TB Flashcards
Describe the pathogen responsible for TB
Mycobacterium tuberculosis
Non motile bacilli
Obligate aerobes
Can’t be detected by gram stain (lipid rich cell wall)
Slow growing (take at least 3 weeks to culture)
How is TB spread
Respiratory droplets via aerosol
Requires prolonged exposure so is commonly spread in families, prisons and homeless shelters
Risk factors for TB
HIV Silicosis IVDUs Prolonged corticosteroid therapy TNF alpha antagonists Diabetes Immunocompromised Asian Severe kidney disease Chronic lung disorder
What needs to be done immediately when TB is suspected
Contact TB radiology Referred to TB clinic Questionnaire Take sputum sample Start treatment within a week
What happens once M. Tuberculosis is inhaled
Engulfed by alveolar macrophages but resists phagocytosis
IL12 is released which stimulates IFN gamma and TNF alpha release - recruits macrophages which forms granulomas
Macrophages travel to local lymph nodes forming a Ghon complex
What is a Ghon complex
Ghon focus - nodular inflammatory lesion in the lung parenchyma with central caseous necrosis
Lymphadenitis of draining lymph nodes
Lymphangitis of lymph vessels connecting Ghon focus and draining lymph nodes
What happens to the Ghon complex
Progresses to active TB (primary TB)
Or
Is contained (no multiplication) so latent TB occurs
Latent TB either resolves or is reactivated/reinfected leading to post primary TB
Symptoms and signs of pulmonary TB
Symptoms: fever, night sweats, weight loss, malaise, cough, haemoptysis, dyspnoea if pleural effusion
Signs: cavitation within consolidation in CXR, crackles
Describe pleural TB
Can result from hypersensitive response to primary TB or from tuberculous empyema with a ruptured cavity
Can lead to pleural effusion causing breathlessness
More common in males
Describe lymph node TB (scrofula)
Often painless swelling of lymph nodes, usually cervical
More common in children, women and Asians
Describe osteoarticular TB
Potts disease (tuberculous spondylosis) - spread to vertebral bodies and ligaments, usually thoracic and lumbar Poncet's disease - aseptic arthrosis mainly affecting knees, elbows and ankles
Describe tuberculous meningitis
Altered consciousness
Headache
Fever
CSF appear cloudy (WBC and proteins)
Describe Miliary TB
TB spreads into the bloodstream
Symptoms: consolidation of both lungs, headaches if meningeal involvement, ascites, pericardial and pleural effusions
How is TB diagnosed
Clinical features
Shadowing, cavitation, consolidation, cardiomegaly and miliary seeds on CXR
Culture of appropriate body fluid (3 sputum) and ZN or auramine stains
Histology - TB granulomas (central caseous necrosis, Langhan’s giant cells)
How do you diagnose latent TB
Tuberculin skin test - inject tuberculin intradermally and measure induration 2-3 days later (false positive with BCG and false negatives in immunosuppressed)
Interferon gamma releasing assay - no cross reaction with BCG
