Tuberculosis Flashcards
What is TB
A caseating granulomatous disease caused by Mycobacterium tuberculosis - an intracellular organism that survives phagocytosis of macrophages
What are the 3 types of TB?
- Primary - infection is pulmonary and initial lesion heals as fibrosis. Can then become latent + become secondary later.
- Miliary - results from haematogenous dissemination of TB esp in immunocompromised patients.
- Secondary - caused by reinfection or reactivation in immunocompromised patients. Reactivation occurs in apex of lungs usually and can spread locally/to distant sites. Immunocompromise can come from immunosuppressant agents, HIV or malnutrition.
What are extra-pulmonary manifestations of TB?
- CNS - tuberculous meningitis
- Vertebral bodies - Pott’s disease
- Cervical lymph nodes - scrofuloderma
- Renal
- GI tract
What are the highest risk groups for TB?
Asian immigrants, immunocompromised/HIV patients
How does TB infection occur?
Results from the inhalation of aerosolised droplets containing the bacterium.
Deposits in the alveoli where it is engulfed by macrophages –> survives and multiplies in the macrophages –> proliferating bacteria kill macrophages resulting in immune response.
Leads to:
1. Clear infection
2. Latent infection
3. Primary disease - Tcells and macrophages form a granuloma with a necrotic core of caseous material preventing growth and spread of TB (non-infectious latent TB Th1 cells)
What does TB transmission depend on?
- Degree of exposure - proximity, ventilation, length of exposure
- Susceptibility of person - immunocompromised
What are TB risk factors?
- Endemic country birth
- Close contact
- HIV
- Immunosuppression
- IVDU
- Alcoholism
- Uncontrolled diabetes
What are extrapulmonary features of TB?
- Meningitis (neck stiffness, headache, photophobia)
- Choroiditis (blurred vision, red eyes)
- Constrictive pericarditis (chest pain, SOB)
- Dysuria, haematuria
- Abdo pain, mass in RIF, ascites, distended abdomen
- Potts disease + arthritis/osteomyelitis
- Lupus vulgaris: brown plaques that ulcerate, occuring at mucocutaneous junctions
- Constitutional symptoms
90% of cases are only pulmonary
What are constitutional symptoms?
Fever/Chills, Night sweats, Fatigue, Loss of Appetite, Weight loss, Lymphadenopathy
What are the initial steps when pulmonary TB suspected?
- Isolate
- CXR: Patchy nodal shadows in upper zones, cavitating lesions, apical lesions, miliary TB shows multiple 1-10mm nodules throughout lungs
- 3 sputum cultures for acid-fast bacilli smear + culture - NAAT on 1 resp sample and ZN stain (rapid direct microscopy for acid fast bacilli)
What are the 4 TB drugs and their function?
R - Rifampicin - inhibits DNA transcription (bactericidal)
I - Isoniazid - inhibits synthesis of cell wall (bactericidal)
P - Pyrazinamide - lowers intracellular pH, disrupting synthesis of fatty acids (bactericidal)
E - Ethambutol - interferes with cell wall synthesis (bacteriostatic)
What are the SEs of the TB drugs?
Rif - Anorexia, pseudomembranous colitis, hepatotoxicity, orange colouration of excreted fluids, drug interactions
Iso - Constipation, peripheral neuropathy, hepatitis, SLE symptoms, vomiting
Pyra - Sideroblastic anaemia, hepatotoxicity, arthralgia
Etham - optic neuritis –> red/green colourblindness, neuritis
Elaborate on the TB drugs and their resistance
Rif - also used in mycobacterial infection - widespread resistance develops rapidly
Iso - bactericidal on dividing and static on resting - rapid resistance if used alone
Pyra - only active against mycobacteria - rapid resistance if used alone
Etham - only active against mycobacteria - resistance uncommon
