TB and pleural infection

Question 1

What happens after exposure to TB?

Answer 1

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

Question 2

What percentage of people exposed to the pathogen will develop TB?

Answer 2

90% will remain well (up to 50% will clear TB spontaenously)
10% lifetime risk of disease:
5% primary TB
5% reactivation of latent disease

Question 3

What are the clinical features of TB?

Answer 3

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

Question 4

What is spinal TB?

Answer 4

Infection starts in one disk and then spreads into the two adjacent vertebrae with subsequent anterior collapse of that segment of the spine

Question 5

What is a cold abscess?

Answer 5

A collection of pus without the pain and acute inflammation seen in a conventional abscess

Question 6

What is a ZN stain?

Answer 6

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

Question 7

Why is PCR used?

Answer 7

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

Question 8

How is histology used to diagnose TB?

Answer 8

Multinucleate giant cell granulomas
Caseating necrosis
Sometimes visible mycobacteria

Question 9

How can radiology be used to diagnose TB?

Answer 9

Upper lobe predominance
Cavity formation
Scarring and shrinkage
Heals with calcification

Question 10

What is miliary TB?

Answer 10

Massive seeding of mycobacteria through the bloodstream gives miliary TB. If left untreated it can be rapidly fatal

Question 11

How can combination therapy be used to treat TB?

Answer 11

Two months of: Rifampicin, Isoniazid, Pyrazinamide, Ethumbutol
Then four months of: Rifampicin and Isoniazid

Question 12

What does rifampicin do to your urine?

Answer 12

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

Question 13

What are the different types of drug-resistant TB?

Answer 13

Single agent - Commonly isoniazid
Multi-drug resistant MDR: Rifampicin and isoniazid
Extensive Drug Resistant XDR: MDR and quinolone and injectable

Question 14

What is latent TB?

Answer 14

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

Question 15

How is latent TB diagnosed?

Answer 15

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

Question 16

What are some tests that can be done to test for previous exposure to TB?

Answer 16

Interferon Gamma Release Assay - blood test

Mantoux (tuberculin) test - skin test that detects previous exposure to TB but also the vaccine BCG

Question 17

What are the drawbacks to the mantoux skin test?

Answer 17

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

Question 18

How do the TST and IGRA compare in diagnoisng TB?

Answer 18

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

Question 19

How is latent TB managed?

Answer 19

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

Question 20

What is anti-TNF therapy prescribed for?

Answer 20

Rheumatoid arthritis
Crohn’s disease
Psoriasis
Ankylosing Spondylitis - inflammatory condition that affects the joints in your spine

Question 21

Why are antibiotics indicated for latent TB when giving anti-TNF therapy?

Answer 21

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

Question 22

How can TB be prevented?

Answer 22

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

Question 23

What is the BCG immunisation?

Answer 23

Attenuated strain of mycobacterium bovis
Intradermal injection
Most effective in neonates of high risk families

Question 24

What is the link between HIV and TB?

Answer 24

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

Question 25

What are the risk factors to developing a pleural infection?

Answer 25

Diabetes mellitus
Immunosupression including corticosteroids
Gastro-oesophageal reflux
Alcohol misuse
IV drug abuse
Many patients however have no apparent risk factors

Question 26

What are the different types of pleural effusion?

Answer 26

Simple parapneumonic effusion
Complicated paranpneumonic effusion
Empyema
Quickly sample pleural fluid to identify parapneumonic effusions that require urgent tube drainage

Question 27

What are the signs of a complicated effusion?

Answer 27

Positive gram stain
pH <7.2 
Low glucose 
Septations
Loculations

Question 28

What are the signs of a simple effusion?

Answer 28

May be treated with antibiotics but drainage may be needed later on

Question 29

What is the management of a pleural infection?

Answer 29

Antibiotics often for several weeks
Drain effusion if large 
Surgery if persistent sepsis 
Nutrition 
VTE prophylaxis (venous thromboembolism)