Tuberculosis Flashcards
What can happen to the spine in children suffering from TB?
Complain of back pain - spine can stick out due to collapse of some of the vertebrae
- crumbling vertebrae occurs over weeks - help to prevent rapid paralysis
What stain is used for TB?
Ziehl-Neelson stain - mycobacteria doesn’t have a peptidoglycan cell wall therefore gram staining doesn’t work
What are the organisms that cause TB?
Mycobacterium Tuberculosis
- group of organisms, M. TB complex cause TB: M. tb, M bovis, M africanum, M microti, M canetti
How is TB transmitted?
inhalation of infectious droplets - cough, sneeze, shout, sing
- it cannot be passed from the brain to someone else
What factors influence the probability of TB being transmitted?
Infectiousness of case (number expelled into the air)
Environmental factors affecting concentration (air flow)
Proximity, frequency, duration of exposure (work, home)
Susceptibility of exposed person
What is the difference between latent and active TB?
About 1/3 world pop has latent TB but they don’t suffer symptoms and can’t pass it on
10% can’t control their TB so it becomes active
If it enters the blood it can spread anywhere
What is the pathophysiology of latent TB?
Macrophages ingest tubercles to form granulomas
2-8 weeks after latent TB infection it can be detected by TST or interferon-gamma release assay
Immune system able to stop multiplication and control infection
Pts not infectious and asymptomatic
Risk of reactivating
- 10% over lifetime
- 10% per year if untreated HIV
- risk is higher in children under 5 and immunosuppressed
What is the pathophysiology of active TB?
Granulomas breakdown and bacilli escape/multiply
May occur at time of original infection or years later
Open/Pulmonary TB is infectious
Extrapulmonary TB is usually not infectious
Symptoms:
- cough (if pulmonary)
- fever
- night sweats
- weight loss
- local symptoms (back pain, joint pain, Lnopathy, meningitis)
How does miliary TB present?
Very variable
Acute disease can be fulminant- sepsis, multiorgan failure, ARDS
Subacute/chronic (median duration= 2 months)
- general = failure to thrive, sweats, pyrexia
- Pulmonary = cough, SOB, pain, hypoxia
- Lymphatic= enlargement, airway compression
- bone/joint= pain, neurology
-GI = pain, pancreatitis, peritonitis, hepatitis
- CNS = meningitis, tuberculoma
- GU = haematuria, sterile pyuria, cystitis, hydronephrosis, scrotal pain, menstrual abnormalities
- adrenal = <40% of cases but overt addison’s
- CV = pericarditis
- Skin = cutis miliaris disseminata
How do you diagnose latent TB?
Tuberculin skin test - mantoux
Interferon gamma release assay
How do you diagnose active TB?
Clinical awareness
Radiological appearances
Microbiological samples - grow TB (sputa, CSF, vbiospy), PCR
Histology - caseating granulomas, AFBs (acid fast bacillus)
What do the results of a mantoux test show?
<6mm = negative >6mm = positive if not BCG >/= 15mm positive if BCG
How does the IGRA test work?
Helps to diagnose latent TB
Benefit of not cross-reacting with BCG and largely unaffected by previous infection with NTM
Surrogate marker for MTB indicating a cellular response to MTB - cannot distinguish between latent and active
>95% sensitive for diagnosis of latent TB
Poor for diagnosis of active TB
Sensitivity diminished by low CD4 count
What are the UK recommendations for diagnosis?
Mantoux 1st line for latent TB diagnosis
IGRA in those with BCG borderline results
IGRA + mantoux in those with HIV and low CD4
IGRA with or without mantoux in immunocompromised
IGRA useful in hard to reach groups
What are the problems with IGRA?
Variable results with serial testing - utility influenced by prevalence and BCG use
Questions of reproducibility especially if results are borderline
Expensive and need fresh blood to be rapidly processed (T-spot 8 hours of collection, quantiferon 16 hours after collection)
Interderminate results- esp. in HIV or pts on anti-TNF treatment
