Tuberculosis (summary)

This is a basic article for medical students and other non-radiologists

Tuberculosis (TB) is a mycobacterial airborne infection that is typically asymptomatic in children but can reactivate in later life causing a destructive cavitating contagious pneumonia. Occasionally TB spreads through the bloodstream to infect the brain and other organs.

Reference article

This is a summary article; read more in our article on tuberculosis.

Summary

• epidemiology

  • according to the WHO 2023 report ¹:

    • globally TB causes more deaths than any other infectious disease

    • in 2022 it was estimated that 10.6 million people became ill with TB

    • most cases were in Southeast Asia (46%), Africa (23%) and the Western Pacific (18%)

    • around 6.3% of cases occurred in people living with HIV

    • diagnosis and treatment were disrupted by the COVID pandemic

• presentation

  • ​primary infection

    • usually asymptomatic

    • may feel generally unwell or have a small pleural effusion

  • post-primary infection

    • non-specific systemic symptoms can lead to delayed diagnosis

      • malaise

      • weight loss

      • fever

      • night sweats

    • pulmonary symptoms

      • productive cough (mucopurulent or blood-stained)

      • shortness of breath

      • chest pain

    • extrapulmonary symptoms

      • depends on location of disease

• pathology

  • M. tuberculosis

    • aerobic mycobacterium

    • Gram staining ineffective due to waxy coating

  • primary infection

    • first exposure to M. tuberculosis

    • the lung infection may be occult or may be visible as an area of consolidation in the mid or lower zone (Ghon focus)

    • more commonly hilar and/or paratracheal lymphadenopathy are seen

    • most primary infections are asymptomatic and are contained remaining dormant (latent TB)

    • occasionally the host immune system does not contain the bacterium, and this leads to progressive primary TB or hematogenous spread (miliary TB)

  • post-primary TB is due to reactivation of infection when the immune system is impaired due to old age, immunosuppressive drugs, etc.

    • dormant bacteria are no longer contained and multiply in the lungs causing:

      • destructive cavitating upper zone pneumonia

      • multiplication of organisms within the cavities

      • airway communication with cavities leading to:

        • endobronchial spread within the lungs

        • airborne spread to others

  • miliary tuberculosis

    • disseminated disease spreads through the blood

    • tuberculomas in brain, kidney, bone, etc

    • tuberculous meningitis

    • may follow primary or post-primary infection

    • poor prognosis

  • TB in HIV-AIDS presents with a primary pattern; immune compromise means that the body responds as if it is a first exposure

    • miliary disease is common

• investigation

  • chest X-ray

  • sputum sample

    • Ziehl-Neelsen stain for acid-fast bacilli

    • culture for confirmation of diagnosis and sensitivity testing

  • blood tests

    • interferon gamma release assay (IGRA)

    • GeneXpert nucleic acid amplification test and antibiotic sensitivity

  • HIV serology

  • brain MRI (miliary TB)

  • lumbar puncture

    • investigation for TB meningitis 

• treatment

  • active TB

    • four-drug regimen of rifampin, isoniazid, pyrazinamide and ethambutol (2 months)

    • continuation of rifampin and isoniazid (4 months)

  • latent TB

    • rifampin and isoniazid (3 months)

    • OR isoniazid alone (9 months)

    • OR rifampin alone (4 months)

  • multidrug-resistant TB is an increasing problem

• screening and prevention

  • when active TB is suspected, precautions need to be taken to avoid airborne spread

  • screening for latent TB

    • Mantoux test (tuberculin skin test)

    • interferon gamma release assay (IGRA)

  • BCG vaccine

    • recommended for high-risk groups

• contact-tracing

  • TB is a notifiable disease

  • primary infection is the result of close contact with a contagious individual, often a family member

  • reactivation tuberculosis is associated with cavities in which organisms breed and these can be spread by coughing

  • genetic fingerprinting of the organisms has cast doubt on the reliability of imaging to distinguish primary infection from reactivation ²

Radiographic features

The manifestations of TB are strongly influenced by host immunity.

Chest radiograph

• primary infection

  • parenchymal consolidation

  • lymphadenopathy - most frequent manifestation

  • pleural effusion

  • Ghon complex (consolidation plus lymphadenopathy)

• post-primary infection

  • patchy consolidation and cavitation (upper zones)

  • healing results in fibrosis and calcification

• miliary tuberculosis

  • innumerable 1-3 mm diameter miliary nodules

  • uniform size and distribution throughout both lungs

• thoracic spine infection may be apparent as bone destruction and paraspinal mass

CT chest

CT is far more sensitive and demonstrates lesion characteristics which are helpful in diagnosis:

• central necrosis in lymph nodes

• areas of consolidation which may be occult on CXR

• effusions

• empyema

• cavitation

• endobronchial spread (tree in bud opacities)

• miliary nodules

• signs of latent disease such as calcified granulomata and upper zone fibrocalcific disease