tuberculosis Flashcards
1
Q
what is the pathogenesis of TB?
A
- airborne droplet spread
- inhaled: deposited in terminal airspaces
- macrophages ingest bacilli: replicate within endosome
- transported to regional lymph node: killed, multiply (primary TB), dormant (asymptomatic), proliferate after a period of latency (reactivation disease)
2
Q
key characteristics of the TB bacteria?
A
- aerobic bacillus
- divides ever 16-20 hours (slow)
- cell wall, but lacks phospholipid outer membrane
- doesn’t stain strongly with gram stain (weakly positive)
- retains stains after treatment with acid: acid fast bacillus
3
Q
how do you identify the granulatomatous inflammation?
A
- rim of lymphocytes
- fibroblasts
- central infected macrophages (giant cells)
- central necrosis: caseation
- secretion of cytokines: active macrophages to kill bacteria
- AFBs in granulomas
4
Q
what increases the transmission risk of TB?
A
- close contacts of infectious cases (smear +)
- contract with high risk groups: high incidence country. frequent travel to high incidence areas
- immune deficiency: HIV, steroids, chemotherapy, nutritional deficiency, diabetes, end stage renal failure
- lifestyle factors: drug/alcohol misuse, homelessness/hostels/overcrowding, prison inmates
- genetic susceptibility
5
Q
what are the principles of active TB?
A
- identify the infected area
- isolate the organism
- obtain information regarding susceptibility to antibacterial
6
Q
what are the principles of latent TB?
A
identify immune response to TB proteins to TB-specific antigens
7
Q
the tuberculosis skin test (Mantoux)
A
- circulating T-lymphocytes
- ability to mount a delayed hypersensitivity reaction
- cross reactive with other mycobacterial antigens so non-specific
- may be falsely negative severely ill or immunosuppressed individuals
8
Q
interferon gamma release assays
A
- elispot/elisa: enzyme-linked immunological assay of release of interferon-gamma in whole blood following stimulation by specific TB antigen
- more specific than Mantoux
- correlates better with degree of exposure than Mantoux
- does not differentiate between latent infection and disease
- T-spot TB
- quantiferon gold
9
Q
what are the clinical features of pulmonary TB?
A
- cough
- haemoptysis
- chest pain
- weight loss
- fever
- night sweats
10
Q
how do you diagnose pulmonary TB?
A
- chest imaging
- sputum/BAL
11
Q
where are the sites of extrapulmonary disease?
A
- lymph nodes
- CNS
- bone
- genitourinary system
- GI tract
- disseminated/miliary
12
Q
what happens with TB lymphadenitis?
A
- often gets worse on treatment: paradoxical reaction
- can form sinus tracts and chronic discharge
- cold abscess formation
13
Q
what happens with disseminated/miliary TB?
A
- fevers, sweats, weight loss and malaise
- respiratory symptoms in majority
- GI or CNS symptoms in 20%: abdominal pain, diarrhoea, abnormal LFTs, hepatomegaly in 50%, headache or confusion; altered mental state 20%
14
Q
what happens with genitourinary TB?
A
- kidney/bladder/pelvic involvement
- pus in urine but repeatedly negative standard cultures
15
Q
what happens with TB enteritis?
A
- Ileo-caecal commonest
- weight loss, diarrhoea, blood in stools
