Tuberculosis (TB)

Question 1

What is TB and what organism is it caused by ?

Answer 1

It is an infection caused by Mycobacterium tuberculosis that most commonly affects the lungs

Question 2

What is the shape and gram stain of Mycobacterium tuberculosis?

Answer 2

Rod shaped gram positive bacillus

Question 3

How is TB spread?

Answer 3

Via aerosol route (coughing, sneezing)

Question 4

List the people most commonly affected by TB infection

Answer 4

• Ethnic minority groups (predominantly from South Asia and sub-Saharan Africa)
• Homeless patients, those with alcohol dependency and other drug misusers
• Malnutrition
• HIV-positive and other immunocompromised patients e.g. caused by immunosuppressive drugs
• Elderly patients: latent tuberculosis infection (LTBI) may reactivate in elderly patients.
• Children: young children are particularly susceptible to mycobacterial infection, due to their immature immune systems.

Question 5

Describe the pathogenesis of a primary TB infection

Answer 5

1. A non-immune host is exposed to M. tuberculosis (primary infection)
2. Host macrophages in the lung engulf the organisms and carry them to hilar lymph nodes in an attempt to control infection. The lung lesion plus affected lymph nodes is referred to as a Ghon complex.
3. Some organisms may disseminate via the lymphatics or bloodstream to distant sites. Small granulomas (with caseous necrosis in the centre) are formed around the body to contain the mycobacteria.
4. These may heal spontaneously by fibrosis and the bacteria are eliminated (in 80% of cases) or bacteria are encapsulated in a defensive barrier but persist in an otherwise healthy individual where the disease is considered dormant (latent).
5. Only a small proportion of patients progress to overt (active) TB.

Question 6

Describe the difference between active and latent TB infection

Answer 6

• Persons with latent TB infection do not feel sick and do not have any symptoms. They are infected with M. tuberculosis, but do not have TB disease. The only sign of TB infection is a positive reaction to the tuberculin skin test or TB blood test.
• Active TB is where TB bacteria overcome the defenses of the immune system and begin to multiply, resulting in the progression from latent TB infection to TB disease. Some people develop TB disease soon after infection, while others develop TB disease later when their immune system becomes weak.

Question 7

Is someone with latent TB infectious ?

Answer 7

• No - Persons with latent TB infection are not infectious and cannot spread TB infection to others.
• Only active TB is infectious

Question 8

Define what is meant by millary TB ?

Answer 8

This is when when the primary infection is not adequately contained and invades the bloodstream, resulting in severe disease.

Question 9

Describe what is meant by secondary TB infection and state where it most commonly occurs in the body and give examples of the causes for it

Answer 9

This is where someone with latent TB, has there TB reactived (to active TB), this is usually due to the host becoming immunocompromised.

Reactivation generally occurs in the apex of the lungs and may spread locally or to more distant sites. Possible causes of immunocomprise include:

• immunosuppressive drugs e.g. steroids
• HIV
• malnutrition

Question 10

Does TB only affect the lungs ?

Answer 10

No - The bacteria usually attack the lungs, but TB bacteria can attack any part of the body such as the kidney, spine, and brain.

Question 11

• The lungs remain the most common site for secondary TB.
• However extra-pulmonary infection may occur, list the areas which it may occur outside the lungs

Answer 11

• CNS (tuberculous meningitis - the most serious complication)
• Vertebral bodies (Pott’s disease)
• Cervical lymph nodes (scrofuloderma)
• Renal
• Gastrointestinal tract

Question 12

What are the general symptoms of TB ?

Answer 12

• Fatigue
• Malaise
• Fever
• Night sweats
• Weight loss & loss of appetite (anorexia)
• Failure to thrive

Question 13

What are the additional features alongisde the general symptoms of TB suggestive of pulmonary TB ?

Answer 13

• Cough + sputum
• Haemoptysis (can be massive)
• Pleurisy
• Pleural effusion

Question 14

What are the additional features alongisde the general symptoms of TB suggestive of Miliary TB ?

Answer 14

Severe disease with poor immune response can produce a picture like millet seeds over the CXR.

Question 15

What are the additional features alongisde the general symptoms of TB suggestive of genitourinary TB ?

Answer 15

• Often presents with sterile pyuria (pus in urine)
• Dysuria
• Polyuria
• Haematuria
• Loin/back pain

Question 16

What are the additional features alongisde the general symptoms of TB suggestive of spinal TB (potts disease) ?

Answer 16

• Severe back pain
• Arthritis
• Osteomyelitis and abscess formation (eg, loin mass or psoas abscess from spinal TB)
• Nerve root compression
• Isolated bone or joint lesions (monoarthritis).

Question 17

What are the additional features alongisde the general symptoms of TB suggestive of skin TB ?

Answer 17

Erythema nodosum (represents an early immunological response to infection), skin sinus formation (‘scrofuloderma’), erythema induratum

Question 18

What are the additional features alongisde the general symptoms of TB suggestive of GI TB ?

Answer 18

• Abdominal pain
• Bloating
• Obstruction
• Simulating appendicitis
• Occasionally ascites

Question 19

What are the additional features alongisde the general symptoms of TB suggestive of pericardial TB ?

Answer 19

Initially nonspecific; may be signs of pericardial effusion (pulsus paradoxus, elevated JVP) or constrictive pericarditis.

Question 20

What are the additional features alongisde the general symptoms of TB suggestive of TB meningitis ?

Answer 20

• Prodrome - Fever, headache, vomiting, abdo pain, drowsiness, meningism & delirium. Often worsens over 1-3weeks
• CNS signs - seizures, tremor, papilloedema, CNS palsies

Question 21

What is the treatment of CNS TB ?

Answer 21

Isoniazid (with pyridoxine), rifampicin, pyrazinamide and ethambutol (RIPE) for 2 months then isoniazid (with pyridoxine) and rifampicin for a further 10 months.

Question 22

Who do you screen for TB in/ screen for latent TB?

Answer 22

Those who have been in close contact of a person with pulmonary/laryngeal TB or have come to the country from a high TB incidence country

Question 23

How is latent TB diagnosed/ how do you screen for TB?

Answer 23

• 1st line = mantoux test
• 2nd line = if mantoux test positive, unclear, or patient is someone the test may be fasly negative in then do interferon-gamma testing to confirm

Question 24

Who may the mantoux screening test for TB be fasly negative in?

Answer 24

Those who have:

• Miliary TB
• Sarcoidosis
• HIV
• Lymphoma
• Are very young (<6months)

Question 25

What investigation should be done first for someone with suspected active pulmonary TB?

Answer 25

For pulmonary TB: * 1st line investigation = CXR (do further investigations if CXR appearance suggests TB)

Question 26

For someone who has CXR appearance of active pulmonary TB what samples should be obtained?

Answer 26

* Send 3 deep cough suptum samples (including 1 early morning sample) * (if not able to obtain these samples via the above method then obtain it using either gastric lavages or bronchoalveolar lavage)

Question 27

What investigations and samples should be obtained in someone with suspected non-pulmonary TB?

Answer 27

CXR + 3 deep cough suptum samples + biopsy or FNA of the site in question e.g. skin etc (apart from genitourinary site where you would also do x3 early morning urine samples)

Question 28

What tests are done on the samples obtained for suspected active TB?

Answer 28

Send samples for: 1. Culture 2. Microscopy (analysed using Ziehl-Neelsen stain & rapid direct microscopy for acid fast bacilli) 3. & histology (looking for presence of granulomata with central caseous necrosis)

Question 29

What is the treatment of active TB?

Answer 29

* 1st = Isoniazid (with pyridoxine), Rifampicin Pyrazinamide and Ethambutol **(RIPE)** for 2 months then * 2nd = Isoniazid (with pyridoxine) and rifampicin for a further 4 months.