Saturday, March 15, 2008

TB made EZ

Tuberculosis is one of the world's most beatable disease, yet remains one of the biggest killers. It also can be a killer on the NCLEX or USMLE, as these tests commonly have questions related to this infectious disease. Common subjects include the diagnostic tests and antibacterial drugs used in treatment. Lets take a quick look at this subject, and see if we can make TB EZ.

Tuberculosis

•Most common cause of death due to infection worldwide
•Bacteria are unique for their ability to form granulomas in oxygen rich areas of lungs (often the apices due to the higher O2 levels) to protect themselves from elimination
•May stay dormant for years, becoming active w/any insult to immunity
•Spread by droplets (droplet precaution taken) and only contagious when active
S/S: Fever, night sweats, weight loss, malaise, and hemoptysis (bloody cough)
DX:
  1. • PPD: (+) if above or = 10cm in at risk or above or = 5cm in HIV, transplant, contacts (indicates exposure); The only patients that are + with above 15mm are those that shouldn't have been tested (no risk); Send for CXR if (+)
  2. • CXR: (-) take INH 9 mos; Send for BAL if (+) CXR (indicates previous infection)
  3. • BAL: (-) take INH 9 mos; (+) start 4 drug treatment protocol as resistance severe with Mycobacterium (indicates active infection)
Treatment Protocol: (with most common side/adverse effect)
  • Drug susceptibility test should be performed initially with culture
  1. Isoniazid (INH): Hepatotoxicity
  2. Rifampin: Red urine/tears/sputum/sweat
  3. Pyrazinamide (PZD): Uricemia/Stones in P
  4. Ethambutol: Blindness in Eyes (OR) Streptomycin: Ototoxic, Nephrotoxic
•Length of treatment can be long (up to 2 years) so patient compliance is a HUGE issue and number one cause of Antibiotic resistance present today.
•Stress to patient the fact that compliance to full regime has more than 90% cure rates, but must take meds everyday at same time!

PPD: Measure induration (redness) not just swollen area to detect if exposure has occurred.
Bottom picture shows Chest Xray with Granulomas (cavities) caused by previous TB infection


BAL: Bronchoalveolar lavage or bronchoscopy is the ONLY way of truly diagnosing TB. Think of Bigfoot...no matter how many pictures we have seen of someone that supposedly saw bigfoot, the only way to prove he exists is to capture him. Same way for infectious disease...the only truly positive diagnosis is to capture the bugs and grow them on a culture plate. So don't let them trick you on the test by saying a Positive ppd or chest xray means the patient has TB. Only then do we treat them with the 4 drug combo.

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