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)

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

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

• 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%

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

 

Treatment:

1^st: 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 2^nd line agents

 

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Download the PDF version: here

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References:

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