Tuberculosis Flashcards
How is TB contracted?
- airborne droplet spread
- that is then inhaled
- deposited in the terminal airspaces
- macrophages engulf bacilli
- bacilli replicate within endosomes
- transported to the regional lymph node where it is
- killed
- multiplies → primary TB
- Dormant → asymptomatic
- proliferate after a period of latency → reactivation disease
What is the pathology of TB under a microscope?
- Granulomatous inflammation
- Rim of lymphocytes
- Fibroblasts
- Central infected macrophages (giant cells)
- Central necrosis – caseation
- Secretion of cytokines (IFNγ) – activate macrophages to kill bacteria
- AFBs in granulomas
What lab tests are done to identify TB?
- Ziehl- Neelsen stain
- shows bright red bacilli on blue background
- Auramine-rhodamine stain
- Fluorescent microscopy
Who is at risk of transmitting TB?
- close contact infectious cases, smear +ve
- those from a high incidence country or travelling to those areas frequently
- Those who are immunodeficient
- HIV
- Chemotherapy
- Steriods
- Nutritional deficiency (vit D)
- Diabetes
- end-stage renal cancer
- Lifestyle factors
- genetic susceptibilities
Describe the disease progression of TB
- Primary TB: bacilli overcome immune system soon after the initial an infection
- Latent infection (majority of cases): risk of reactivation increases with immunosupression
What are the symptoms and diagnosis of Pulmonary TB?
Accounts for the majority of TB cases: 55%, cavitatory disease and is more infectious
- cough
- chest pain
- weight loss
- hemoptysis
- Chest imaging
- Sputum/BAL test
What can be seen in a CXR with TB?
- Hilar lymphadenopathy: a biopsy would be taken
What is TB lymphadenitis?
- TB in the lymph nodes
- can get worse with treatment
- can form sinus tracts with chronic discharge
- presents with cold abscess formation
Describe Disseminated/ miliary TB
Symptoms
- fevers
- sweats
- weight loss
- malaise
- GI or CNS symptoms in 20% of cases
- Abdo pain
- diarrhoea
- hepatomegaly in 50%
- headache or confusion
What controls are in place for TB?
- Government global policy
- Consider the diagnosis!
- Early diagnosis AND treatment (even if negative cultures/smear)
- Isolate if appropriate (? Resp/Laryngeal TB)
- Optimal treatment
- Optimal adherence (DOT/VOT/Section)
- Contact tracing
Prevention
How is active TB diagnosed?
- identify infected area CXR
- isolate the organism
- obtain information regarding susceptibility to antibacterials
Explain how the Mantoux test is used to diagnose a latent TB infection. Alternatives?
- the Mantoux, tuberculin skin test
- relies on circulating memory T-cells
- ability to mount a delayed hypersensitivity reaction
- cross-reactive with other mycobacterial antigens,
- maybe falsely negative in severely ill or immunosuppressed individuals
- Interferon Gamma Release Assays can be used instead
- more specific
- correlates better with the degree of exposure
What is this a CXR of
Miliary TB
What other sites can TB be found?
more common in those from Asian heritages that ar non-UK born, usually reactivated
- Lymph nodes
- CNS
- Bone (Pott’s disease of the spine)
- Genitourinary system
- GI tract
- Disseminated/miliary
What are the first-line drugs and treatment for TB?
2 months on: (initial phase)
- Isoniazid
- Rifampicin
- Pyrazinamide
- Ethambutol
4 months on: (continuous phase, extended for 10 months if CNS involved)
- Isoniazid and Rifampicin
