Tuberculosis Flashcards
What causes tuberculosis?
The Mycobacterium tuberculosis complex includes M. tuberculosis (majority of cases), M. bovis and M. africanum
How can tuberculosis be contracted?
Through droplet inhalation and is therefore spread by coughing and sneezing
What happens after exposure to TB?
After exposure to TB, the mycobacterium is engulfed by macrophages in the lung.
Most people clear the infection at this point and have a spontaneous recovery. Those who do not clear it develop primary TB.
What does primary TB lead to in most people?
Primary TB leads to asymptomatic latent TB in most people.
Latent TB can re-activate in 10%, causing post-primary TB.
What do a small number of people with primary TB end up developing?
A small number of people with primary TB develop primary progressive pulmonary or extra-pulmonary TB through haematogenous dissemination
What is military TB?
A disseminated form of TB commonly found in the lungs, which can develop from primary progressive or post-primary TB.
Risk factors
Close contact with a patient infected with pulmonary TB
Demographic features - increased risk of TB are ethnic minorities, those born in or travelling from high prevalence areas (India and sub-Saharan Africa), extremes of age and homelessness.
Some medical conditions or medications can increase the risk of contracting TB or reactivation of latent TB. These include alcohol and drug dependency, immunosuppression (including HIV), malignancy, diabetes, long term steroid use and end-stage renal disease.1
Clinical features
Primary TB is often asymptomatic, and symptoms of primary progressive or post-primary TB are varied.
Typical symptoms of TB may include:1
General: fever, lethargy, anorexia, weight loss, enlarged and tender lymph nodes
Pulmonary: cough (usually chronic), sputum (initially dry, then purulent or blood-stained), breathlessness, pleuritic chest pain
Extra-pulmonary: genitourinary (urinary symptoms), musculoskeletal (joint pain), neurological (headache, reduced GCS, focal neurology), cardiac (chest pain), gastrointestinal (abdominal pain, bloating), rash
Clinical examination
Sputum pots with purulent or blood-stained sputum
Enlarged, tender lymph nodes
Crackles or bronchial breathing over consolidation
Dullness to percussion and decreased fremitus over pleural effusions
Differential diagnosis
Bacterial pneumonia or viral respiratory tract infection
Interstitial lung disease
Malignancy including lymphoma
Sarcoidosis
Bedside investigations
Urine dip: sterile pyuria in genitourinary TB
ECG: small complexes suggestive of pericardial effusion or ST-T wave changes in pericarditis
Imaging
The most useful initial imaging is a chest X-ray.
A CT chest can be used to further characterise pulmonary lesions or investigate for differential diagnoses.
How will a pulmonary TB present itself on an X-ray
Patchy or lobar consolidation
Linear and nodular opacities
Miliary TB (small, uniformly distributed nodules)
Cavitating lesions (more likely in post-primary TB)
Tuberculoma (a caseating granuloma)
Calcified tuberculoma (known as a Ghon focus) or lymph nodes
Lymphadenopathy
Pleural effusion
What should you do when you diagnose a patient with TB to minimise harm to the public?
TB is a notifiable disease under the Public Health (Infectious Diseases) Regulations 1988.1 Screening should be offered to any close contacts of a person with active TB.
Patients with suspected TB should be managed in a single room or a negative pressure room if they are considered high risk.
Treatment
2 antibiotics (isoniazid and rifampicin) for 6 months
2 additional antibiotics (pyrazinamide and ethambutol) for the first 2 months of the 6-month treatment period
