Tuberculosis Flashcards
What is the bacteria causing TB? How would someone become infected and what parts of the body can be affected?
Mycobacterium tuberculosis
Contagion occurs through airborne particles
Brain/bloodstream/lungs/peritoneum/LN
What form of inflammation does TB cause? What role do macrophages have in this response?
Granuloma=Aggregation of macrophages which can fuse to form a giant cell and are surrounded by lymphocytes and which has a central necrosis area (caseous)
Macrophages engulf and encase TB to prevent dissemination of TB
TB can present as a primary disease or as latent infection. What is the difference? Who do they commonly affect?
Primary= organism continues to divide due to weakened granuloma due to weakened immune system i.e. seen in children and HIV patients
Symptoms w/i 1 year
Latent= functioning granuloma prevents organism from dividing so TB is dormant
Can lead to secondary TB or nothing depending on whether granuloma remains intact
What is secondary TB?
Latent reactivation of dormant TB due to decline in health or immunity causing granulomas to weaken which enables TB dissemination
PRESENTS YEARS POST EXPOSURE
What are the 2 tests which can be done to test for latent TB and what do they involve?
Tuberculin Skin Test (TST)= indicates person been exposed to TB at some point in life
-tuberculin injected under skin to cause a type 4 sensitivity reaction and raised lump measured to
POSITIVE= >5mm
Interferon Gamma Release Assay (IGRA) i.e. Quantiferon or T-Spot
-measure amount of interferon released in response to TB
What can IGRA and TST not indicate? What is the follow up for these tests?
Cannot say if person has active TB- need to follow up symptoms to see if indicates active TB
Positive= follow up to assess for active TB
Negative= BCG if in high risk area
What are the common symptoms associated with TB?
CONSUMPTION SIGNS:
- Fever
- Weight loss and fatigue due to long term inflammatory state
- Night sweats due to TNF alpha
SIGNS OF LOCALISED INFECTION:
- cough/haemoptysis
- Abdominal
- headache
- back pain
Which part of the lungs are affected by TB and what are the associated x-ray changes?
Upper lobes
Changes:
- upper lobe opacification= RUL consolidation
- ring-like lesions (NOTE: more likely to indicate cancer in older patients)
- Cavitatory lesions
- millet seed pattern for miliary TB
What are the possible differentials for fever/weight loss/night sweats?
Cancer Infection: -acute= bacterial -chronic or weakened immune= fungal Inflammatory conditions
What are other causes of granuloma formation?
Sarcoidosis Crohn’s disease Granulomatosis with polyangiitis (GPA) Syphilis Pneumotitis in PCP (pneumocystis pneumonia) + HIV Systosomitis Foreign body
Why are TB drugs used in combination? What are these drug combinations?
High risk of resistance to drugs
2 months RIPE
- Rifampicin
- Isoniazid
- Pyrizinamide
- Ethambutol
4 months RI
What are the side effect of TB drugs?
Rifampicin= Orange urine and tears Isoniazid= peripheral neuropathy Pyrazinamide= hepatic toxicity and hepatitis Ethambutol= optic neuritis + visual problems
What is process is required for a TB diagnosis? What samples are taken? NOTE: think about the different types of TB.
Microbiology to detect mycobacterium tuberculosis
- 3 x early morning sputum on consecutive days
If unable to attain sputum (children swallowing or low production):
-broncho-alveolar lavage
-gastric lavage - Blood = is milliary TB suspected
- CSF= TB meningitis
- Tissue= organ TB
What are the 4 main bacteria species classified as mycobacterium?
Mycobacterium tuberculosis
Mycobacterium tuberculosis complex
Mycobacterium leprae
Non-tuberculous mycobacteria (NTM)= disease in weakened immune system
Mycobacterium TB is an “acid fast” bacilli. What does this mean? What are the consequences?
Doesn’t stain well with gram straining due to mycolic acid in cell walls meaning it has a high lipid content
Poor dye absorption but good retention
