Lung Infections: Tuberculosis Flashcards
Definition
NOTIFIABLE DISEASE: Infectious granulomatous disease caused by mycobacterium tuberculosis
- in most patients remains dormant before progresses to active TB
- multidrug resistant TB = strain of TB that is resistant to 2 first line drugs (isoniazid + rifampicin)
Why is tuberculosis resistant to killing by lysosome + its enzymes
Due to its waxy mycolic acid capsule
Which stain is used to identify M. tuberculosis
Ziehl Neelson Stain
Epidemiology
Africa + Asia
Prevalent in immunocompromised (e.g. HIV)
Risk factors
Contact with a person with active TB
Endemic regions
Homelessness
Alcohol or drug abuse
Immunocompromised
Silicosis
Aetiology
Mycobacterium Tuberculosis
Pathophysiology
Alveolar macrophages struggle to clear the mycobacteria due to its waxy myoclonic acid capsule which confers protection and prevents binding normal stains
It spreads via respiratory droplets
They are very slow dividing with high O2 demands
What is primary TB
First infection with the mycobacteria
Alveolar macrophages ingest TB but cannot release lysosomes to kill it
TB survives + multiplies inside it then kills macrophages + is released
Immune cells surround TB = forming granuloma (Ghon focus) to wall off the bacteria.
The tissue inside dies = caseous necrosis
Can spread to hilar lymph nodes = Ghon complex = undergoes fibrosis into Ranke complex
What is latent TB
Infection without disease due to it being walled off by the granuloma
Patient is asymptomatic + non-infectious but blood test to show infection
What is secondary TB
If the person is immunocompromised (HIV, AIDS, ageing) the latent TB can become re-activated
Lung apex (top of lung) as PO2 is highest
Patient are infectious
Show haemoptysis + fever
What is milliary TB
This is where bacteria spread systematically following secondary TB
Can spread to:
- Kidneys = pyuria (WBCs in urine)
- Meninges = meningitis
- Lumbar vertebrae = Potts Disease
- Adrenal glands = Addison’s Disease
- Liver = Hepatitis
- Cervical lymph nodes = lymphadenitis in neck
- GU = tuberculosis epididymitis
Signs
Auscultation: often normal; crackles may be present
Clubbing; if long standing
Spinal pain/ Potts disease
Erythema Nodosum = red painful tender lumps
Symptoms
Chest pain
Lethargy
Cough with or without haemoptysis
Dyspnoea
Systemic symptoms:
- Fever
- Weight loss
- Night sweats
- Lymphadenopathy
Extrapulmonary Symptoms
Tuberculosis Meningitis =
- Fever
- Neck stiffness
- Photophobia with a headache
Potts Disease (vertebrae) =
- Lower back pain,
- Leading to vertebral narrowing and spinal damage
Urogenital TB =
- cystitis unresponsive to antibiotics
- dysuria
- frequency
- haematuria
Miliary TB =
- This is when TB becomes disseminated leading to formation of granulomas throughout body
Latent Disease Investigations
LATENT DISEASE = Mantoux screening: for latent infection in asymptomatic patients at high risk.
- Induration of 5mm or more = POSITIVE TEST
- Possible previous vax or previous infection
- Does not differentiate between active or latent disease
INTERFERON GAMMA RELEASE ASSAY =
- confirm latent TB in those who have +ve mantoux test
