S9) Tuberculosis Flashcards
What is tuberculosis?
Tuberculosis is a bacterial infection caused by Mycobacterium tuberculosis which mainly affects the lungs, but can affect any part of the body (abdomen, glands, bones and nervous system)
Identify 3 common organisms which cause TB
- M tuberculosis (most common)
- M bovis
- M africanum
Describe the structure of mycobacterium tuberculosis
- Non-motile rod-shaped bacteria
- Obligate aerobe
- Long-chain fatty acids (structural rigidity)
- relatively slow growing
How is TB transmitted?
Spread is by respiratory droplets e.g. coughing, sneezing, etc
How easily can TB be transmitted?
- Contagious, but not easy to acquire infection
- Prolonged exposure facilitates transmission (at-least 8 hours/day up to 6 months)
In 6 steps, outline the pathogenesis of TB
⇒ Inhaled infectious droplets
⇒ Engulfed by alveolar macrophages but cant kill
→ Th1 or CD+4 activate macrophages to kill MTB (4-6weeks)
⇒ Travels to local lymph nodes
⇒ Primary complex (primary infection – Ghon’s focus)
⇒ Initial containment of the infection (latent infection)
⇒ Either: heals/self cure (95%) OR reactivates to post primary TB
What is a Ghon’s focus?
Ghon’s focus is a calcified tuberculous caseating granuloma which represents the sequelae of primary pulmonary tuberculosis infection
Ghons complex: primary ghons focus and draining lymph nodes together
Distinguish between Latent TB and TB disease in terms of the following:
- Activity
- Chest X-Ray
- Sputum
- Symptoms
- Transmission
- Testing
What is post-primary TB?
- Post-primary tuberculosis is a condition which usually occurs during the two years following the initial infection (can occur at any point)
- Reactivation frequently occurs in the setting of decreased immunity and usually involves the lung apex
What is latent TB?
A latent tuberculosis infection (LTBI) is a condition wherein a patient is infected with Mycobacterium tuberculosis, but the infection is contained by the host’s body and is not active
Identify 5 risk factors for the reactivation of latent TB
- HIV infection
- Substance abuse
- Prolonged corticosterioid therapy
- Diabetes Mellitus (poorly controlled)
- Organ transplant (immunosuppression)
Describe the pathology & histology of tuberculosis
A caseating granuloma appears in the lung parenchyma and mediastinal lymph nodes
very prominent feature of TB
a granuloma is rich in immune cells: macrophages, dendrites, neutrophils
Identify the sites of pulmonary, extrapulmonary and miliary TB respectively
- Pulmonary TB: lungs
- Extrapulmonary TB: larynx, lymph nodes, pleura, brain, kidneys
- Miliary TB: all other parts of the body (through the bloodstream)
Most cases of TB are pulmonary and miliary TB is rare.
When is extra-pulmonary TB most commonly seen?
- HIV-infected
- Immunosuppressed persons
- Young children
Outline the clinical approach for a patient with suspected TB
- Index of suspicion
- Suggestive symptoms (history)
- Investigations
- Treatment
- Prevent transmission
Identify 5 groups of people in whom one should suspect TB
- Non-UK born/recent migrants (South Asia/Sub-Saharan Africa)
- HIV
- Immunocompromised people
- Homeless
- Drug users
Identify 5 key parts of the history of a patient with suspected TB
- Ethnicity
- Travel history (high TB burden countries)
- Contacts with TB
- BCG vaccination?
- Specific clinical features
Identify 5 symptoms of TB
- Fever
- Night sweats
- Weight loss and anorexia
- Tiredness and malaise
- Cough (haemoptysis occasionally)
Identify 5 signs of TB
- Pyrexia
- Weight loss
- CXR abnormality
- Crackles in affected area
- Fibrosis (in extensive disease)
those infected have 10% risk of developing active disease of which 5% develop primary TB at time of infection and another 5% develop post primary
Identify 4 investigations one can request for when treating a patient with suspected TB
- Chest X Ray
- Sputum (3 early morning samples)
- Induced sputum
- Bronchoscopy
Why is the apex of the lung often affected by TB?
The apex of the lung is the most oxygenated region of the lung and Mycobacterium tuberculosis is an aerobe
Describe the radiological appearances of TB
- Ill-defined patchy consolidation
- Cavitation develops within consolidation
- Healing results in fibrosis
- Pleural effusion (if pleural involvement)
Identify 5 laboratory tests used for TB
- Sputum culture (gold standard)
- Gastric acid aspirates (in kids)
- NAAT
- Chromatography
- Drug sensitvity (for treatment)
What is the tuberculin sensitivity test?
TST/ Mantoux test is a diagnostic test for TB wherein tuberculin is injected into the patient intradermally to observe a skin reaction if one has been exposed to TB
What are the problems with the Mantoux test?
- False positives (BCG)
- False negatives (immunocompromised – HIV/drugs)
- Subject to interpretation
What is involved in interferon gamma releasing assays?
Detection of antigen-specific IFN-gamma production
this is produced by lymphocytes activating macrophages to kill MTB
What are the problems with interferon gamma releasing assays? (tuberculin skin tests)
- Cannot distinguish latent & active TB
- Similar problems with sensitivity & specificity
What are the three ways of treating TB?
- Multi-drug therapy (RIPE)
- Vitamin D
- Surgery
TB treatment involves early and adequate treatment with anti TB drugs.
Outline the multi-drug therapy in TB as well as the associated side effects (RIPE)
- Rifampicin – raises transaminases & induces cytochrome P450 (orange secretions)
- Isoniazid – peripheral neuropathy & hepatotoxicity
- Pyrazinamide – hepatotoxicity
- Ethambutol – visual disturbance
- vit D or surgery
Describe the duration of TB treatment
- 3/4 drugs (2 months): rare that the infection will be resistant to all 3
- Rifampicin & Isoniazid (4 months)
18 months if CNS TB
How does one ensure adherence to TB medication?
- Directly observed therapy (DOT)
- Video observed therapy (VOT)
What are the two types of drug resistant TB?
- Multi-drug resistant TB (MDR) – resistant to rifampicin & isoniazid
- Extremely drug-resistant TB (XDR) – also resistant to fluoroquinolones & at least 1 injectable
What causes drug resistant TB?
- Spontaneous mutation
- Inadequate treatment
What increases the likelihood of drug resistant TB?
- Previous TB treatment
- HIV infection
- Known contact of MDR TB treatment
- Failure to respond to conventional
What is miliary tuberculosis?
- Miliary tuberculosis (TB) is the widespread dissemination of Mycobacterium tuberculosis via haematogenous spread
- It occurs either during primary infection or during reactivation and often multiple organs involved (including the lungs)
Which systems are often affected in extra-pulmonary TB?
- Lymphatic system
- GI system : swallowing of tubercles
- GU system: progress to real disease
- MSK system
- CN system: meningitis
bone and joints
How does lymphadenitis present in extra-pulmonary TB?
- Scrofula
- Cervical lymph nodes (most commonly)
- Abscesses & sinuses
Describe how extra-pulmonary TB affects the genitourinary system
- Slow progression to renal disease
- Subsequent spreading to lower urinary tract
Describe how extra-pulmonary TB affects the musculoskeletal system
- Spinal TB (most common)
- Pott’s disease
Describe how extra-pulmonary TB affects the central nervous system
- Chronic headache
- Fevers
- Lymphocytosis
Describe the principles of controlling TB
- Detection and treatment of cases and contacts
- Prevention of transmission: PPE, negative pressure isolation
- Reduce susceptible contacts: address risk factors, vaccination
What is the BCG vaccine?
BCG vaccine is a vaccine primarily used against tuberculosis wherein a live attenuated M. bovis strain is injected into babies in high prevalence communities only
what is the difference between infection and active disease
infection refers to the presence of the MTB in the body
if the infection is symptomatic then it is an active disease if not then it is a latent infection
when can the infection be reactivated
- when the person is immune compromised or aging
- diabetes mellitus
- HIV
why is there less hilar lymphadenopathy in secondary TB
- due to first infection immune system is already primed against MTB
- walls of focus if infection from the regional lymph nodes
what are some effects of secondary TB
- sputum and haemopytsis
- cavity formation: softening of the caseous material is discharged into the bronchus. Fibrous tissue develops around it
- haemorrhage: due to extensions from the caseous process spreading into vessels → haemopytysis
- spread to involve the rest of the lung → caseous and liquified material spread the infection through bronchial tree to other zones
- pleaural effusion: seeding of TB in pleura can result In effusion
how to diagnose TB
ACTIVE: acid - fast acting smear
LATENT: screening for TB, Carried out by IFN - gamma assay, tuberculin skin tests
what is MDR and XDR TB
multi drug resistant TB
resistant to rifampicin and isoniazid
resistant to flurorquinolomes
spontaneous mutation and inadequate treatment
