Tuberculosis Flashcards
Tuberculosis
Tuberculosis (TB)= an infectious disease caused byMycobacterium tuberculosis, which typically affects the lungs due to the O2 supply.
Tuberculosis: Aetiology (Mycobacterium tuberculosis)
Mycobacterium tuberculosis is an aerobic, acid-fast bacilli.
- aerobic + slow dividing -> hard to culture
- acid-fast -> resistant to acid stain and gram stain due to waxy coat. Use Zeihl-Neelsen stain to stain red against blue background
- bacilli -> small, rod-shaped
Tuberculosis: Disease Course
inhalation of airborne droplet -> immediate clearance or primary infection (usually asymptomatic -> latency (non-contagious) -> secondary infection (when immunocompromised) -> miliary tuberculosis (disseminated and severe disease when the body cannot control the infection)
Tuberculosis: Risk Factors
Associated with exposure to TB:
- Close contact with active tuberculosis (e.g., a household member, relatives/immigrants from countries with high TB rates)
- Malnutrition, poverty, homelessness, prisons, hospitals
- smoking, alcohol, (IV) drug users
- previous or current respiratory co-morbidities
- non-respiratory co-morbidities (eg. diabetes, CVD, end-stage renal disease)
- Immunosuppression (eg. HIV, Immunosuppressant drugs or TNFα inhibitors)
Tuberculosis: Symptoms
Systemic symptoms:
* Fever, fatigue, myalgia, malaise
* Anorexia, weight loss
* night sweats
* lymphadenopathy
Pulmonary TB:
* Dysponea
* Chronic cough +/- haemopytsis
* Pleuritic chest pain
Extrapulmonary TB:
* Symptoms based on the organ-involvement (pleuritic chest pain, enlarged lymph nodes, spinal pain, headache, abdominal swelling and pain, urinary symptoms, skeletal pain, Erythema nodosum - tender, red nodules on the shins caused by inflammation of the subcutaneous fat, cold abscess - firm, painless abscess caused by tuberculosis, usually in the neck. ).
Tuberculosis: Disease Course cont.
Pulmonary TB refers to infection in the lungs, due to the O2 supply. Extrapulmonary tuberculosis refers to infection in other areas:
- Pleura
- Lymph nodes
- Pericardium
- Central nervous system
- Gastrointestinal system
- Genitourinary system
- Bones and joints
- Skin (cutaneous tuberculosis)
Tuberculosis: Examination Signs
Chest examination: crackles, bronchial breath sounds, or maybe normal.
Tuberculosis: Investigations
To determine cell-immunity to TB bacteria (previous, latent or active TB) but no active signs:
- Tuberculin Skin Test (TST), aka. Mantoux Test
- Interfon Gamma Release Assay (IGRA)
Pulmonary TB investigations for active signs:
- Chest Xray
- Primary: hilarlymphadenopathy effusion, pulmonary infiltrates, calcification.
- Reactivation: upper lobe cavitary lesion.
- Primary tuberculosismay show patchy consolidation, pleural effusions and hilar lymphadenopathy.
- Reactivated tuberculosis may showpatchy ornodular consolidation with cavitation (gas-filled spaces), typically in the upper zones.
- Disseminatedmiliary tuberculosis gives an appearance ofmillet seedsuniformly distributed across the lung fields.
- 4 sputum samples for microscopy, culture (gold standard), smear and NAAT
- microscopy: unreliable as Zeihl-Neelsen stain is only 55% specific
- culture (gold standard): difficult to culture so can take up to 6 weeks
- smear: stained red against blue background using Ziehl-Neelseen stain. the sensitivity is between 50-80%
this is decreased in individuals with HIV to around 20-30%
- NAAT: identify DNA of pathogen and compare it to that of TB. Also can identify gene sequences that code for drug resistance in multidrug resistant TB (MDR-TB)
If unable to get sufficient sputum - sputum induction by hypertonic saline - samples from bronchoalveolar lavage, pleural fluid, gastric aspiration, lung or pleural biopsy - blood culture
Extrapulmonary TB investigations for active signs:
- bodily secretions, tissue biopsy, lymph node biopsy depending on which organ is affected
Tuberculosis: Treatment
Latent tuberculosisis treated with either:
- Isoniazidandrifampicinfor 3 months
- Isoniazidfor 6 months (if HIV+ or have had organ transplant)
The treatment for active tuberculosis can be remembered with theRIPE mnemonic:
- R–Rifampicin for 6 months
- I–Isoniazid for 6 months + pyridoxine (VitB6) to prevent peripheral neuropathy
- P–Pyrazinamide for 2 months
- E–Ethambutol for 2 months
Side Effects of Drugs
- Rifampicin – hepatotoxicity and red/orange urine and tears and reduces the effects of drugs metabolised by cytochrome P450 enzymes, such as thecombined contraceptive pill (“red-I’m-pissin’”).
- Isoniazid– hepatotoxicity and peripheral neuropathy (+VitB6). (“I’m-so-numb-azid”)
- Pyrazinamide– hepatotoxicity and hyperuricaemia (high uric acid levels), resulting ingout and kidney stones.
- Ethambutol – colour blindness andreduced visual acuity (“eye-thambutol”)
- Liver functions tests should be checked prior to starting anti-tuberculosis medications and monitored throughout treatment.
- Visual acuity and renal function should be checked prior to starting ethambutol
- U+Es to monitor electrolyte disturbances and any elevation in Creatinine as a result of treatment.
- FBC as a baseline, and to assess for platelet count which can be important in the context of hepatotoxicity.
MDR-TB/Extrapulmonary TB:
- drug susceptibility testing
- longer, individualised treatment regimen developed with a specialist
Tuberculosis: Management
- Isolated management in negative pressure rooms to prevent airborne spread
- Specialised MDT team responsible for care
- Alert UK Health Security Agency of TB case
- Testing for other infectious diseases (eg. HIV, HepB, HepC)
- Testing contacts
Tuberculosis: Complications
- pleural effusion
- empyema
- Pneumothorax
- Bronchiectasis
- Pulmonary destruction
- Fistula
- Tracheobronchial stenosis
- Malignancy
- Chronic pulmonary aspergillosis.
- septic shock
- miliary TB
Tuberculosis: Screening
Screening for latent TB infection is done for:
- Individuals with recent exposure (contacts).
- Health care workers.
- Homeless shelters and prisons.
- Individuals with increased risk of reactivation: HIV.
- Travellers from high-incidence countries.
- Prevention:
- Bacille Calmette-Guérin (BCG) vaccination: children in high-risk region, health-care workers, and other individuals based on exposure status; should not be administered to individuals with decreased immunity.
- Isolate patient (short-term, until two weeks after initiating treatment), avoid new encounters, identify and treat the contacts.
- Reportable condition to the local health authorities.
