Week 7 - TB and Lung Cancer Flashcards
1
Q
Describe a primary TB infection
A
- Occurs on first exposure
- Primary focus = development of sub-pleural focus of tubercles following deposition of TB bacilli in the alveoli
- TB bacilli drain from the primary focus into the hilar lymph nodes
- Primary focus + draining hilar lymph nodes = primary complex
- Primary complex does not heal, but continues to progress and causes disease
- Most infections resolve with local scarring
- Most primary infections will heal with or without calcification of the primary complex
2
Q
Describe a post-primary TB infection
A
- Development of TB beyond the first few weeks
- Infection may progress throughout the body (Miliary spread)
- – May resolve spontaneously or develop into localised infection
- Due to reactivation of latent TB
3
Q
Describe latent TB infection
A
- In the majority of cases, before healing occurs in primary infection, some TB bacilli enter the blood stream
- Haematogenous spread occurs, resulting in the seeding of tubercle bacilli to other parts of the lung as well as other organs (extra-pulmonary sites)
- With the development of cell-mediated immunity the infection is contained
- Primary complex heals, but a small number of organisms remain viable in the lungs/other organs, such as:
- – Larynx
- – Lymph nodes
- – Pleura
- – Brain
- – Kidneys
- – Bones and joints
- This state, where TB bacilli can persist within the human host, without causing disease, for years or until death due to other causes, is known as latent TB
- The person remains well, but the potential for reactivation at any site is always present
- – Reactivation usually occurs when the patient’s immune mechanisms wane or fail
- Characterised by a positive tuberculin skin test
- – Demonstrates a type IV hypersensitivity reaction to proteins derived from mycobacteria
4
Q
Describe the host response to TB infection
A
- Mycobacterium TB is ingested by macrophages
- It escapes from the phagolysosome to multiply in the cytoplasm
- At the same time it provokes an immune response, stimulating the release of of IL-12
- – This in turn drives the release of IFN-γ and TNF-α from NK and CD4 cells
- – These cytokines activate and recruit more macrophages to the site of infection, resulting in the formation of granulomas
5
Q
What are the primary changes in TB?
A
- Few symptoms
- Lymph nodes may become enlarged in young people
6
Q
What are the post-primary changes in TB?
A
Classical presentation:
- Cough
- Fevers
- Weight loss and general debility
7
Q
How do you diagnose TB?
A
- Usually suggested by findings of compatible x-ray changes during investigation of patients with:
— Persistent cough
— Haemoptysis
— Unresolved pneumonia
— Nonspecific symptoms
• E.g. fever, weight loss - Plus the identification of the tubercle bacillus in the appropriate body fluid by direct smear and subsequent culture
— Important to isolate the organism and determine its susceptibility to drugs
8
Q
What is the classical presentation of TB?
A
- Cough – not always productive
- Often with fevers towards the end of the day
- Weight loss and general debility
9
Q
What would you expect to see on a chest x-ray for TB?
A
- Shadowing
- Cavities
- Consolidation
- Calcification
- Cardiomegaly
- Miliary seeds
10
Q
What are some symptoms and signs of TB?
A
Symptoms: - Fever - Night sweats - Weight loss and anorexia - Tiredness and malaise - Cough - Haemoptysis occasionally - Breathlessness if pleural effusion Signs: - Non-specific --- Fever --- Weight loss - Often no chest signs, despite a chest x-ray abnormality - Maybe crackles in affected area - In extensive disease: --- Signs of cavitation --- Fibrosis - If pleural involvement, there are typical signs of effusion
11
Q
Describe pleural TB
A
- More common in males, there are 2 mechanisms of pleural involvement
- There is almost always some pulmonary disease present:
— Hypersensitivity response in primary infection
— TB empyema with ruptured cavity
• Has a tendency to burrow through the chest wall
12
Q
Describe lymph node TB
A
- More common in children, women and Asians
- It is often painless and occurs most commonly in the neck
13
Q
Describe osteo-articular disease
A
TB burrows into bone
- Tuberculous spondylitis
- – Most common form of osteoarticular TB
- – Starts in sub-chondral bone and spread to vertebral bodies and joint space, before following the longitudinal ligaments, anterior and posterior to the spine
- – Mainly occurs in the lower thoracic and lumbar spine, but can be very high
- – Paraplegia and quadriplegia occurs in 25% of cases
- Poncet’s disease:
- – Aseptic polyarthritis
- – Knees, ankles and elbows
14
Q
Describe miliary TB
A
- Bacilli spreading through the bloodstream
- Either during primary infection or as reactivation
- Lungs are always involved
- – Even spread throughout both lungs, as it is in the blood
- – Many visible through the lungs on an X-ray
- Headaches suggest meningeal involvement
- Few respiratory symptoms
- Ascites may be present
- Retinal involvement in children
15
Q
How do you manage TB?
A
- Multi-drug therapy for 2 months:
- – Rifampicin
- – Isoniazid
- – Pyrazinamide
- – Ethambutol
- After 2 months, 2 of them are dropped
- – RIfampicin and isoniazid are continued for another 4 months
- Multiple drugs are used in an attempt to combat resistance
- Vitamin D
- Surgery
- – Rare
- Can be problems with compliance since there are lots of different pills to take for quite a long time
- – Can monitor it
- Need to do a follow up culture
