tb Flashcards
definition of TB
Granulomatous disease caused by Mycobacterium tuberculosis.
primary - initial infection may be pulmonary (acquired by inhalation from the cough of an infected patient), or occasionally GI
miliary TB - results when there is haematogenous dissemination
post-primary - caused by reinfection/reactivation
aetiology of TB
recent travel
born in foreign country
family member exposed
M. tuberculosisis an intracellular organism (also known as acid-fast bacilli, AFB) which survives after being phagocytosed by macrophages.
pathophysiology fo active tb
when containment by immune system (T cells/macrophages) is inadequate
from primary infection or re-activation of previously latent disease
Transmission of TB is via inhalation of aerosol droplets containing bacterium.
This means only pulmonary disease is communicable.
pathophysiology of latent TB
infection without disease due to persistent immune system containment (ie granuloma formation prevents bacteria growth and spread).
+ve skin or blood testing shows infection, but no symptoms and pt non-infectious (normal sputum/CXR)
approx 2billion people expected to have latent TB
lifetime risk of reactivation 5-10%
RF for reactivation of TB
new infection (<2yr)
HIV
organ transplantation
high risk settings (homeless shelter, prison)
low socioeconomic status
haemodialysis
epi of TB
Annual mortality 3 million (95% in developing countries); annual UK incidence 6000.
Incidence in Asian immigrants>30 times native UK white population.
- 6 million new cases/yr of which 37% are unreported/undiagnosed
- 3% of new cases, and 20% of previously treated cases are drug resistant
Co-infection with HIV in 12% of new cases.
Leading cause of death worldwide, 1.5 million deaths/yr.
Effective diagnosis and treatment saved 43 million lives between 2000and2014.
UK ~8000/yr, ~12 per 100000. 73% born outside UK, 70% in deprived areas, 30% with pulmonary disease wait >4 months from symptoms to treatment.
sx of TB
haemoptysis
night sweats - B cell symptoms
fever
SOB
sx of primary TB
mostly asymptomatic
fever
malaise
cough
wheeze
erythema nodosum
phlyctenular conjunctivitis - allergic manifestations
miliary TB
Haematogenous dissemination leads to the formation of discrete foci (~2mm) of granulomatous tissue throughout the lung (‘millet’ seed appearance).
fever
weight loss
meningitis
yellow caseous tubercles spread to other organs (eg in bone and kidney - may remain dormant for years)
sputum may be -ve because spread is haematogenous = low threshold for LP
sx of post-primary tb
- fever/night sweats
- malaise
- weight loss
- breathlessness
- cough - dry then productive
- sputum
- haemoptysis
- pleuritic pain
- signs of pleural effusion
- collapse
- consolidation
- fibrosis
non-pul TB
in immunocompromised
TB LN
suppuration of cervical/supraclavicular nodes = abscesses or sinus = discharge pus and spread to the skin (scrofuloderma)
node firm to touch and not acutely inflammed - cold abscess
Skin can adhere to the underlying mass with risk of rupture and sinus formation
Investigate with fine-needle aspiration, AFB staining, and culture
CNS TB
Haematogenous spread leading to foci of infection in brain and spinal cord
foci can enlarge = tuberculomas.
Foci rupture = meningitis.
Increased risk with HIV, immune suppression and <3yrs
headache
meningism
confusion
seizures
focal neurological deficit
systemic symptoms
Needs LP and examination of CSF (leucocytosis, raised protein, CSF: plasma glucose <50%, AFB stain, PCR and culture). Look for TB elsewhere (CXR, etc), test for HIV. CT/MRI may show hydrocephalus, basal exudates. Tuberculomas are ring-enhancing.
skin TB
lupus vulgaris = persistent, progressive cutaneous TB: - jellylike reddish-brown glistening plaques
Scrofuloderma: skin lesion extended from underlying infection eg lymph node, bone; causes ulceration and scarring
heart TB
pericardial effusion
pericarditis/constrictive pericarditis
Myocardial involvement (arrhythmias, heart failure, ventricular aneurysm, or outflow obstruction) is rare.
Check chest imaging for other TB pathology, eg pulmonary disease, mediastinal lymph nodes.
GI TB
- subacute obstruction - due to bowel wall thickening, stricture formation or inflammatory adhesions
- change in bowel habit
- weight loss
- peritonitis
- ascites
- most disease is ileocaecal
- colicky abdominal pain
- biopsy needed for diagnosis
- Caseation necrosis and an absence of transmural cracks/fissures distinguish from Crohn’s disease.
GU TB
symptoms may be chronic, intermittent or silent
UTI symptoms
dysuria, frequency, loin pain, haematuria, sterile pyuria
renal failure
epididymitis
endometrial or tubal involvement
infertility
Granuloma may cause fibrosis, strictures, infertility, and genital ulceration.
endo TB
adrenal insufficiency
bone/joint TB
osteomyelitis
arthritis
paravertebral abscesses
vertebral collapse - Pott’s disease
spinal cord compression from abscesses
local pain and tenderness for weeks/mo
slow insidious progression
may not present until deformity or neurological symptoms
systemic TB feature
low grade fever
anorexia
weight loss
malaise
night sweats
clubbing (bronchoectasis)
erythema nodosum
An aspergilloma/mycetoma may form in the lung cavities.
Ix for latent TB
tubercilin tests - positive in previous exposure M. tuberculosis or BCG, strongly positive may indicate infection
mantoux test - Intradermal injection of purified protein derivitive (PPD) tubercilin, induration and erythema after 72 h. Size of skin induration is used to determine positivity depending on vaccination history and immune status (>5mm if risk factors, >15mm if no risk factors).
Heaf test - place drop of PPD on forearm, fire spring-loaded needled gun, read after3–7 days. Graded according to papule size and vesiculation.
INF-y test - in latent TB exposure of host T-cells to TB ag = release of INF. high specificity (negative with BCG vaccination) so can be used to diagnose latent TB if tubercilin is +ve
ix for latent TB
CXR
HIV test - Recommended to coincident disease (2% may be HIV positive).
Sputum/pleural fluid/bronchial washings: Microscopy (Ziehl–Neelsen stain), culture (can assess drug sensitivity) (takes up to 6 weeks). Low sensitivity.
sputum smear - 3 specimens needed inc an early morning sample, stained for present of acid fast bacili (AFB). All mycobacteria are ‘acid-fast’ including M. tuberculosis. If AFB are seen, treatment should be commenced and the patient isolated (in hospital only if clinical indication, or public health reason for admission; or at home).
nucleic acid amplification test (NAAT) - Direct detection of M. tuberculosis in sputum by DNA or RNA amplifi cation. Rapid diagnosis (<8hrs). Can also detect drug resistance
CT, lymph nodes, pleural biopsy, sampling of other affected systems:(e.g. CSF).
CXR for latent TB
primary - peripheral consolidation, hilar lymphadenopathy
miliary - fine shadowing
Fibronodular/linear opacities in upper lobe (typical), middle or lower lobes (atypical)
post-primary - upper lobe shadowing, streaky fibrosis and cavitation, calcification, pleural effusion, hilar lymphadenopathy
why gets Tb testing
close contacts of those with pulmonary or laryngeal TB, those with immune dysfunction, healthcare workers, and high-risk populations, eg prison, homeless, vulnerable migrants.
Ix for extrapulmonary TB
investigate for co-existing pul disease
Obtain material from aspiration or biopsy (lymph node, pleura, bone, synovium, GI/GU tract) to enable AFB staining, histological examination (caseating granuloma) and/or culture.
•NAAT can be carried out on any sterile body fluid, eg CSF, pericardial fluid.
