TB and pleural infection Flashcards
What happens after exposure to TB?
In latent infections, the mycobacterium tubercolusis is inhaled and then migrates to the lymph nodes for T cell priming and forms a granuloma
In active TB, the same happens but the granuloma will “burst” from the granuloma and the infection will spread systemically
What percentage of people exposed to the pathogen will develop TB?
90% will remain well (up to 50% will clear TB spontaenously)
10% lifetime risk of disease:
5% primary TB
5% reactivation of latent disease
What are the clinical features of TB?
Subacute disease of gradual onset
General: Weight loss, malaise and night sweats Respiratory: Cough, haemoptysis, breathlessness, upper zone crackles
Meningeal: Headache, drowsy, fits
GI: Pain, bowel obstruction, perforation, peritonitis
Spinal: Pain, deformity, paraplegia
Lymphadenopathy
Cold abscess
Pericardial: Tamponade
Renal: Renal failure
Septic arthritis: Cold monoarthritis of large joints
Ardenal: Hypoadrenalism
What is spinal TB?
Infection starts in one disk and then spreads into the two adjacent vertebrae with subsequent anterior collapse of that segment of the spine
What is a cold abscess?
A collection of pus without the pain and acute inflammation seen in a conventional abscess
What is a ZN stain?
The whole slide is stained pink then washed with acid and alcohol, this removes the stain from everything except mycobacteria. The mycobacteria hang on to the stain due to the high wax content of their cell wall. The final step is to add a blue counter stain which helps to visualise the pink mycobacteria
Why is PCR used?
It only takes 2 hours and it picks up all of the smear positive cases and most of the culture positive cases. It also says if the organism is resistant to rifampicin
How is histology used to diagnose TB?
Multinucleate giant cell granulomas
Caseating necrosis
Sometimes visible mycobacteria
How can radiology be used to diagnose TB?
Upper lobe predominance
Cavity formation
Scarring and shrinkage
Heals with calcification
What is miliary TB?
Massive seeding of mycobacteria through the bloodstream gives miliary TB. If left untreated it can be rapidly fatal
How can combination therapy be used to treat TB?
Two months of: Rifampicin, Isoniazid, Pyrazinamide, Ethumbutol
Then four months of: Rifampicin and Isoniazid
What does rifampicin do to your urine?
It colours all urine and bodily fluids orange. It is also a potent inducer of cytochrome enzymes and causes the rapid breakdwon of all steroid molecules including hormonal contraception
What are the different types of drug-resistant TB?
Single agent - Commonly isoniazid
Multi-drug resistant MDR: Rifampicin and isoniazid
Extensive Drug Resistant XDR: MDR and quinolone and injectable
What is latent TB?
Symptom free
Culture negative
Balance between the organism and your immune system
It is though that between a quarter and a third of the world’s population has latent TB
How is latent TB diagnosed?
There is no evidence of active TB this incules: symptoms, CXR and culture
There is however evidence of previous TB infection that includes calcifications of CXR with exposure to a high prevalance area
What are some tests that can be done to test for previous exposure to TB?
Interferon Gamma Release Assay - blood test
Mantoux (tuberculin) test - skin test that detects previous exposure to TB but also the vaccine BCG
What are the drawbacks to the mantoux skin test?
You need 2 visits, an intradermal injection and can give a false positive for BCG Cannot distHinguish between: Latent TB Cured TB Active TB BCG
How do the TST and IGRA compare in diagnoisng TB?
TST: 2 visits, operator dependent, false negative and positives, type 4 hypersensitivity recation (relies on the patients immune system to do the assay)
IGRA: 1 visit, lab environment, high sensitivity, ignores BCG
How is latent TB managed?
Can be ignored or treated
However if anti-TNF drugs are needing to be prescribed for another condition, the TB needs to be treated with 6 months of isoniazid or 3 months of rifampicin and isoniazis
What is anti-TNF therapy prescribed for?
Rheumatoid arthritis
Crohn’s disease
Psoriasis
Ankylosing Spondylitis - inflammatory condition that affects the joints in your spine
Why are antibiotics indicated for latent TB when giving anti-TNF therapy?
There is a 5 fold increase in reactivation of TB when giving anti-TNF therapy
Usually within the first 12 weeks and will have an atypical presentation
How can TB be prevented?
Contact tracing to identify further cases
Screening of high risk subgroups (esp migrants and prior to immunosuppressive agents)
Isolation of infectious cases
BCG immunisation
Social measures - housing and nutrition
TB is a notifiable disease
What is the BCG immunisation?
Attenuated strain of mycobacterium bovis
Intradermal injection
Most effective in neonates of high risk families
What is the link between HIV and TB?
12% of all new active TB cases and 25% of all TB-related deaths occur in HIV positive individuals
All TB cases should be offered an HIV test
All HIV cases should be offered a CXR
Steroids and other immunosuppressant drugs can reactivate latent TB
What are the risk factors to developing a pleural infection?
Diabetes mellitus
Immunosupression including corticosteroids
Gastro-oesophageal reflux
Alcohol misuse
IV drug abuse
Many patients however have no apparent risk factors
What are the different types of pleural effusion?
Simple parapneumonic effusion
Complicated paranpneumonic effusion
Empyema
Quickly sample pleural fluid to identify parapneumonic effusions that require urgent tube drainage
What are the signs of a complicated effusion?
Positive gram stain pH <7.2 Low glucose Septations Loculations
What are the signs of a simple effusion?
May be treated with antibiotics but drainage may be needed later on
What is the management of a pleural infection?
Antibiotics often for several weeks Drain effusion if large Surgery if persistent sepsis Nutrition VTE prophylaxis (venous thromboembolism)
