Tuberculosis

Microbiology:

Most common: Mycobacterium tuberculosis

Transmission:

Via inhalation of aerosolized droplets from sneezing\coughing pt w\ and active infec. (Pts w\ primary TB aren’t contagious)

TB 1.jpg

Types of tuberculosis infection:

a. PRIMARY TB:

  • In a prev unexposed\nonsensitized pts (usually children)
  • Ghon focus: sub pleural, at the lower part of upper lobe or upper part of lower lobe -> granuloma where the organism remains dormant after resolution of the primary infec
  • Only 5-10% of pts w\ primary -> develop active ds in their lifetime -> 50% of them w\in the first year
  • Clinical features: the majority are asx, mild fever, mild dry cough, erythema nodosum

 

b. SECONDARY TB:

  • When the center of the granuloma is discharged due to host’s weakened immunity (HIV, malignancy, immunosuppressant, substance abuse, poor nutrition)
  • Localized to the apices of one\both upper lobes (most oxygenated)

Clinical features:

    • Constitutional sx: fever (usually in the evening), night sweats, wt loss, malaise
    • Cough: early is dry -> progress to productive (purulent sputum)
    • Hemoptysis: mild (blood streaks) -> massive
    • Chest pain: dull ache due to pleurisy
    • Dyspnea: late sx. Due to fibrosis, pleural effusion, or spontaneous pneumothorax
    • Apical rales
TB 5
Upper lobe cavitation

CXR:

  • Upper lobes infiltrates + cavitation
  • Pleural effusion, pneumothorax, displaced trachea and heart towards lesion bc of fibrosis

 

c. EXTRA PULMONARY TB:

  • Primary\secondary -> unable to contain bacteria -> active ds throughout the body

Involves any organ:

  • LN: cervical > supraclavicular
  • Skeletal: vertebral osteomyelitis (Pott’s ds): thoracic > cervical > lumbar
  • Intestines (typically terminal ilium; mimics crohn’s)
  • CNS: meningitis (lymphocyte 50-500, H protein, L glucose), tuberculoma
  • GU: sterile pyuria, hematuria, genital epididymitis, salpingitis, endometritis

Miliary TB: acute diffuse dissemination of organism via blood

  • Develops in HIV, children, elderly
  • Organomegaly, reticulonodular infiltrates on CXR (miliary mottling), choroidal tubercles in the eye

 

Diagnosis:

1. Sputum studies:

  • At least 3 specimens, preferably early morning

» AFB smears:

  • 2 stains are used: Ziehl-Neelsen and fluorochrome
  • Quick dx, low sensitivity and specificity
  • Used to follow-up treatment efficacy

» Culture: Lowenstein-Jensen media, takes 4-8 wks

2. Tuberculin skin test (PPD test):

  • Screen exposed individuals, for latent TB, not for active ds

TB 11

  • If negative -> do another one 1-2 wks later
  • If positive -> do CXR to rule out active ds -> start 9 mo of INH

» Positive PPD has a 10% lifetime risk TB, INH results in 90% reduction of this risk; therefore, the risk after INH goes from 10 to 1%

  1. Interferon gamma release assay (IGRA): a blood test equal in significance to PPD to exclude TB exposure. No cross reaction w\ BCG
  2. Adenosine deaminase: useful in pleural TB (high NPV), possible meningitis TB, not for pulmn\extra pulmn
  3. Pleural biopsy: most accurate diagnostic test

 

Treatment:

1st: Rifampin, INH, Pyrazinamide, Ethambutol (RIPE)

  • First 2 months: 4 drug-regimen -> following 4 months: INH + rifampin = total of 6 months
  • Treatment is extended to 9 mo for: osteomyelitis, military TB, meningitis, pregnancy (whenever pyrazinamide isn’t used)
  • Rifampin, INH, Pyrazinamide are all hepatotoxic!

» MDR = resistance to INH + Rifampin

» XDR = resistance to INH + Rifampin + fluoroquinolone + ≥ 1 of injectable 2nd line agents

 


Download the PDF version: here


References:

  • Master the boards
  • Step up to medicine 
  • Toronto notes 
  • Kaplan step 2 videos

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