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 -> if the patient has hx of close contact with TB, initiate treatment with INH + repeat test in 8-12 wks:
- If negative -> discontinue INH
- If positive -> continue INH for 9 mo (same as latent TB)Â
- 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%
- Interferon gamma release assay (IGRA): a blood test equal in significance to PPD to exclude TB exposure. No cross reaction w\ BCG
- Adenosine deaminase: useful in pleural TB (high NPV), possible meningitis TB, not for pulmn\extra pulmn
- 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 medicineÂ
- Toronto notesÂ
- Kaplan step 2 videos