Tuberculosis Flashcards
What is the epidemiology of TB ?
The disease burden is falling incidence rate is falling about 2% a year
TB deaths have fallen by 29% since 2000
Number 1 killer of communicable diseases
TB kills more than HIV and malaria together
2 billion infected worldwide
How many of the 2 billion infected people with tuberculosis have HIV ?
1.1 million
What groups are vulnerable to TB ?
Those from high prevalence countries
70% are non-UK born, most ages between 15 and 44
HIV positive, immunocompromised
Elderly, neonates, diabetics
Homeless, alcohol dependency, IVDUs, those with mental health problems and those in prisons- approx. 1/10 of all cases
What is the microorganism responsible for TB ?
Mycobacteria
What are the specific names for the organisms responsible for TB ?
Mycobacterium tuberculosis
M. bovis (“bovine TB”)
M. Africanum
Are all AAFB TB ?
No
Describe the type of bacterium that Mycobacterium TB is ?
Non-motile bacillus
Very slowly growing
Aerobic - predilection for apices of lungs (ventilated but not perfused)
Very thick cell wall lipids, peptidoglycans, arabinomannans
Resistant to acids, alkalis and detergents
Resistant to neutrophil and macrophage destruction
Aniline based dyes such as carbon fuchsin complex with cell wall
Unable to remove dye from cell wall
Acid - and alcohol - fast bacilli (AAFB) (Ziehl Neilson stain)
How is TB transmitted ?
Airborne
Coughs, sneezes, yells, sings
Aerosol droplets which can remain suspended in air for many hours
Prolonged close contact
How can M. Bovis be transmitted ?
Consumption of unpasteurised cows milk (UK)
What removes mycobacteria outdoors ?
UV radiation
Dilution
Who is normally affected by the primary infection ?
Usually children, 80% Infected focus in alveolus, (lymph nodes, gut)
Where do mycobacteria spread to once they are in the alveoli ?
Spread via lymphatics to draining hilar lymph nodes
Then there is haematogenous seeding of mycobacteria to all organs of the body (lung, bone, genitourinary system)
What are the symptoms of TB ?
Usually no symptoms, can be fever, malaise, erythema nodosum, rarely chest signs
What are the three outcomes of a primary infection ?
Progressive disease - ineffective immune response from the patient
Contained latent - activates when the patient becomes immunosuppressed (old)
Cleared and cured
How common is a primary infection of TB ?
Small percentage (1%)
How does a primary infection of TB progress ?
Primary focus continues to enlarge - cavitation
Hilar lymph nodes become enlarged to the point they compress bronchi causing lobar collapse
Lymph node discharges into bronchus (tuberculosis bronchopneumonia)
Describe the incidence and findings in miliary TB ?
Small percentage (1%)
6-12 months after infection
Fine mottling on the X-ray, widespread small granulomata - looks like millet seed in the lung - very serious
How can TB affect the CSF and the pleura ?
Can cause meningeal TB (severe, CSF high protein, lymphocytes)
AND
Tuberculosis pleural effusion
What is meant by post primary disease ?
Reactivation of mycobacterium from latent primary infection disseminated by the blood stream around the body
New re-infection from outside source
What are the sites of post primary disease from TB ?
Pulmonary disease
Lymph nodes, usually cervical
Bone and joint; spine, hip, etc
Genito-urinary; kidney, ureter, bladder
Males; infertility - vas deferens
Females; infertility - uterus, Fallopian tubes
Pericardium; constrictive pericarditis
Abdomen; ascites, ileal TB obstruction
Adrenal Addison’s disease
Skin; lupus vulgaris
Just about any other tissue!
What are the features of TB usually after 6-12 months ?
Miliary , meningeal, pleural TB
What are the features of TB after 1-5 years ?
Post primary disease - pulmonary and skeletal
What are the features of TB after 10 years ?
Genitourinary, Cutaneous TB
How would you describe the progression of Post-primary TB ?
Slow, may be no symptoms for many months
What are the symptoms for Post primary TB ?
Respiratory; cough, sputum, haemoptysis, pleuritic pain or breathlessness
Systemically unwell
Malaise, fever, weight loss (“night sweats”) - very characteristic of TB
What is characteristic PMH for Post-primary Pulmonary Tuberculosis ?
Diabetes, Immunosuppressive diseases, Previous TB
How is post-primary TB diagnosed ?
Classical: apices, soft ‘fluffy’/nodular upper zone, cavitation in 10-30%
Lymphadenopathy rare
Normal CXR in 13% of definitive plum, TB (22% in HIV)
When should a CT be considered ?
Normal CXR but clinical suspicion
Miliary TB
Caviation and other differentials
Lymphadenopathy, alternative diagnosis
Targets for BALWhat are the means of diagnosing TB ?
Sputum analysis
Chest radiograph
CT scan of thorax
Bronchoscopy with alveolar lavage, transbronchial biopsy
Pleural aspiration and biopsy if pleural effusion
How do we analyse sputum samples for TB ?
ZN stain - immediate answer if AAFB
Culture
Sputum PCR
What features of a chest radiograph confirms presence of TB ?
Patch shadowing, often in apices/upper zones, or apex or lower lobes
Cavitation
Calcification if chronic or healed TB
What happens after the fluid is collected from the pleural aspiration ?
Fluid cytology (lymphocytes)
Fluid for AAFB and culture
Biopsy histology
1 biopsy sent in Saline for culture
What is treatment of tuberculosis ?
Vitamin D causes macrophages to release Cathelecidin which is a very potent antibiotic.
Surgery - Collapse of the cavity by: Phrenic crush (crushing the phrenic nerve causes the diaphragm on that side to become paralysed and rise up, closing the cavity), artificial pneumothorax (collapses the lung and therefore the cavity), pneumoperitoneum, thoracoplasty (Six to eight ribs were broken and pushed into the thoracic cavity to collapse the lung beneath), lung resection (removal of a segment of lung).
How are drugs used against TB ?
Multiple used to prevent resistant organisms forming,
Therapy at least 6 months, slowly growing organism
ONLY SPECIALISTS TREAT
What are the legal requirements behind treating TB ?
Legal requirement to notify all cases
low threshold for HIV testing, AIDS defining condition
What are the drugs used for TB management ?
Streptomycin Isoniazid Pyrazinamide Rifampicin Ethambutol
What are the side effects of Rifampicin ?
Orange urine, tears, induces liver enzymes, prednisolone, anticonvulsants, oral contraceptive pill is ineffective
Hepatitis
What are the side effects of Isoniazid ?
Hepatitis Peripheral neuropathy (pyridoxine B6)
What are the side effects of Pyrazinamide ?
Hepatitis
Gout
What are the side effects of Ethambutol ?
Optic neuropathy
What can all 4 drugs also cause ?
Rash
What is the point of TB contact tracing ?
Find out where the patient has caught it and who they might have spread it to
Likelihood of infection with TB depends on ?
Duration of contact
Intensity of infection
What is the treatment for latent TB ?
Rifampicin & Isoniazid for three months, or
Isoniazid only for six months, or
Rifampicin only for six months, or
Rifapentine & Isoniazid once weekly for 12 weeks (underserved population)
