Tuberculosis Flashcards
What organisms cause tuberculosis?
There are 4 (the Mycobacterium tuberculosis complex):
- M. tuberculosis
- M. bovis
- M. africanum
- M. microti
What sort of bacteria are the tuberculosis causative organisms?
Obligate aerobes
Facultative intracellular pathogens
What sort of cells does tuberculosis generally infect?
Mononuclear phagocytes
How is tuberculosis spread?
Airborne disease spread by respiratory droplets.
What is primary tuberculosis?
First infection with MTb.
Outline the pathogenesis of primary Tb.
- Inhaled into lung
- Alveolar marophages ingest bacteria
- Bacilli proliferate inside M0 trigger release of Neutrophil chemoattractants; inflamm infiltrate in lung and hilar LN
- M0 present antigen to T cells
- Delayed type hypersensitivity –> tissue necrosis and granuloma formation.
Describe the structure of a granuloma.
Central area of necrotic material (caseation), surrounded by epithelioid cells and Langhan’s giant cells with multiple nuclei.
Lymphocytes present
Varying degree of fibrosis
What happens after a granuloma heals?
Granuloma becomes calcified.
Some calcified nodules contain bacteria - these are contained by the immune system (and the hypoxic, acidic environment of the granuloma). May be dormant for many years.
How does the Ghon focus appear on CXR?
Small calcified nodule often within the upper parts of the lower lobes or the lower parts of the upper lobes, seen in the midzone.
What is the primary complex of Ranke?
A focus within the regional draining lymph node.
What is latent Tb?
Most infected people develop cell-mediated immunity to bacteria = latent infection.
What are the clinical features of pulmonary TB?
- Productive cough
- +/- haemoptysis
- Systemic: LOW, fever, sweats (EOD and night)
- If involving larynx: hoarse voice and cough
- If involving pleura: pleuritic chest pain
What are the clinical features of lymph node TB?
Extrathoracic nodes more common (than intrath or mediastinal).
Firm, non-tender enlargement of a cervical or supraclavicular node.
Node becomes necrotic centrally > can liquefy > becomes fluctuant.
What are the clinical features of miliary TB?
Haematogenous spread to multiple sites inc CNS (20%).
- Systemic upset, resp symptoms
- +/- liver and splenic microabscesses
- Deranged LFTs, or cholestasis and GI symptoms
- CXR shows miliary seed like presentation
What are the appropriate diagnostic investigations in pulonary, pleural and laryngeal TB?
Smear and culture of:
- Sputum (>2 samples increases diagnostic yield)
- Bronchoalveolar lavage fluid if cough unproductive
- Aspiration of pleural fluid and pleural biopsy
- Gastric aspirates (paediatric disease)
- Nasoendoscopic or bronchoscopic exam/biopsy/smear of vocal cords in laryngeal disease.
What are the Dx Ix in miliary TB?
- blood cultures
- bronchoalveolar lavage fluid (usually smear negative, culture positive)
- LP in all cases to assess CNS involvement
What are the characteristics of LP fluid in CNS TB?
CSF protein may be very high (>2-3g/L)
CSF glucose
What are the Ix in LN TB?
Histocytopathological examination, culture and smear of:
- FNA or biopsy of LN under radiological guidance
- Mediastinal nodal sampling (EBUS, mediastinostomy)
What is the duration of treatment for TB?
6 months, excluding CNS TB which requires 12 months.
In which forms of TB are corticosteroids used?
Corticosteroids used in CNS and pericardial TB to reduce long term complications.
AEx rifampicin?
- Induces liver enzymes
- Liver enzyme induction –> reduces efficacy other Rx
- Thrombocytopaenia reported
- Stains body secretions pink
- OCP ineffective
AEx isoniazid?
Very few
- High doses > polyneuropathy due to B6 deficiency (interferes with pyridoxal phosphate)
- Occasionally rash
AEx pyrazinamide?
- May cause hepatic toxicity (rare).
- Reduces renal excretion of urate > may precipitate gout
AEx ethambutol?
Dose related optic retrobulbar neuritis: presents with green colour blindness, reduction in visual acuity and central scotoma
