TB

Question 1

Definition of TB

Answer 1

Is a chronic infectious disease, that can affect multiple organs, caused by MYCOBACTERIUM TUBERCULOSIS
• Is a granulomatous disease

Question 2

Aetiology of TB

Answer 2

• In many patients, M tuberculosis becomes dormant before it progresses to active TB
• Transmission occurs from individuals infected with pulmonary TB
◦ The infection would result from inhalation of infected aerosolised particles

-Predominantly affects upper lobes of lung

Question 3

Risk factors for TB

Answer 3

• Exposure to infection
• Birth/travel to endemic country
• HIV infected
• Homeless
• IV drug users
• Smokers
• Silicosis
• Immunocompromised individuals

Question 4

Pathophysiology of TB

Answer 4

When infection occurs due to inhalation of infected aerosols (droplet nuclei), three things can occur:
• Successful clearance of TB:
•
• Progression to primary active disease:
◦ The patient would be infectious and the TB would be transmissible and would display symptoms
◦ Active disease can either occur primarily or through reactivation of latent disease

• Latent TB:
• More common
• The TB would be contained in GRANULOMAS (caseating granulomas), which are made up of T cells and macrophages and a necrotic centre (caseous centre) that contains the M tuberculosis
• These patients would be non-infectious and the majority would have a normal chest x-ray and be tuberculin skin test positive
◦ HOWEVER, there is a chance of REACTIVATION of the infection.
◦ The risk can be increased due to HIV, immunocompromised conditions and immunosuppressing medicines (e.g steroids), aging, organ transplantation, illicit drug use

Question 5

History and Examination of TB

Answer 5

• Cough: duration of 2-3 weeks. Initially dry and later productive
• Fever: low-grade fever
• Anorexia
• Weight loss
• Malaise
• Night sweats

Extra-pulmonary symptoms:
• Clubbing: in long standing disease
• Erythema nodosum and erythema induratum: painful raised erythematous nodules over the pretibial region (anterior aspect of shin or on calves
• Lupus vulgaris:
• Meningitis
• Pott’s disease: osteomyelitis of the spine due to TB
• Addison’s disease: TB is the most common cause of this worldwide
• Pleural effusion

Question 6

Investigations for TB

Answer 6

Active TB:
• Sputum MCS with acid-fast bacilli (AFB) staining: most common is Ziehl-Neelson
• FBC: would show leukocytosis
• Chest X ray:
• First line investigation
• Would see fibronodular opacities in upper lobes can be cavitating
• May see bi-hilar lymphadenopathy

Latent TB: can also be used to screen close contacts
• Tuberculin skin test (Mantoux test): inject tuberculin protein and see if size of skin changes (increase indicates positive test for TB), affected by BCG vaccine
• Interferon-gamma release assays: take blood sample and expose it to tuberculin protein. They then see how much interferon gamma is released

Question 7

Treatment for TB

Answer 7

ACTIVE TB:
1) Intensive phase therapy: 4 antibiotics
R- rifampicin:
• Would give for 2 months and then another 4 months (6 months total)
• Can lead to red-orange body secretions

I- isoniazid:
• Give for 2 months and then further 4 months (6 months total)
• Can cause peripheral neuropathy
• Can give pyridoxine to reduce risk of this

P- pyrazinamide:
• Give for first 2 months
• Can lead to hyperuricaemia

E- ethambutol:
• Give for first 2 months
• Can lead to optic neuritis

For latent TB: can give rifampicin and isoniazid

Question 8

Prevention and prognosis of TB

Answer 8

BCG vaccine
If infected, avoid contact with others . Close contacts should be screened
Active TB is a notifiable disease

Prognosis is good with effective treatment and low risk of complications
However, mortality is 50% without treatment