Which organism causes TB and how would you stain it? How does transmission usually occur?
mycobacterium tuberculosis, stained with ziehl Nielsen. The transmission is usually by aerosol
Upon infection, how might you initially present?
Only 5% will go on to develop symptomatic TB, TB will initially enter and become dormant so the majority of hosts will be asymptomatic
What is the lifetime risk of those infected with TB developing the active disease?
10%
What happens during the initial infection?
The primary infection occurs on first exposure
1. M TB is phagocytosed by alveolar macrophages, but the bacterium prevents phagolysosomes from occurring so it isn’t initially killed. The bacterium can also grow intracellular
- These macrophages initiate the development of cell-mediated immunity produces lymphokines and infiltration of lymphocytes and activated macrophages with enhanced ability to kill TB
- A TB granuloma forms over 2-3 months
- Other cells react and deposit collagen fibres to enclose the infected macrophages within the tubercle, the infected cells in the centre die releasing M TB.
- This produces a caseous necrotic core surrounded by epithelioid macrophages, Langerhans giant cells and lymphocytes; Ghons focus
How is the ghons focus and ghons complex formed?
- Ghons focus: is formed from the caseous necrotic granuloma that is holding the initial TB infection, which may be in any lung zone
- If the infection is not controlled in that local site, TB bacilli drain from the ghons focus into the hilar lymph nodes. The primary ghons focus + draining (hilar) lymph nodes form the ghons complex/primary complex
How do most primary/ghons complexes heal?
Most heal with or without calcification.
What can happen right before healing of the ghons complex occurs and what is the inevitable result of this?
Before healing, some TB bacilli can enter the bloodstream (likely via lymph drainage to the venous system).
This hematogenous spread results in the seeding of the bacilli to other parts of the lung and other organs and may potentially be reactivated (latent TB)
When does secondary TB occur?
Post-primary/Secondary/Latent TB occurs when M tuberculosis ruptures from the tubercle and re-establishes the infection, this may happen either when
- The patient’s immune mechanisms wane or fail
- The patient is re-exposed
How can you detect latent TB, can it tell you everything about the disease?
A positive tuberculin skin test, as the test demonstrates a type IV hypersensitivity reaction to proteins derived from mycobacteria. However, it cannot indicate if the disease is active, merely just if there has been exposure to the organism
What is the risk of developing another active TB following resolution of the first?
5%
How does primary TB occur?
If the initial ghons complex was unable to heal
Where is post-primary TB often seen?
Often seen in the upper lung zones as the higher ventilation/perfusion ratio is believed to predispose reactivation of TB bacilli at these sites
Which individuals are at higher risk of developing TB?
- close contacts of persons suspected of TB
- elderly
- residents of high TB prevalent areas
- immunocompromised individuals
- patients with a history of poorly treated TB
- homeless, IV drug users
- patients in high risk congregate settings; prison, shelters, nursing homes, etc.
What 4 characteristics should make you always consider TB?
- resistance to simple antibiotics
- febrile (fever-like) illness
- chest infection
- unexplained cough
How does hemoptysis occur?
Through hemorrhage resulting from the extension of the caseous process into vessels of the cavity walls
How does tuberculous pneumonia occur?
marked inflammatory exudate filling the alveoli causes consolidation
How can a pleural effusion result from TB?
Seeding of the TB bacilli in the pleura, or hypersensitivity
Name 6 symptoms of TB?
- cough
- tiredness and malaise
- weight loss and anorexia
- fever (low grade)
- hemoptysis
- breathless if pleural effusion
Name 5 signs of TB
- palpable lymph nodes in 10%
- weight loss
- finger clubbing in long-standing disease
- fever
- pallor
How could you get miliary TB? Name 3 spots you could get more localized reactivation
If the rupture of caseous pulmonary focus gets into a blood vessel More localized reactivation: 1. pleura 2. lymph nodes 3. parts of the skeleton
Name some characteristics of pleural TB
More common in males, can cause tuberculous empyema
Name some characteristics of lymph node TB, which lymph nodes tend to be affected?
More common in women, children and asians. Often painless and most commonly cervical lymph nodes; can be discrete swelling to marked skin inflammation and rupture
What is the most common consequence of osteo-articular TB? What is it, and name 3 other possible osteo-articular TB consequences.
Most common is tuberculous spondylitis; starts in sub-chondral bone, follows longitudinal ligaments, mainly lower thoracic and upper lumbar spine and may progress to paralysis
Other: peripheral arthritis, osteomylitis, dactylitis, tendosynovitis
What does tuberculous spondylitis resemble?
Kyphosis
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Intro to Resp24
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Lung Ventilation17
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Lung Mechanics17
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Resp anatomy26
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Oxygen and CO2 in the blood17
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Chemical control of breathing + Long term changes18
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Lung Function Testing and Lung Imaging37
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Asthma35
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Lower Resp tract infections and pneumonia35
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TB41
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Lung Cancer30
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Interstitial Lung Disease35
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COPD29
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First Aid Embryology + Anatomy31
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First Aid Physiology60
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First Aid Pathology Pt 135
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First Aid: Obstructive and restrictive lung disease49
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First Aid: Pathology Pt 250
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First Aid Pathology Pt 3: Lung cancer and abscess33
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First Aid: Pharmacology37
