Investigations and Treatment Flashcards
what investigations should be done?
radiology
microbiological diagnosis
- microscopy of sputum using ZN stain
- culture on selective media
- PCR: direct from sample 1st line
- tuberculin skin test and IFNg if latent
what signs may be seen on a CXR?
upper lobe predominance
CXR consolidation with or without cavitation
fibrosis
calcification
Pleural effusion
widening of the mediastinum
why does a special stain need to be used for TB?
mycobacterium tuberculosis is acid alcohol fast bacilli and has a thick waxy coat
how is the stain obtained?
red dye (carbol - fuchsin) added to smear it is heated to allow dye to penetrate the waxy coat
acid/alcohol is added
Waxy coat of mycobacteria retain dye even after exposure to acid and alcohol
Non-waxy bacteria don’t (i.e other bacteria)
Counterstain added and Mycobacteria appear red
what is the advantages and disadvatages?
they are cheap(ish) and rapid
dis: no indication of species or sensitivity
what do the cultures require?
selective media - lowenstein jensen
what characteristics are identified on growth culture?
colour, speed, texture, biochemical characteristics
what are the disadvantages?
it is very slow growing but on the other hand it is very sensitive
what is a disadvantage of PCR?
it does not tell you if the organisms are alive or dead
what may give you a false -ve result on mantoux/ tuberculin skin test?
if previous BCG
if the mantoux is positive what test do you do?
IFN gamma
what do interferon gamma release assays detect?
T cell secretion of IFN g following exposure to tb specific antigens
what happens in response to re-exposure to TB specific antigens if the person has been infected with TB already
activated T cells within their extracted whole blood secrete quantifiable levels of IFNg
how is a diagnosis made for active TB?
if the CXR suggests TB, take sputum samples
(≥3, with one early morning sample, before starting treatment if possible) and send for MC&S for AFB (acid-fast bacilli resist acid on Ziehl–Neelsen (ZN) staining). If spontaneously produced sputum cannot be obtained, bronchoscopy and lavage may be needed.
how is adiagnosis made for active non-resp TB?
Try hard to get samples: sputum, pleura & pleural flu- id, urine, pus, ascites, peritoneum, bone marrow or CSF. Send surgical samples for culture. Microbiologist should routinely do TB culture on these, even if it is not re- quested. All patients with non-respiratory TB should have a CXR to find coexisting respiratory TB. Incubate cultures for up to 12wks on Lowenstein–Jensen medium.
what is the histological hallmark of TB?
presence fo caseating granulomata
Immunological evidence of TB?
may be helpful: Tuberculin skin test: TB antigen is injected intradermally and the cell-mediated response at 48–72h is recorded. A +ve test indicates immunity. It may also indicate previous exposure or BCG. A strong +ve test probably means active TB. False–ve tests occur in immunosuppression (miliary TB, sarcoid, AIDS, lymphoma). Quantiferon TB Gold® and T-spot-TB® tests measure the delayed hypersensitivity reaction developed after contact with M. tu- berculosis; they use specific, complex M. tuberculosis antigens and are better than older Mantoux tests, which rely on reactions to serial dilutions of TB antigen.1
what should be done if the histological and clinical picture indicate TB ?
start treatment without waiting for culture results and continue even if these are negative
contact tracing and public health notification are essential
what should be done before treatment starts ?
stress importance of compliance/concordance (helps the patient & pre- vents resistance). Test colour vision (Ishihara chart) and acuity before and during treatment as ethambutol may cause (reversible) ocular toxicity.
Check FBC, U&E, LFT.
If pre- creatinine clearance=10–50mL/min: Rifampicin: dose by 50%. Ethambutol: monitor U&E; avoid if possible. No dose change for ethionamide or isoniazid.
what is the treatment for the initial phase?
8 weeks on 4 drugs
need directly observed therapy
rifampicin, isoniazid, pyrazinamide, ethambutamol
what are the side effects?
Rifampicin SE: discolouration of urine/tears, hepatitis, flu-like illness, inactivation of the pill, decreased platelets
Isoniazid SE: decreased WCC, stop if neuropathy and give pyridoxine, agranulocytosis, allergic reaction
Pyrazinamide SE: hepatotoxicity (rare), reduced renal excretion of urate, gout
Ethambutol SE: colorblindness developing into blindness
what test is sensitive to rifampicin resistance
PCR
what happens in the continuation phase?
(16wks on 2 drugs) rifampicin and isoniazid at same doses
consider steroids if meningeal or pericardial TB
