TB Flashcards
what is TB?
caseating granulomatous inflammation
It is a chronic infection described in many body sites - the lungs, gut, kidneys, lymph nodes, skin…
describe the granulomas
they have a necrotic centre
surrounded by epitheliod cells and langerhans giant cells
you get the formation of Ghon focus
what type of hypersensitivity reaction is it?
type 4 - granulomas with necrosis
what factors affect the prevalence and risk of developing TB in the developed world
contact with high-risk groups
immune deficiency
lifestyle factors
genetic susceptibility
what immune deficiency may case problems ?
HIV infection
corticosteroids or immunosuppressant therapy
chemotherapeutic drugs
nutritional deficiency (vitamin D)
diabetes mellitus
chronic kidney disease
malnutrition/body weight > 10% below ideal
if CD4 is low and ESR is high
what lifestyle factors increase the risk?
drug/alcohol misuse
homelessness/hostels/overcrowding
prison inmates
what happens when the mycobacteria enters the body
T-cell response to organism enhances macrophage ability to kill mycobacteria
this ability constitutes immunity
what does the T cell response cause?
T-cell response causes granulomatous inflammation, tissue necrosis and scarring
this is hypersensitivity (type IV)
what is the pathology of primary TB?
1st exposure and up to 5 years later it causes an infection
what is the pathology of secondary TB?
reinfection or reactivation of disease in a person with some immunity
disease tends initially to remain localised, often in apices of lungs
can progress to spread by airways and/or bloodstream
where does secondary TB tend to affect?
often in the apices of the lungs initially but can progress to spread by airways and/or bloodstream
what tissue changes are indicated in primary TB?
small focus (ghon focus) in the periphery of the mid zone of lung
large hilar nodes (granulomatous) on the CXR
what tissue changes are indicated in secondary TB?
fibrosing and cavitating apical lesions
much more necrosis and tissue damage at the site of infection
what is an importatn diff. diagnosis for secondary TB?
cancer
what are the features seen with latent infection?
- bacillli present in ghon focus
- sputum smear and culture negative
- tuberculin skin test usually positive
- CXR normal (small calcified ghon focus frequently visible)
- asymptomatic
- not infectious to others
what are the features of active disease?
bacilli present in tissues or secretions
sputum commonly smear and culture positive in pulmonary disease
MTb can usually be cultured from infected tissue
Tuberculin skin test usually positive (and can ulcerate)
CXR shows signs of consolidation/ cavitatio/ effusion in pulmonary disease
symptomatic- night sweats, fever, weight loss and cough common
infectious to others if detectable in sputum
what is the ratio of extra:intra pulmonary disease in latent TB?
55% pulmonary
45% extrapulmonary
what are the respiratory symptoms of TB?
persistent productive cough (.3 weeks) and occasional haemoptysis
hoarseness
pleuritic pain
cough
haemoptysis
what are the general symptoms of TB?
weight loss, night sweats, fever fatigue
what are the meningeal symptoms of TB?
headache, drowsy, fits
what are the GI symptoms of TB?
peritonitis, perforation, bowel obstruction, pain
what are the signs of tb?
may hear upper zone crackles
