Tuberculosis Flashcards
What happens in primary TB?
1st encounter
Host macrophages in the lung engulf the organisms + carry them to hilar lymph nodes in an attempt to control infection.
Small granulomas (tubercles) are formed around the body to contain the mycobacteria
What is the outcome of primary TB?
80% heal spontaneously + bacteria are eliminated
20%: bacteria encapsulated in a defensive barrier but persist in an otherwise healthy individual where disease is dormant
What is secondary TB? What is it usually precipitated by? Where does it usually occur?
Reactivation of semi-dormant TB
Precipitated by impaired immune function: malnutrition, AIDS or immunosuppressive therapy.
Occurs in lung apices
List 7 risk factors for TB
Close contact with TB patient
Ethnic minority groups (sub-saharan Africa + S. Asia)
Homeless, alcohol dependent, drug misusers
HIV+, immunosuppressed
Elderly
Co-morbidities
Children
How do primary and secondary tuberculosis patients present?
1: usually asymptomatic.
2: variable + nonspecific
List 8 general symptoms a patient with TB may complain of
Fatigue Malaise Fever Weight loss Anorexia Night sweats Clubbing Erythema nodosum
What pulmonary symptoms occur in TB?
Chronic, productive cough/ Haemoptysis
Purulent ± bloodstained sputum
What genitourinary, musculoskeletal, CNS, and GI symptoms may arise from caseous tubercles spreading in miliary TB?
GU: Sterile pyuria, Infertility
MSK: pain, arthritis, osteomyelitis, Pott’s disease, spinal cord comp. + abscess formation
CNS: meningitis + tuberculomas: headaches, vomiting
GI: Subacute obstruction, COBH, Weight loss, Peritonitis, Ascites
What is TB?
Granulomatous disease caused by Mycobacterium tuberculosis
What are the 3 subtypes of TB?
Primary: initial infection; pulmonary or GI (rare)
Post-primary: Reinfection/ reactvation
Miliary: Haematogenous dissemination
Give 4 features of Mycobacterium Tuberculosis
Intracellular organism
Acid fast bacilli
Survives after being phagocytosed by macrophages
Aerobe: prefers upper lung lobes
Describe the epidemiology of TB
Annual mortality = 1.5 million (95% in developing countries)
Annual UK incidence = 8000
Asian immigrants = highest risk group in UK
List 6 signs and symptoms in primary TB
Mostly ASYMPTOMATIC Fever Malaise Cough Wheeze Erythema nodosum Phlyctenular conjunctivitis
List 7 symptoms in post-primary TB
Fever/ night sweats Malaise Weight loss SOB Cough with purulent, blood streaked sputum Pleuritic chest pain Clubbing
List 6 signs and symptoms in miliary TB
Fever Weight loss Cough SOB Meningitis Yellow caseous tubercles spread to other organs
What investigations should be performed for TB?
Sputum/ Pleural Fluid MC+S CXR Raised WCC + Anaemia HIV Testing CT, lymph nodes, pleural biopsy, sampling of other affected systems
What is seen on CXR in primary TB?
Peripheral consolidation
Hilar lymphadenopathy
What is seen on CXR in post-primary TB?
Upper lobe shadowing Streaky fibrosis + cavitation Calcification Pleural effusion Hilar lymphadenopathy
What is seen on CXR in miliary TB?
Fine shadowing
Nodular
What group of antibiotics are used to treat TB?
Rifampicin (6months)
Isoniside (6months)
Pyrazinamide (2months)
Ethambutol (2months)
What is extra pulmonary TB? In which patients does this most commonly occur?
TB involving organs other than the lungs
Immunocomprimised
What lymph, dermatological, CVS and adrenal signs and symptoms may arise from caseous tubercles spreading in miliary TB?
Lymphadenopathy
Skin: lupus vulgaris
Heart: pericardial effusion, constrictive pericarditis
Adrenals: Addisons
How does primary TB present?
Mostly asymptomatic
May have vague flu like symptoms
What is the gold standard investigation for TB? What is the issue of relying on this?
Sputum culture + Ziehl-Nielsen staining
Culturing TB takes a long time (~ 6 weeks)
When are IGRAs useful? What occurs?
Useful in latent TB (high specificity)
Negative in BCG vaccine
Exposure of host T cells to TB antigens leads to release of interferon
Why is IGRA testing preferred to TSTs?
Single patient visit
BCG does NOT give false positive
What are the 2 forms of testing for TB?
Tuberculin Tests: Mantoux test +Heaf Test
Interferon Gamma Tests (IGRA)
How should cultures be taken in suspected TB?
Sputum acid-fast bacilli smear (3 samples 8 hours apart, with 1 being in early morning)
What is shown by tuberculin skin tests?
Positive if previous exposure to TB or BCG
Negative TST doesn’t rule out TB
What is the Mantoux test? What does it identify?
Erythema after 72hrs of PPD injection suggests patient has previously been exposed to TB.
Identifies those exposed to TB
DOES NOT distinguish between active + latent TB.
What is the Heaf test? How is it interpreted?
PPD on forearm. Graded according to papule size + vesiculation
(ring-shaped induration)
What is the limitation of the IGRA test?
Does not differentiate between latent + active TB
What is a Gohn focus?
Granuloma in which central tissue has died due to caseous necrosis
Sequela of primary TB infection
What is a Ghon complex comprised of? What may this progress to if calcified?
Ghon focus + ipsilateral mediastinal lymphadenopathy
Ranke complex
What is a Ranke complex?
a Ghon lesion that has undergone calcification
+
an ipsilateral calcified mediastinal node
Which anti-TB antibiotic causes optic neuritis? How may this present?
Ethambutol
Loss of colour vision + visual acuity
Which anti-TB antibiotic is an enzyme inducer? Thus what drugs need to be considered?
Rifampicin
OCP
Which anti-TB antibiotic causes peripheral neuropathy?
Isoniazid
Which anti-TB antibiotics are hepatotoxic?
Rifampicin
Isoniazid
Pyrazinamide
