: Serous, straw-colored, clear or turbid fluid (pus indicates tuberculous empyema).
  • Exudative Criteria (Light’s Criteria): Pleural fluid to serum total protein ratio > 0.5; pleural fluid to serum LDH ratio > 0.6.
  • Cytology: Predominantly marked lymphocytic pleocytosis (often >80% small, mature lymphocytes); absence of mesothelial cells (<5%).
  • Biochemical Markers: Adenosine Deaminase (ADA) > 40 U/L and elevated Interferon-gamma levels are highly sensitive and specific for TB pleurisy.
  • Bacteriology: Direct smear AFB positivity is low (<10%), but GeneXpert and pleural biopsy with an Abram's needle yield granulomas in >80% of cases.

Musculoskeletal TB accounts for approximately 10% of EPTB cases, and the vertebral spine is involved in 50% of these cases. It is the most clinically destructive form of skeletal tuberculosis.

1. Vascular Seeding: Bacilli seed the vertebral column via the arterial arcades of the anterior spinal artery or retrograde flow through the valveless Batson’s paravertebral venous plexus from the pelvis or abdomen.
2. Site Predilection: The anterior inferior and superior margins of the vertebral bodies adjacent to the intervertebral disc are most vascularized; hence, the paradiscal region of the lower thoracic (T8–T12) and upper lumbar (L1–L3) spine is the most frequent primary site.
3. Disc Infiltration & Destruction: Unlike pyogenic bacterial spondylodiscitis (where proteolytic enzymes rapidly liquefy the intervertebral disc early), MTB lacks collagenolytic enzymes. In Pott's disease, the disc initially survives but is secondarily starved of nutrients as the subchondral bone plates are destroyed by caseous osteomyelitis. Infection spreads beneath the anterior longitudinal ligament to involve adjacent contiguous vertebral bodies.
4. Vertebral Collapse & Kyphosis: Avascular necrosis destroys the anterior portion of the vertebral bodies while the strong posterior vertebral elements (pedicles, laminae, spinous processes) are relatively spared. Axial gravity causes wedging and structural collapse of the anterior column, producing a sharp, acute backward posterior angulation known as an angular Gibbus deformity (kyphosis).
5. Cold Abscess Formation: Liquefied caseous necrotic pus tracks along tissue planes and fascial sheaths without classical heat or erythema:
   • Cervical Spine: Forms a retropharyngeal abscess (causing dysphagia, stridor, and respiratory distress) or tracks along the scalene fascia into the posterior triangle of the neck.
   • Thoracic Spine: Expands fusiformly along the anterior longitudinal ligament, producing a characteristic bilateral "bird's nest" or paravertebral spindle shadow on plain AP radiographs.
   • Lumbar Spine: Enters the psoas muscle sheath, forming a massive Psoas Abscess that tracks downward beneath the inguinal ligament to present as a painless, fluctuant swelling in the femoral triangle, groin, or gluteal region.

• Localized, dull, deep-seated aching back pain and stiffness; characteristically aggravated by movement and weight-bearing, relieved by recumbency.
• "Night Cries" in children: Muscle spasms relax during deep sleep, permitting diseased bone ends to rub against each other, awakening the child screaming with pain.
• Palpable spinous process tenderness and visible angular kyphotic step-off (gibbus).
• Pott's Paraplegia (Neurological Deficits): Motor weakness, spasticity, hyperreflexia, positive Babinski reflex, ankle clonus, sensory level deficits, and bladder/bowel incontinence caused by spinal cord compression from:
  • Early-onset paraplegia (Active Disease): Extradural mechanical compression by inflammatory cold abscess, granulation tissue, caseous debris, or sequestrated necrotic disc fragments. (High reversibility with chemotherapy).
  • Late-onset paraplegia (Healed Disease): Permanent mechanical cord transection over a sharp, calcified internal bony ridge at the apex of severe kyphotic deformity or pachymeningitis. (Poor neurological prognosis).

• Medical Chemotherapy: Extended-duration antitubercular therapy is the primary treatment: 2 months 2RHZE followed by 7 to 10 months of 4RH (Total duration: 9 to 12 months).
• Conservative Immobilization: Strict bed rest during the acute painful phase on a firm mattress, followed by rigid external spinal orthosis (Taylor brace, molded thoraco-lumbar-sacral orthosis [TLSO], or Minerva cast).
• Absolute Indications for Surgical Decompression & Spinal Fusion:
  • Development or progression of neurological deficits (Pott's paraplegia) despite active chemotherapy.
  • Severe mechanical spinal instability or pan-vertebral destruction.
  • Severe kyphotic deformity (>40–60 degrees) or progression of deformity in growing children.
  • Large, tense, non-resolving cold abscess producing secondary mechanical obstruction or sepsis.
  • Diagnostic uncertainty failing needle biopsy.
  • Surgical Procedure: Anterior radical transpleural or retroperitoneal debridement (Hong Kong operation), canal decompression, strut bone grafting, and posterior instrumentation/stabilization.

TBM is the most devastating, neurologically catastrophic, and lethal complication of tuberculosis. Mortality exceeds 30%, and over 50% of survivors suffer permanent neurological sequelae (hemiplegia, cognitive deficit, blindness, or hydrocephalus).

1. During primary bacteremia, tiny subependymal or subpial caseous granulomas seed the cerebral cortex and meninges (Rich foci).
2. Years or months later, a Rich focus undergoes caseous necrosis and ruptures directly into the subarachnoid space.
3. A massive cell-mediated delayed hypersensitivity reaction is unleashed in the basal subarachnoid cisterns, generating a thick, gelatinous, greenish-gray basal exudate.
4. Basilar Entrapment: The exudate coats the circle of Willis and entraps cranial nerves emerging from the brainstem, specifically Cranial Nerves III (Oculomotor), VI (Abducens), and VII (Facial).
5. Vasculitis & Stroke: Intense inflammation of the adventitia and media of the middle and anterior cerebral arteries induces obliterative endarteritis, thrombosis, and cerebral infarction (most commonly in the basal ganglia, internal capsule, and thalamus).
6. Hydrocephalus: The gelatinous exudate obliterates the foramen of Luschka and Magendie and coats the arachnoid villi, producing either non-communicating or communicating hydrocephalus.

• Antitubercular Chemotherapy: Extended 12-month regimen: 2 months 2RHZE followed by 10 months of 4RH. High-dose Isoniazid and Pyrazinamide possess outstanding CSF penetration; Rifampicin achieves 10–20% CSF penetration through inflamed meninges.
• Mandatory Corticosteroid Therapy: Adjuvant systemic steroids are mandatory for ALL patients with TBM regardless of clinical stage to reduce basal exudates, intracranial pressure, vasculitis-induced strokes, and mortality:
  • Intravenous Dexamethasone: 0.4 mg/kg/day for week 1, 0.3 mg/kg/day for week 2, 0.2 mg/kg/day for week 3, and 0.1 mg/kg/day for week 4; followed by transition to oral tapering over an additional 4 weeks (total duration: 6 to 8 weeks).
  • Alternative (Prednisolone): 60 mg/day (or 2 mg/kg/day in children) orally for 2 to 4 weeks, tapered gradually over the subsequent 4 to 6 weeks.
• Neurosurgical Interventions: Ventriculoperitoneal (VP) shunting, external ventricular drainage (EVD), or endoscopic third ventriculostomy (ETV) for acute obstructive hydrocephalus.

• Tuberculous Pericarditis: Granulomatous inflammation of the pericardium presenting with chest pain, venous congestion, and friction rub. Rapid accumulation of fluid causes cardiac tamponade. Chronic healing leads to dense fibrocalcific constrictive pericarditis requiring surgical pericardiectomy. Systemic corticosteroids decrease the risk of constrictive pericarditis.
• Abdominal / Gastrointestinal TB: Primarily involves the ileocecal junction (high lymphoid density in Peyer’s patches) presenting with right lower quadrant pain, mass, and intestinal obstruction. Tuberculous peritonitis presents with fever, weight loss, and painless, "doughy" abdomen with high-protein ascites (serum-ascites albumin gradient [SAAG] < 1.1 g/dL).
• Genitourinary TB: Renal seeding leads to chronic pyuria with repeatedly negative routine bacterial cultures ("sterile pyuria"), microscopic hematuria, hydronephrosis, and autonephrectomy (putty kidney). In females, it attacks the fallopian tubes, leading to bilateral salpingitis, pelvic adhesions, and intractable primary infertility. In males, it causes chronic epididymo-orchitis and beaded vas deferens.
• Miliary Tuberculosis: Disseminated hematogenous tuberculosis characterized by thousands of tiny (1 to 2 mm), yellowish-white, firm granulomas resembling millet seeds seeded throughout the lungs, liver, spleen, bone marrow, and kidneys. Clinically presents with high septic swinging fevers, wasting, hepatosplenomegaly, and choroidal tubercles on fundoscopy. Chest radiograph demonstrates a diffuse, uniform, symmetrical reticulonodular "miliary" infiltrate throughout both lung fields.

Rapid molecular assays are the mandatory first-line initial diagnostic test for all individuals with presumptive TB.

• Technology: Fully automated, closed, hemi-nested real-time Polymerase Chain Reaction (PCR) cartridge platform.
• Mechanism: Multi-color molecular beacons target the 81-base pair core region of the rpoB gene of MTB.
  • Detects M. tuberculosis complex DNA.
  • Simultaneously detects mutations within the rpoB hotspot region conferring Rifampicin resistance (which serves as a reliable surrogate marker for Multidrug-Resistant TB [MDR-TB] in >95% of cases).
• Analytical Sensitivity: The upgraded Xpert MTB/RIF Ultra cartridge incorporates two different multi-copy insertion elements (IS6110 and IS1081), dramatically dropping the limit of detection to 16 colony-forming units (CFU)/mL (compared to 131 CFU/mL for the classic cartridge).
• Turnaround Time: Direct result available within 90 to 120 minutes.
• Validated Specimen Types: Sputum, gastric aspirate, induced sputum, bronchoalveolar lavage (BAL), cerebrospinal fluid (CSF), lymph node aspirates/biopsy tissue, synovial fluid, pleural fluid, and stool samples (particularly validated in pediatric cohorts unable to expectorate).

• Chip-based micro-PCR platform designed for point-of-care operation in rural peripheral primary healthcare facilities. Battery-operated, temperature-resilient, and reports results within 60 minutes.

• Sputum Smear Acid-Fast Microscopy: Light microscopy using Ziehl-Neelsen staining or LED fluorescence microscopy using Auramine-O. Highly specific, but requires a high bacterial threshold (5,000 to 10,000 bacilli/mL of sputum), rendering it frequently false-negative in paucibacillary pediatric TB, extra-pulmonary disease, and advanced HIV immunosuppression. Primarily reserved for monitoring therapeutic bacteriological response at months 2, 5, and 6.
• Mycobacterial Culture (Gold Reference Standard):
  • Solid Media: Lowenstein-Jensen (LJ) egg-based medium (incubated at 37°C for up to 8 weeks).
  • Liquid Media: Mycobacterial Growth Indicator Tube (MGIT) utilizing automated fluorometric oxygen sensors (results within 1 to 3 weeks).
  • Essential for phenotypic Drug Susceptibility Testing (DST) and genomic surveillance.
• Lateral Flow Urine Lipoarabinomannan (LF-LAM): Rapid, point-of-care lateral flow dipstick test that detects LAM antigen shed in the urine of TB patients. Indicated specifically for:
  • HIV-positive inpatients and outpatients with advanced HIV disease (CD4 count ≤ 200 cells/μL, or WHO clinical stages 3 or 4).
  • Any severely ill or hemodynamically unstable HIV-positive patient regardless of CD4 count.

• Chest Radiography (CXR):
  • Post-Primary TB: Focal, patchy, or confluent heterogenous infiltrates in the apical and posterior segments of the upper lobes or superior segments of the lower lobes; dynamic thin- or thick-walled cavitations; volume loss and fibrosis.
  • Primary TB: Unilateral hilar or mediastinal lymphadenopathy; middle/lower lobe consolidation; pleural effusion.
  • Miliary TB: Classical "millet-seed" pattern: bilateral, diffuse, uniform 1–2 mm micro-nodular opacities evenly distributed throughout both lungs.
• Computer-Aided Detection (CAD / Artificial Intelligence): Digital CXR systems utilizing AI algorithms that automatically generate an abnormality score (0–100) for pulmonary TB, enabling massive triage screening in resource-limited or high-volume congregate environments (prisons, mining camps, urban slums).

• Mechanism of Action: A prodrug activated by the mycobacterial catalase-peroxidase enzyme KatG. The activated isonicotinic acyl radical couples with NAD+ to inhibit the enzyme InhA (enoyl-acyl carrier protein reductase), completely blocking the biosynthesis of mycolic acids essential for the mycobacterial cell wall. Highly bactericidal against actively replicating extracellular bacilli.
• Dosage: 5 mg/kg body weight daily (typical adult dose: 300 mg once daily).
• Pharmacokinetics & Metabolism: Metabolized in the liver by N-acetyltransferase 2 (NAT2). The human population is divided into "slow acetylators" (higher drug levels, prone to peripheral neuropathy and hepatotoxicity) and "fast acetylators" (rapid clearance).
• Adverse Effects:
  • Peripheral Neuropathy: INH competitively inhibits pyridoxal phosphokinase and increases the urinary excretion of Pyridoxine (Vitamin B6), causing glove-and-stocking paresthesias. Prevention: Co-administer Pyridoxine 25 to 50 mg daily to all high-risk patients (pregnant women, malnourished individuals, alcoholics, diabetics, and PLHIV).
  • Hepatotoxicity: Asymptomatic transaminase elevation in up to 20% of patients; severe, fatal toxic hepatitis occurs via accumulation of toxic hydrazine metabolites. Discontinue if transaminases rise >3 times upper limit of normal (ULN) with symptoms, or >5 times ULN without symptoms.
  • Drug-Induced Lupus Erythematosus & Central Neurotoxicity: Seizures, optic neuritis, psychosis.

• Mechanism of Action: Binds specifically to the β-subunit of the bacterial DNA-dependent RNA polymerase (encoded by the rpoB gene), physically blocking the elongation of nascent messenger RNA chains. Unmatched, potent bactericidal and sterilizing activity against both actively dividing and slow-metabolizing "persister" bacilli inside necrotic caseum.
• Dosage: 10 mg/kg body weight daily (typical adult dose: 600 mg once daily; taken on an empty stomach 1 hour before or 2 hours after meals).
• Adverse Effects & Pharmacological Interactions:
  • Benign Secretory Discoloration: Imparts a bright orange-red or reddish-brown discoloration to urine, tears, saliva, sweat, and contact lenses. (Universal patient counseling is essential).
  • Potent Cytochrome P450 (CYP3A4) Induction: Rifampicin is one of the most powerful known inducers of the hepatic microsomal CYP450 enzyme system. It massively accelerates the clearance and drops the plasma levels of: protease inhibitors, NNRTIs, oral contraceptives, warfarin, digoxin, sulfonylureas, methadone, and corticosteroids.
  • Hepatotoxicity: Cholestatic jaundice, elevated conjugated bilirubin, and transaminasemia.

• Mechanism of Action: A synthetic prodrug converted by mycobacterial pyrazinamidase (encoded by pncA) into active pyrazinoic acid. Active exclusively in acidic microenvironments (pH ≤ 5.5), such as the hyper-acidic phagolysosomes of macrophages and the borders of caseous necrotic lesions. Disrupts the bacterial membrane potential and collapses intracellular ATP synthesis. Possesses unique sterilizing activity against semi-dormant intracellular bacilli.
• Dosage: 25 mg/kg body weight daily (typical adult dose: 1,500 mg to 2,000 mg once daily).
• Adverse Effects:
  • Hyperuricemia & Arthralgia: Metabolites inhibit the renal excretion of uric acid, producing asymptomatic hyperuricemia and non-gouty polyarthralgia in >50% of patients. Frank acute gouty arthritis may occur.
  • Dose-Dependent Hepatotoxicity: Pyrazinamide is the most hepatotoxic of all standard first-line antitubercular medications.

• Mechanism of Action: Inhibits the enzyme arabinosyl transferase III (encoded by embB), blocking the polymerization of arabinose into arabinogalactan, halting cell wall biosynthesis. Unlike HRZ, Ethambutol is primarily bacteriostatic. Its primary role in first-line therapy is to prevent the emergence of drug resistance mutations to companion drugs.
• Dosage: 15 to 20 mg/kg body weight daily (typical adult dose: 800 mg to 1,200 mg once daily). Excreted predominantly by the kidneys; dose adjustment required in renal insufficiency.
• Adverse Effects:
  • Retrobulbar / Optic Neuritis: Dose- and duration-dependent toxicity. Manifests as decreased visual acuity, central scotomas, and loss of red-green color discrimination (dyschromatopsia). Mandatory baseline and periodic visual acuity and Ishihara color testing. Strictly avoid or use with caution in young children unable to report visual changes reliably.

Administered using Fixed-Dose Combination (FDC) tablets (RHZE: 150/75/400/275 mg; RH: 150/75 mg) to ensure adherence and prevent monotherapy:

• Non-Severe Pediatric TB: World Health Organization guidelines recommend a 4-month regimen (2RHZ / 2RH) for children aged 3 months to 16 years with non-severe, smear-negative pulmonary TB or peripheral lymphadenitis.
• Severe Pediatric Pulmonary TB or Suspected Resistance: Standard 6-month regimen: 2 months of daily RHZE followed by 4 months of daily RH (2RHZE / 4RH) using child-friendly dispersible FDC tablets.
• Pediatric TBM and Spinal TB: 12 months total therapy: 2RHZE / 10RH.

• Definitions:
  • Rifampicin-Resistant TB (RR-TB): Resistance to rifampicin detected with or without resistance to other drugs.
  • Multidrug-Resistant TB (MDR-TB): Resistance to at least both Isoniazid and Rifampicin simultaneously.
  • Pre-Extensively Drug-Resistant TB (Pre-XDR-TB): MDR/RR-TB with additional resistance to any fluoroquinolone (Levofloxacin or Moxifloxacin).
  • Extensively Drug-Resistant TB (XDR-TB): MDR/RR-TB resistant to any fluoroquinolone AND at least one additional WHO Group A drug (Bedaquiline or Linezolid).
• The Modern Standard: Shorter All-Oral 6-Month BPaLM / BPaL Regimen:
  • Completely supersedes older 9- to 24-month toxic injectable regimens containing kanamycin/amikacin.
  • Composition: Bedaquiline (B), Pretomanid (Pa), Linezolid (L), and Moxifloxacin (M) administered for 6 months (BPaL is used if fluoroquinolone resistance is documented).
  • Bedaquiline (Group A): Diarylquinoline; inhibits mycobacterial ATP synthase. Causes QTc interval prolongation (requires serial baseline and routine ECG monitoring).
  • Pretomanid: Nitroimidazooxazine; inhibits mycolic acid biosynthesis and induces respiratory poisoning via nitric oxide release under anaerobic conditions.
  • Linezolid (Group A): Oxazolidinone; inhibits protein synthesis at the 50S ribosomal subunit. Requires intensive monitoring for myelosuppression (anemia, thrombocytopenia, leukopenia) and mitochondrial toxicities (peripheral neuropathy, irreversible optic neuritis, and lactic acidosis).

TPT is the systematic administration of antitubercular medicines to individuals with documented latent infection or documented high risk of exposure to prevent progression to active clinical disease.

1. People Living with HIV (PLHIV): All adults, adolescents, and children living with HIV, irrespective of CD4 count, ART status, or pregnancy, once active TB is ruled out.
2. Household Contacts of Pulmonary TB:
   • All children aged < 5 years in household contact with a bacteriologically confirmed pulmonary TB index case (highest risk of fatal miliary TB or TBM).
   • All children ≥ 5 years, adolescents, and adult household contacts.
3. Clinical Risk Groups: Patients initiating anti-TNF-α biologic therapies, systemic immunosuppressive therapy/long-term steroids, hemodialysis patients, and silicosis sufferers.

DANGER: Never initiate TPT without rigorously ruling out active TB. Providing monotherapy or dual therapy to an individual with active TB rapidly induces drug resistance!

• Screen for the presence of the 4 Cardinal Symptoms: (1) Current cough of any duration, (2) Fever, (3) Unexplained weight loss, and (4) Night sweats.
• If ANY symptom is present, the patient is presumed to have TB: perform immediate sputum GeneXpert Ultra and digital chest radiography. If negative, reconsider TPT.
• If ALL four symptoms are absent, active TB is excluded with >95% negative predictive value: initiate TPT immediately.

• Impact of HIV on TB: HIV depletes and disorganizes CD4+ T-lymphocytes, destroying granuloma structural integrity. Latent TB reactivation risk surges from 10% per lifetime in HIV-negative individuals to 10% per year in untreated PLHIV. PTB manifests atypically (frequently smear-negative, lower-lobe infiltrates without cavities, high rates of miliary and fatal extra-pulmonary disease).
• Impact of TB on HIV: Mycobacterial cell wall components stimulate CD4+ T-cell chemokine receptors (CCR5 and CXCR4), triggering nuclear factor kappa B (NF-κB) transcription, massively multiplying HIV viral load, and accelerating progression to Stage 4 AIDS and death.

1. Initiate Anti-TB Therapy First: Always stabilize the patient on antitubercular therapy first.
2. Timing of ART:
   • Standard PTB / Non-CNS EPTB: Initiate ART within 2 weeks of starting TB treatment, regardless of CD4 count. (Early ART markedly drops mortality).
   • CRUCIAL EXCEPTION — Tuberculous Meningitis: In TBM, immediate early ART is dangerous. Rapid immune reconstitution within the closed intracranial vault produces catastrophic intracranial hypertension, severe brainstem herniation, and death. Delay ART initiation for 4 to 8 weeks after starting TB chemotherapy and high-dose corticosteroids.

• Mechanism: Rapid restoration of pathogen-specific CD4+ T-cells following ART initiation triggers a massive, dysregulated hyper-inflammatory cytokine storm directed against viable or dead mycobacterial antigens.
• Forms:
  • Paradoxical TB-IRIS: A patient with known TB on active therapy who was clinically improving suddenly develops high spiking fevers, expanding lymph nodes, enlarging pleural effusions, or worsening pulmonary infiltrates shortly after commencing ART.
  • Unmasking TB-IRIS: An occult, subclinical, undiagnosed TB infection presents precipitously as an acute, severe, hyper-inflammatory illness immediately following ART start.
• Management: DO NOT STOP ART; DO NOT STOP TB MEDICATION. Continue both therapies. Administer oral Prednisone (1.0 to 1.5 mg/kg/day) tapered over 4 weeks to suppress inflammatory damage. Aspirate tense, fluctuant cold abscesses.

• Massive Hemoptysis: Defined as expectoration of >200 to 600 mL of blood in 24 hours. Represents acute asphyxiation emergency from cavitary necrosis or Rasmussen aneurysm rupture.
• Spontaneous Secondary Pneumothorax: Rupture of an apical tuberculous cavity directly through the visceral pleura into the pleural space. Rapidly progresses to a life-threatening tension pneumothorax or bronchopleural fistula.
• Tuberculous Empyema & Fibrothorax: Chronic purulent effusion leads to extensive pleural calcification and dense collagen deposition ("pleural peel"), entrapping the lung, collapsing hemithorax compliance, and requiring surgical decortication.
• Post-TB Lung Disease (PTLD): Widespread residual cicatricial scarring, architectural distortion, traction bronchiectasis, and destructive emphysema resulting in permanent chronic obstructive pulmonary disease (COPD) and chronic respiratory insufficiency.
• Aspergilloma ("Fungus Ball"): Saprophytic colonization of a pre-existing, healed, open tuberculous cavity by Aspergillus fumigatus. Manifests with recurrent, refractory hemoptysis. Chest X-ray displays a mobile, round intracavitary mass topped by a crescent of air (Monod’s sign).
• Cor Pulmonale: Extensive destruction of the pulmonary capillary bed by fibro-cavitary disease leads to severe chronic pulmonary hypertension, right ventricular hypertrophy, and right-sided congestive heart failure (jugular venous distension, hepatomegaly, ascites, peripheral edema).

• Systemic AA Amyloidosis: Chronic, longstanding, uncontrolled inflammatory stimulation drives the hepatic synthesis of serum amyloid A (SAA) protein, which deposits as insoluble β-pleated fibrils in the renal glomeruli (nephrotic syndrome), spleen, liver, and myocardium.
• Obstructive Hydrocephalus & Ischemic Stroke: Permanent complications of TBM producing lifelong cognitive deficits, cranial nerve palsies, or spastic paraplegia.
• Addisonian Crisis: Granulomatous destruction of >90% of the adrenal cortex produces primary adrenal insufficiency (Addison's disease) characterized by hyperpigmentation, severe hypotension, hyponatremia, hyperkalemia, and cardiovascular collapse during physiological stress.

• Triage: Immediately identify, separate, and fast-track all patients presenting with chronic cough at health facility entry points.
• Cough Etiquette: Issue surgical masks or paper tissues to coughing patients immediately upon triage arrival. Instruct them to cover mouth and nose during coughing/sneezing.
• Rapid Diagnosis & Treatment: Shorten the time from sputum collection to GeneXpert results, immediately initiating effective chemotherapy. (An effective regimen renders the patient largely non-infectious within 2 weeks).

• Maximize Natural Ventilation: Cross-ventilation in consultation rooms, waiting areas, and wards by keeping opposing windows and doors open continuously. Maintain a minimum ventilation rate of 60 to 120 liters/second/patient (or >12 air changes per hour [ACH]).
• Mechanical Negative Pressure Ventilation: Specialized airborne infection isolation rooms (AIIR) maintaining negative air pressure relative to corridors (-2.5 Pa) with exhaust discharged outdoors away from air intakes.
• Upper-Room Ultraviolet Germicidal Irradiation (UVGI): Specialized shielded UV-C fixtures emitting light at 254 nm in upper room air spaces to destroy airborne bacilli in stagnant or cold climates.

• Healthcare workers caring for patients with infectious pulmonary TB or undergoing aerosol-generating procedures (sputum induction, bronchoscopy, intubation) must wear properly fit-tested particulate respirators (N95, FFP2, or equivalent).
• Important Distinction: Ordinary surgical masks protect others from the wearer's droplets, but do NOT filter microscopic airborne droplet nuclei. Respirators protect the healthcare worker from inhaling infectious aerosols.

• Adherence Counseling: Take all tablets once daily on an empty stomach. Emphasize that taking pills intermittently or stopping early causes the bacteria to mutate into incurable Drug-Resistant TB (DR-TB).
• Color Changes: Reassure the patient that tears, sweat, saliva, and urine will turn reddish-orange from Rifampicin; this is completely harmless.
• Hepatotoxicity Warning Signs: Instruct the patient to stop medication and report immediately if they develop: yellow eyes (jaundice), dark tea-colored urine, persistent vomiting, or right upper quadrant abdominal pain.
• Home Hygiene: Sleep alone in a well-ventilated room with open windows during the first 2 weeks of therapy. Avoid crowded public transport, enclosed spaces, and contact with infants or unvaccinated children.
• Household Contact Screening: Bring all household members, particularly children under 5 years and PLHIV, to the clinic for screening and initiation of Tuberculosis Preventive Treatment (TPT).

• Doctors Revision Uganda. Clinical Guide: Tuberculosis (TB) Disease Management. Available at: https://doctorsrevisionuganda.com/clinical-guide/tuberculosis-tb-disease-management/ [Accessed 2026].
• Doctors Revision Uganda. Clinical Guide: Tuberculosis of the Spine (Pott's Disease). Available at: https://doctorsrevisionuganda.com/clinical-guide/tuberculosis-of-the-spine-potts-disease/ [Accessed 2026].
• Doctors Revision Uganda. Clinical Guide: Tuberculosis Preventive Treatment (TPT). Available at: https://doctorsrevisionuganda.com/clinical-guide/tuberculosis-preventive-treatment-tpt/ [Accessed 2026].
• Doctors Revision Uganda. Clinical Guide: Tuberculous Meningitis (TB Meningitis / TBM). Available at: https://doctorsrevisionuganda.com/clinical-guide/tuberculous-meningitis-tb-meningitis/ and https://doctorsrevisionuganda.com/clinical-guide/tuberculous-meningitis-tbm/ [Accessed 2026].
• World Health Organization. WHO Consolidated Guidelines on Tuberculosis: Module 4: Treatment - Drug-Susceptible Tuberculosis Treatment. Geneva: World Health Organization.
• World Health Organization. WHO Consolidated Guidelines on Tuberculosis: Module 5: Management of Tuberculosis in Children and Adolescents. Geneva: World Health Organization.
• Ministry of Health Uganda. National Tuberculosis and Leprosy Control Programme (NTLP) Manual for Health Workers. Kampala: Ministry of Health Uganda.