Tuberculosis

Question 1

What are the risk factors for acquiring TB?

Answer 1

HIV, low socioeconomic status/poverty, underweight, DM, cirrhosis, past gastric surgery, coeliac disease

Question 2

What is the presentation of TB?

Answer 2

• Initial infection usually goes unnoticed—latent TB infection (LTBI).
• Approximately 10% of those with LTBI will eventually progress to active disease, and half will do so in the first 2 to 3 years following infection. Immunocompromised patients (e.g. HIV infection, diabetes mellitus) are at higher risk for developing active TB.
• Pulmonary TB: Common symptoms are prolonged cough (> 3 weeks), chest pain and haemoptysis.
• Patients with miliary TB may have minimal respiratory symptoms and present with systemic complaints.
• Extrapulmonary TB: Lymphadenitis (especially cervical), pleural effusion, osteomyelitis, meningitis or gastrointestinal involvement.
• Patients often have associated fever, night sweats, loss of appetite, loss of weight and fatigue.

Question 3

What are the investigations needed to be done for actuve TB?

Answer 3

Acid fast bacilli (AFB) smear and TB culture of sputum and other pathological specimens such as pleural fluid, CSF, urine and pus. 2 consecutive sputum specimens should be obtained for both microscopy and mycobacterial cultures, 1 being an early morning collection. children/stroke patients, gastric lavage or sputum induction may be useful (because difficult to obtain sputum specimens)

Acid fast bacilli (AFB) smear
- Auramine rhodamine (AR) stain is more sensitive than Ziehl-Neelsen (ZN), but ZN spec > AR spec)

Nucleic acid amplification tests (NAAT): do not obviate the need for TB culture as these tests do not provide information on the drug susceptibility pattern of the organism. The NAATs are not sufficiently sensitive for a negative result to exclude TB in smear-negative sputum samples

Mycobacterial c/s

• Middlebrook 7H12 or 7H9 broth (egg media)
• Lowenstein-Jensen (albumin media)
• Drug sensitivity –> Check if MDR TB!
• Note slow doubling time; 6 weeks may be required to grow Mycobacteria

CXR/CT chest

• Classically apical/sub-apical infiltrates, cavitation
• Normal CXR, or any pattern may be seen -> e.g. pulmonary nodules, diffuse infiltrates
• Ghon focus: healed lesions w/ fibrosis and calcification (commonly in primary PTB)
• Ghon complex: Ghon focus + mediastinal/hilar lymphadenopathy
• Primary Ranke complex: Ghon focus + spread to regional LN causing granulomatous lymphangitis and lymphadenitis

HIV testing should be performed for all patients.
Screening for diabetes mellitus is strongly recommended.

Question 4

What are the complications of TB?

Answer 4

• Major haemoptysis
• Pneumothorax
• Long-term bronchiectasis

Question 5

What is the management of TB?

Answer 5

Directly observed therapy (DOT)

Uncomplicated, drug-susceptible pulmonary TB is treated with 4 drugs (rifampicin, isoniazid, pyrazinamide and ethambutol) in the intensive phase of 2 months, followed by rifampicin and isoniazid in the continuation phase of four months. It is recommended that the treatment duration be extended by three months in persons with cavitary disease and whose sputum cultures remain positive at two months of treatment..

Initiating treatment using a quinolone as a first-line drug is not a standard practice.

There should be an index of suspicion for the possibility of drug-resistant TB in patients who were previously treated, who fail treatment, who are known contacts of MDRTB cases, or who come from countries with high prevalence of TB drug resistance.

Patients with TB at certain sites (e.g. meningitis and skeletal TB) would require a longer course of treatment. Persons with MDR-TB require to be treated with multiple second-line drugs for 18-20 months.

Question 6

What is the pathophysiology of TB?

Answer 6

• Hypervirulent strains (Beijing strain)
• Mycolic acid cell wall 🡪 activates Langerhans cells, lymphocytes, neutrophils
• Persist in macrophages 🡪 epithelioid granuloma with central caseation necrosis
• Primary versus latent infection (1:9) in immunocompetent, with risk of reactivation in latter

Question 7

What are the investigations for latent TB?

Answer 7

• Currently, there is no gold standard diagnostic test for latent TB infection (LTBI)
• LTBI is inferred from a positive tuberculin skin test (TST, aka Mantoux test) or interferon-g release assay (IGRA) in the absence of clinical and radiological evidence of active TB
• TST and IGRA reflect immuno-sensitisation to MTB, but does not distinguish between persistent MTB infection (i.e. presence of viable bacilli) and immunological memory of an infection that has been eradicated
• Testing should be targeted towards individuals with risk factors for progression to active disease (e.g. recent close exposure to an infectious TB case, immunocompromised state, and other medical conditions) who would benefit from Latent Tuberculosis Infection treatmen