GP/ medicine - Tuberculosis Flashcards
(51 cards)
What microorganism causes TB?
Mycobacteria tuberculosis
But can also be caused by Mycobacteria bovis and Mycobacteria africanum
Is Mycobacteria tuberculosis a bacillus or a coccus?
A bacillus (rod)
Can normal gram stain differentiate M.tuberculosis from other bacteria?
NO!
M.tuberculosis is special in the sense that it cannot be stained by normal gram stain i.e. neither gram + nor gram.
It’s an acid-fast bacilli, which means it can only be stained with acid-fast stain
What acid-fast stain do we normally use to identify mycobacteria? what color does that stain have?
Ziehl-Neelsen stain
It’s a light-blue stain
On a CXR, where would you usually see the consolidation in a patient with TB?and why?
- Upper lung lobes (usually at the apex) because it’s where most oxygen is present and TB is an aerobe!
- Cavitation, pleural effusion, mediastinal or hilar lymphadenopathy
Oxygen makes TB have orgasm!!!!
Compare and contrast TB and pneumonia
Where in the world TB is usually found?
Asia, Africa, South America, Eastern Europe
How is TB transmitted?
Aerosol inhalation causes pulmonary infection
Then from the lungs, it can spread all over the body through blood (haematogenous spread), causing extrapulmonary TB
What is the pathology/ pathogenesis of TB?
- Infected aerosols inhaled into the lungs
- Alveolar macrophages engulf the bacteria and carry them to hilar lymph nodes in attempt to control infection
- The lung lesion (Ghon focus) + hilar lymph nodes = Ghon complex
- Small granulomas (tubercles) are formed by macrophages to wall off and contain TB, preventing it from spreading.
- Granulomas are basically a collection of epitheliod histiocytes, lymphocytes and Langerhans giant cells surrounding a cheese-like core, which indicates caseous necrosis in the centre
- If infection is not adequately contained by granulomas, it can invade the bloodstream and cause Extrapulmonary TB and Miliary TB
- The inflammatory response is mediated by a type 4 hypersensitivity reaction
- Progression of TB then follows one of two paths:
- Active disease (primary TB) - symptomatic and infectious - the most common presentation (> 50%), OR
-
Latent disease - asymptomatic and NOT infectious - of which there are 2 outcomes:
- Heals spontaneously and no disease develops - common in healthy individuals
- Reactivation –> secondary TB (or post-primary TB) which is an active disease - patient is symptomatic and infectious
- Usually occurs if a patient becomes immunocompromised e.g. old age, HIV, malignancy, steroids, malnutrition
-
The lungs remain the most common site for secondary TB, however, extrapulmonary TB and miliary TB may occur in immunocompromised patients, esp in the following areas:
- CNS –> TB meningitis (most serious complication)
- Vertebral bodies –> Pott’s disease
- Cervical lymph nodes –> Scrofuloderma
- Renal
- GI tract
What are the risk factors for TB?
PMHx of TB
Close contact with someone with TB
Born in a country with high TB incidence e.g. India, Pakistan, Bangladesh
Foreign travel to country with high TB incidence
Immunosuppression e.g. HIV, organs transplant recipients, renal failure/ dialysis, malnutrition, diabetes, steroids, chemotherapy
Hx of alcohol excess, smoking, and IVDU
Children < 5 yrs old (higher risk of developing extrapulmonary TB)
Give 3 complications of TB
Bronchiectasis
Multi-drug resistance (MDR) TB
COPD
Cor pulmonale
What are the symptoms and signs of pulmonary TB?
Symptoms of pulmonary TB:
- Persistent productive cough with purulent sputum
- Fever
- Weight loss
- Drenching night sweats
- Haemoptysis (late)
- Dyspnoea
Signs:
- Crackles and bronchial breathing
- Pleural effusion
- If severe –> atelectasis, pneumonia, bronchiectasis
What are the clinical features of extrapulmonary TB?
- Genitourinary - sterile pyuria, salpingitis, abscess, epididymitis in males, haematuria
- MSK - arthritis, pott’s disease (back pain), osteomyelitis
- CNS - TB meningitis (headache, photophobia, neck stiffness, confusion, cranial nerve abnormalities, vomiting)
- GI - Ileocaecal lesions - abdominal/ pelvic pain, constipation, bowel obstruction, hepatosplenomegaly
- Skin - erythema nodosum, scrofuloderma
- Lymph nodes - lymphadenopathy often affecting cervical or supraclavicular lymph nodes
- Cardiac - TB pericarditis (pericardial rub, Kussmaul’s sign, fever, cardiomegaly, cough, SOB, chest pain, ankle swelling) –> pericardial effusion and tamponande
- Kussmaul’s sign = a paradoxical rise in jugular venous pressure (JVP) on inspiration, or a failure in the appropriate fall of the JVP with inspiration.
Miliary (disseminated)
. .
What are the differentials for haemoptysis?
PE
Bronchiectasis
TB
Pneumonia
Lung cancer
What investigations would you carry out to screen for latent TB?
CXR
quantiFERON (IGRA) or T-spot test
Mantoux test (tuberculin sensitivity test)
What are the limitations of quantiFERON?
- It only tells you whether you have previously been infected with TB i.e. latent TB infection. It doesn’t differentiate between active and latent TB
* A + quantiFERON test does not mean that the patient has active TB and a - quantiFERON test does not mean that the patient doesn’t have active TB - Patients with immunosuppression may not release IFN-y, causing false negatives
- It can’t pick up non-TB mycobacteria
How does quantiFERON work?
It detects the amount of IFN-y released by T cells when they are exposed to proteins found on mycobacteria. Pre-exposed cells release more IFN-y
Why is IGRA a better test over the Mantoux test?
- It can distinguish latent TB from previous BCG vaccine
- It can distinguish TB mycobacteria from non-TB mycobacteria, so it won’t give any false positives if the patient is infected by non-TB mycobacteria. It only gives a positive result if it’s caused by TB-mycobacteria
What is Mantoux? How is it being carried out?
0.1 mL of purified protein derivative (PPD) injected intradermally
Result read 2-3 days
Erythema and induration > 10 mm = positive result - this implies previous exposure to TB including BCG vaccine
If strongly positive (> 15 mm), TB is likely (as response to previous BCG decreases with time), needs further investigation including e.g. CXR, sputum smear
Causes of false-positive Mantoux test
Previous BCG vaccination
Infection with non-TB mycobacteria
Incorrect method of TST administration
Incorrect interpretation of reaction
Causes of false-negative Mantoux test
Immunosuppression - miliary TB, AIDS, steroids
Sarcoidosis
Lymphoma
Extremes of age
Fever
Hypoalbuminaemia, anaemia
How do you differentiate active TB from latent TB?
Usually based on symptoms and findings on CXR
But the following investigations can help too:
- Sputum smear microscopy (with Ziehl-Neelsen stain)
- TB culture
- NAAT
- Histology - TB granuloma
Which group(s) of people needs IGRA screening for latent TB ?
IGRA tests are used in asymptomatic patients who are at high risk of latent TB infection:
- Immigrants from high TB prevalence countries
- Healthcare workers
- People who have been in contact with a person with active pulmonary or laryngeal TB
- Patients who are immunocompromised e.g. HIV + patients, organ transplant recipients
- For people who have evidence of TB scarring or untreated fibrotic changes on chest X-ray but have not completed treatment as planned
What investigations would you carry out in someone with active TB?
- CXR - cavitation/ pleural effusion/ mediastinal or hilar lympadenopathy
- CT - lymphadenopathy/ nodes with central necrosis
- MRI - leptomeningeal enhancement in TB meningitis
-
TB culture (gold standard) - however this can take 6 weeks:
- Pulmonary TB - send 3 sputum samples for sputum smear microscopy and culture
- Meningeal TB - lumbar puncture
- Pericardial TB - pericardiocentesis
- Gastrointestinal TB - colonoscopy + biopsy
- Lymph node TB - biopsy of lymph node
- Histology - shows caseating granulomas
- Blood tests - FBC, U&Es, LFT
- HIV test
- Check vitamin D
In primary care:
- CXR + 3 sputum samples if active pulmonary TB
- Be aware that false negative results are more common in children and the immunocompromised, such as people with HIV.
