Tuberculosis (RESP) Flashcards
Define TB.
An infectious, chronic, granulomatous disease
Which organism is TB caused by?
Mycobacterium tuberculosis
What body parts does TB affect?
Typically lungs (pulmonary TB) especially upper lobes, but can spread to any organ haematologically to cause extrapulmonary TB
Describe the disease progression from primary to secondary TB.
- Mycobacterium tuberculosis is dormant in many patients before it progresses to active TB
- primary TB is asymptomatic and occurs in immunocompetent individuals who are exposed to M. tuberculosis - this usually heals
- (initial infection may be pulmonary or rarely GI and is typically lower lobe initially)
- if host becomes immunocompromised, the initial infection may become reactivated into secondary TB
- miliary TB occurs if there is haematogenous dissemination of TB
What does accumulation of lymphocytes and macrophages cause in TB?
Accumulation of lymphocytes and macrophages in the initial phase –> formation of caseating granulomas (associated with necrosis) in the lungs and other organs –> develop latency
What is miliary TB?
Potentially fatal form of TB resulting from haematogenous dissemination of TB:
- kidneys causing sterile pyuria
- meningitis
- lumbar vertebrae –> Pott disease
- adrenals causing Addison’s
- liver causing hepatitis
- cervical lymph nodes
What are some risk factors for TB? (7)
- exposure to infection
- immunosuppression (diabetes, Cushing’s, steroid use)
- silicosis (form of lung fibrosis)
- HIV
- malignancy
- birth in an endemic country (India, Bangladesh, Sub-Saharan Africa)
- overcrowded areas
What are some examples of immunosuppression that increase TB risk? (3)
- diabetes
- Cushing’s
- steroid use
- (HIV)
Birth in which endemic countries increase TB risk? (3)
- India
- Bangladesh
- Sub-Saharan Africa
What are the clinical features of TB? (10)
- cough - productive (may have haemoptysis) + does not respond to conventional Abx therapy
- fever (chronic, fluctuating)
- weight loss
- night sweats
- SOB
- anorexia
- malaise
- pleuritic chest pain
- cervical lymphadenopathy + hilar lymphadenopathy
- Pott’s disease –> spread to bones
What are some clinical features of miliary TB? (4)
- fever
- weight loss
- meningitis
- yellow caseous tubercles spread to other organisms
What might you see on examination in TB? (6)
- chest exam may be normal in mild-moderate disease
- crackles
- bronchial breath sounds
- amphoric breath sounds (distant hollow breath sounds heard over cavities)
- clubbing (chronic disease)
- erythema nodosum, erythema induratum
What is the 1st-line investigation for TB?
Chest X-ray
What can CXR show for TB? (4)
- caseating granulomas - cavitating lesion in upper lobe
- consolidation / fibronodular opacities (in upper lobes usually) with or without cavitation
- bilateral hilar lymphadenopathy
- pleural effusion
What is the gold-standard diagnostic test for TB?
Sputum culture - most sensitive and specific test
What is a sputum acid-fast bacilli smear for TB?
- uses a Ziehl-Neelson stain or auramine stain
- acid fast bacillus +ve in TB
What test for another disease is offered to TB patients?
HIV test
What test is usually offered for contacts of infected TB patients and what does it screen for?
Mantoux test - screens for latent TB
(Purified protein derivative - PPD is injected intradermally, erythema occurs after 72h)
What can cause a false negative on the Mantoux test for latent TB? (4)
Immunosuppression:
- sarcoidosis
- steroid use
- lymphoma
- AIDS
- (age extremes, fever, hypoalbuminuria, anaemia)
What might FBC show in TB?
- leukocytosis
- anaemia seen in 10%
What is seen on histology in TB?
Caseating granulomas
What are some differential diagnoses for TB? (6)
- COVID-19
- community acquired pneumonia
- lung cancer
- non-tuberculous mycobacteria
- fungal infection
- sarcoidosis
What is the 1st line management for latent TB? (2)
- 3 months of isoniazid (with pyridoxine) and rifampicin
- OR 6 months of isoniazid (with pyridoxine)
What is the 1st line management for active TB? (4)
RIPE
- Rifampicin - 6 months
- Isoniazid - 6 months
- Pyrazinamide - 2 months
- Ethambutol - 2 months
How do we manage meningeal TB?
RIPE for prolonged period (at least 12 months) + steroids
What is a side effect of rifampicin (TB)?
Red/orange secretions - tears, urine
What are some side effects of isoniazid (TB)? (2)
- drug-induced lupus
- peripheral neuropathy - give pyridoxine (vitamin B6) to prevent
- e.g. pellagra (vitamin B3 deficiency) –> triad of dementia, diarrhoea and dermatitis –> death if untreated
- e.g. sideroblastic anaemia
What is a side effect of pyrazinamide (TB)?
Can cause gout due to hyperuricaemia
What is a side effect of ethambutol (TB)?
May cause optic neuritis (colour blindness, loss of visual acuity, and restriction of visual fields)
How do we manage meningeal TB?
RIPE for at least 12 months + steroids
What is a complication of TB treatment?
- immune reconstitution disease
- occurs typically 3-6 weeks after starting treatment
- often presents with enlarging lymph nodes
What needs to be done before giving BCG vaccine for TB?
Tuberculin skin test to check for past exposure to TB
What is MDR-TB?
TB that is resistant to 2+ first-line drugs including rifampicin and isoniazid - risk factors:
- previous drug treatment for TB
- incorrect dosages
- non-adherence
- travel to endemic regions
- social risk factors (alcohol, drugs, homeless, prison)
- exposure to patient with MDR-TB
- HIV seropositivity
What are some complications of TB? (7)
- transmission of TB
- immune reconstitution inflammatory syndrome
- ARDS
- pneumothorax
- haemoptysis
- bronchiectasis
- empyema
What is the mortality rate for TB without treatment?
> 50%
What is the prognosis like for treated TB?
In general, patients can expect to do well with minimal or no sequelae
