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S3 Respiratory > Tuberculosis > Flashcards

Tuberculosis Flashcards

1
Q

Risk factors for TB

A
  • non-UK born/ recent migrants (South Asia 54.8%, Sub-Saharan Africa 29.5%)
  • HIV
  • immunocompromised
  • homeless
  • drug users, prison
  • close contacts
  • young adults
  • elderly
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2
Q

Describe the microbiology of TB

A

Tuberculosis is caused by bacteria belonging to the Mycobacterium tuberculosis complex

7 closely related species
Mycobacterium tuberculosis
Mycobacterium bovis
Mycobacterium Africanum

Non-motile rod-shaped

Obligate aerobe

Long-chain fatty mycolic acids, complex waxes & glycolipids in cell wall

Structural rigidity, staining characteristics (acid alcohol fast needed)

Relatively slow-growing, generation time 15-20hrs

Latency period

Culture takes 6/12 weeks

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3
Q

Describe the transmission of Tb

A

Respiratory droplets, droplet nuclei suspended in air for a long time reach lower airway

Infectious dose 1-10 bacilli but prolonged exposure required (8hrs - 6months) e.g. households/ prisons/ schools

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4
Q

Describe the pathogenesis of Tb

A

Inhaled aerosols -> engulfed by alveolar macrophages -> local LNs -> primary complex/ infection (Ghon’s focus + draining LN) ->

Either:
Immune system failed - Progression to active disease (5%) primary

OR
Initial containment -> latent infection
-> (heals/ self cure (95%) Or reactivation and post primary TB)

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5
Q

What are the two forms of Tb infection? Explain the differences between them

A

Clinical infection (TB) - active, multiple tubercle bacilli, TST Or blood test usually positive, CXR usually abnormal, sputum smears/ cultures may positive, cough/ fever/ weight loss, often infectious b4 treatment = a case of TB (in the lungs)

Subclinical infection (LTBI) - latent/ inactive, contained tubercle bacilli, TST/ IFN game test usually positive, CXR usually normal, sputum smears/ cultures negative, asymptomatic, uninfectious = not a case of TB

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6
Q

What is primary TB?

A

Ghon focus/ complex (primary lesion usually subpleural)

Limited by CMI

Usually asymptomatic

Rare allergic reactions include erythema nodosum

Occasionally symptomatic & can disseminate e.g. miliary & extra pulmonary

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7
Q

What is post-primary TB?

A

Reactivation Or exogenous re-infection

> 5yrs after primary infection

5-10% risk per lifetime

Pulmonary or extra-pulmonary clinical presentation

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8
Q

Risk factors for reactivation of TB

A

HIV (all TB cases must be tested)

Substance abuse

Prolonged corticosteroids/ immunosuppressive therapy

Tumour necrosis factor- alpha [TNF-a] antagonists

Organ transplant

Haematological malignancy

Severe kidney disease/ haemodialysis

Diabetes mellitus

Silicosis

Low body weight

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9
Q

Sites of Tb disease

A

Pulmonary TB - lungs (most cases)

Extrapulmonary - larynx, LNs, pleura, Brain, kidneys, bones, joints, anywhere (found more in HIV/ immunosupressed/ young children)

Miliary TB - carried to all parts of body through bloodstream (rare)

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10
Q

Pathology of TB

A

Caseating granulomata (central necrosis)

  • lung parenchyma
  • mediastinal LNs

Giant cells (Langhans type granuloma) with epithelioid histiocytes (modified immobile macrophages) and lymphocytes

Slide 22

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11
Q

Symptoms and signs of pulmonary TB

A

Symptoms: fever, night sweats, weight loss & anorexia, tiredness & malaise, cough (most common), haemoptysis occasionally, breathlessness if pleural effusion

Signs: often no chest signs despite CXR abnormality, maybe crackles, extensive: signs of cavitation/ fibrosis, if pleural involvement typical signs of effusion

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12
Q

Investigations of pulmonary TB

A

CXR

Sputum - 3 early morning samples min volume 5ml

Induced sputum (inhales nebulised hypertonic saline solution)

Bronchoscopy (patients with dry cough)

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13
Q

Signs on a CXR for pulmonary TB

A

Apex of the lung often involved,

ill defined patchy consolidation,

Cavitation usually develops within consolidation,

Healing results in fibrosis

Pleural TB - pleural effusion

Slide 27

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14
Q

What are the benefits and negatives of TB microscopy?

A

Mainstay for TB diagnostics worldwide

auramine stained - Rapid (same day), cheap, high sensitivity, 60-70% culture positive samples are microscopy positive, ZN stained - indicates infectiousness as smear positive cases are more infectious than smear negative

But can’t differentiate between MTB and NTM (nontuberculosis myobacteria) or dead and live organisms

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15
Q

What are the benefits of TB culture?

A

Remains the gold standard for TB diagnostics

One of the most sensitive methods for mycobacteria

Solid and liquid culture systems

Improved with automated culture technology

Allows identification and susceptibility testing

E.g. Lowenstein Jensen slopes

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16
Q

What is the role of NAAT for primary samples?

A

Nuclei acid amplification tests

Rapid diagnosis of smear +ve

Shows Drug resistance mutations

Whole genome sequencing

17
Q

What is the Tuberculin sensitivity test? Negatives and benefits

A

Oldest diagnostic test - measures CMI (cell mediated immunity), in the form of DTH (delayed type hypersensitivity) to PPD (purified protein derivative) of M tuberculosis

Tuberculin injected intradermally - induration read 48-72hrs later

Subjective interpretation 
False positives (BCG, non TB)
False negatives (immunocompromised)

But cheap and evidence to support ability to predict active disease in those latently infected

18
Q

What are interferon Gamma Assays? (IFNg assay) when would you do this rather than skin testing? Drawbacks

A

modern alternative to skin testing

In-vitro test - Quantiferon Gold

T cell based assay (T spot) (causes bacilli to make interferon)

Measures antigen specific interferon gamma (IFNg assay)

✅no cross- reaction with BCG so do if known vaccination

Can’t distinguish between latent and active TB
Similar problems with sensitivity and specificity

19
Q

First line treatment of TB

A 
First line: RIPE
Rifampicin
Isoniazid 
Pyrazinamide
Ethambutol

RIPE for 2months and then just RI for 4
(18months if CNS TB) - cure rate 90%

  • adherence can do directly observed therapy or video observed

Vitamin D

Surgery

20
Q

Side effects of TB medications

A

RIPE ONGO

Rifampicin - orange secretions/ urine (raised transaminases & induces cytochrome P450)

Isoniazid - Neuropathy peripheral (10mg OD) + hepatotoxicity

Pyrazinamide - Gout + hepatotoxicity

Ethambutol - optic neuritis (visual disturbances)

21
Q

What are multi-drug resistant and extremely drug resistant TB?

A

Multi resistant (MDR): resistant to rifampicin and isoniazid

Extremely (XDR): resistant to R, I and fluroquinolones and at least one injectable

22
Q

Risks of developing drug resistant TB? How are they treated?

A

Inadequate treatment

Previous TB treatment

HIV

Known contact of MDR TB

Failure to respond to conventional treatment

> 4months smear +ve/ >5 months culture +ve

Given 4-5 drug regimen, longer duration - quinolones, aminoglycosides, PAS, cycloserine, ethionamide

23
Q

What is miliary TB?

A

Bacilli spreading through the blood stream - widespread infection

Either during primary infection or during reactivation

Lungs are always involved but few respiratory symptoms (fever, v unwell, dry cough)

Often multiple organs involved e.g. headaches- meningeal, pericardial/ pleural effusions small, ascites May, retinal involvement (choroid tubercles seen)

White specks on CXR slide 44

24
Q

Give examples of extra-pulmonary TB?

A

Lymphadenitis
Scrofula (glandular swellings)
Cervical most commonly
Abscesses and sinuses

Gastrointestinal
Swallowing of tubercles

Peritoneal ascitic Or adhesive

Genitourinary - slow progression to renal disease, subsequent spreading to LUT

Bone and joint - haematogenous spread, spinal TB most common, Pott’s disease

Tuberculosis meningitis - chronic headache, fevers, CSF markedly raised proteins, lymphocytosis

25
Q

Prevention of Tb

A

Notifiable disease - dr making/ suspecting diagnosis legally responsible for notification
-> triggers contact tracing procedures and provides surveillance data to detect outbreaks and mo it or epidemiological trends

Prevention of transmission - personal protective equipment, negative pressure isolation

Reduces susceptible contacts (risk factors reduced and vaccinations)

26
Q

What is the BCG and how effective is it?

A

Bacilli Calmette-Guerin live attenuated M.bovis strain

Babies high prevalence communities or children thought to have increased risk of coming into contact with TB/ new entrants from high risk areas/ health workers/ close contacts of active respiratory TB/ other groups

70-80% effective in revenging severe childhood TB

Little evidence in adults and protection wanes

Can’t be given to those with HIV as live vaccine

S3 Respiratory (21 decks)

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