Tuberculosis Flashcards
what bacterium causes TB
mycobacterium tuberculosis
- rod shaped bacilli
what stain is used to detect TB
Zeihl-Neelson stain
- waxy coat of mycobacterium tuberculosis prevents use of gram stain – known as “acid fast bacilli”
what colour does mycobacterium tuberculosis stain on a Zeihl-Neelson stain
red
how is TB spread
respiratory transmission
what are the stages of TB
primary infection
latent disease
secondary infection
miliary TB
what happens in primary TB infection
primary infection enters the lungs – formation of Gohn focus + spread to lymph nodes
what is a Gohn focus
lung lesion composed of tubercle- laden macrophages seen in primary TB
what kind of necrosis is there in TB
caseous necrosis
what is latent TB
immune system encapsulates sites of infection and stops progression of the disease
what is secondary TB
latent TB becomes reactivated due to the host becoming immunocompromised
where does secondary TB most commonly occur
apex of the lungs
what things can trigger secondary TB
immunosuppressive drugs e.g. steroids
HIV infection
malnutrition
what is miliary TB
Infection has disseminated in blood/lymphatics to cause multi organ disease
where does TB most commonly affect
the lungs
- 60% of TB cases
how does pulmonary TB present
chronic productive cough (+/- haemoptysis) systemic symptoms: - fever / night sweats - weight loss - malaise
what is the second most common presentation of TB
what are the symptoms?
genitourinary TB
- dysuria, loin/back pain, haematuria
what is Potts disease
TB affecting the spine
features of cutaneous TB
lupus vulgaris
erythema nodosum
erythema multiforme
what is the most serious complication of TB
TB meningitis
first line investigation for TB
chest XRAY
signs of primary TB on CXR
Ghon focus with ipsilateral hilarious lymphadenopathy
pleural effusion
signs of secondary TB on CXR
Cavitating lesion in apices
signs of miliary TB on CXR
diffuse 1-10mm shadows throughout lung fields
how many sputum samples are needed for microbiology
3
what tests are done on the sputum samples
microscopy, culture, sensitivities
- Zeihl-Neelson stain
- Nucleic acid amplification test (NAAT) can replace standard culture for earlier result if patient at high risk complications
- PCR for rifampicin resistance
what is a Mantoux test
tuberculin skin test
- indicates active/latent TB or previous BCG vaccination
- induration of 5mm or more = +Ve and patient should be assessed for active disease
what is an interferon-Gamma release assays
measures T cell response to TB antigens
- if person has had previous contact with TB then WBCs will release interferon gamma = positive result
what is the treatment for active TB
RIPE: Rifampicin (6 months) Isoniazid (6 months) Pyrazinamide (2 months) Ethamnutol (2 months)
what drug should also be co-prescribed in active TB treatment
pyridoxine (vit B6) to prevent peripheral neuropathy caused by isoniazid
how are patients with meningeal TB treated
further 6 months of rifampicin + isoniazid plus steroids
treatment of latent TB
3 months of rifampicin + isoniazid
or 6 months isoniazid
(+ pyridoxine)
what drug can cause red/orange discolouration of urine/tears
rifampicin
what drug can cause optic neuritis / colourblindness
ethambutol
what drug induces P450 system and so decreases effectiveness of oral contraceptive pill and warfarin
rifampicin
what drug can cause peripheral neuropathy
isoniazid
what drag can cause high uric acid levels and precipitate gout
Pyrazinamide
what drug can cause agranulocytosis
isoniazid
what drugs cause hepatitis
rifampicin
isoniazid
Pyrazinamide
