tuberculosis Flashcards
what is the pathogenesis of TB?
- 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)
key characteristics of the TB bacteria?
- 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
how do you identify the granulatomatous inflammation?
- rim of lymphocytes
- fibroblasts
- central infected macrophages (giant cells)
- central necrosis: caseation
- secretion of cytokines: active macrophages to kill bacteria
- AFBs in granulomas
what increases the transmission risk of TB?
- 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
what are the principles of active TB?
- identify the infected area
- isolate the organism
- obtain information regarding susceptibility to antibacterial
what are the principles of latent TB?
identify immune response to TB proteins to TB-specific antigens
the tuberculosis skin test (Mantoux)
- 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
interferon gamma release assays
- 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
what are the clinical features of pulmonary TB?
- cough
- haemoptysis
- chest pain
- weight loss
- fever
- night sweats
how do you diagnose pulmonary TB?
- chest imaging
- sputum/BAL
where are the sites of extrapulmonary disease?
- lymph nodes
- CNS
- bone
- genitourinary system
- GI tract
- disseminated/miliary
what happens with TB lymphadenitis?
- often gets worse on treatment: paradoxical reaction
- can form sinus tracts and chronic discharge
- cold abscess formation
what happens with disseminated/miliary TB?
- 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%
what happens with genitourinary TB?
- kidney/bladder/pelvic involvement
- pus in urine but repeatedly negative standard cultures
what happens with TB enteritis?
- Ileo-caecal commonest
- weight loss, diarrhoea, blood in stools
what happens with TB of eyes?
- any part of the eyes
- more common than we think
what happens with CNS TB?
- TB meningitis
- TB arachnoiditis
- tuberculoma
- spinal cord compression
how do you control TB?
- government global policy
- consider the diagnosis kiss
- early diagnosis AND treatment
- optimal treatment and adherence
- contract tracing
- prevention: BCG vaccine
- latent treatment programs: prevent TB become active
what is the standard treatment for TB is a minimum of 6 months?
- 2 months (initial phase): Isoniazid, Rifampicin, Pyrazinamide and Ethambutol: known as quadruple therapy
FOLLOWED BY - 4 months (continuation phase): Isoniazad, Rifampici known as the standard dual therapy
- TB treatment is taken all together on an empty stomach 1 hour before breakfast; compliance is essential for cute
what happens to treatment if there is central nervous system involvement with TB?
the continuation phase of treatment is extended to 10 months making a 12 month treatment plan
what are the side effects of pyrazinamide?
hepatoxicity, joint mains and N&V
what are the side effects of rifamicin?
hepatoxicity, reddish colour to the urine
what are the side effects of isoniazid?
hepatoxicity, fever, peripheral neuropathy and optic neuritis
what are the side effects of ethambutol?
peripheral neuropathy, optic neuropathy and gout
what are the side effects of all TB drugs?
nausea and skin rashes
