TB

Question 1

Key points about TB

Answer 1

• Risk factors: Hx of TB exposure, foreign born, HIV infection/immunosuppression, fibrotic changes on CXR associated w/ prior TB, high risk populations (IVDU, homeless, health care workers, elderly)
• Primary TB: infection w/ TB of someone who previously was never infected w/ TB
• Latent TB is a primary TB infection in someone who is ASx
• Post primary lesions occur from reactivation of a previously silent infection
• Reactivation of TB causes active pulmonary TB and can cause extra pulmonary TB

Question 2

Symptoms of active TB

Answer 2

• Fever, night sweats, weight loss, cough and hemoptysis

- Although many individuals will have minimal Sx

Question 3

Dx of TB

Answer 3

• Clinical features, CXR abnormalities (apical infiltrates often seen in active TB)
• Latent bacteria reside in lower lungs, active bacteria colonize apical lungs
• Demonstration of acid-fast bacilli/positive for ziehl-neelsen stain (smear and culture) in sputum or other fluids, possibly PCR
• Latent TB Dx by PPD test or Interferon gamma release assays
• Latent TB Rx w/ isoniazid for 9 mo

Question 4

Pathogenesis of TB

Answer 4

• Transmission via inhalation of infected droplets, bacteria phagocytosed by pulm macrophages and leading to a delayed hypersensitivity (type 4) reaction
• This will cause PPD tests to be active, about 6-8 wks after primary infection
• Primary infections are usually latent, and active infections usually occur during immunosuppressed states, old age, or from large inoculations

Question 5

Primary vs reactivated TB

Answer 5

• Primary TB often occurs in children, it usually affects the lower/middle lungs (indicates a recent transmission) and heals w/ no clinical Sx (fibrosis and calcification)
• Reactivated TB usually involves the upper lobes and can see small granulomatous broncho-pneumonic infiltration (+/- caseation)
• There can be bronchogenic spread to other areas of the lung, sub pleural lesions can extend into pleural cavity and cause effusion and/or empyema
• Leads to upper lobe destruction, fibrosis, hemoptysis

Question 6

Extrapulmonary TB

Answer 6

• Miliary TB: hematogenous spread of TB resulting from a caseous LN eroding a blood vessel
• Sx are insidious: malaise, fever, weight loss, sweats, meningeal signs in peds, splenomegaly, choroidal tubercles of retina
• Dx usually made by CXR (diffuse miliary pattern: global fuzzy white infiltrates) and sputum/blood positive for AFB
• TB meningitis: usually from hematogenous spread, typical meningitis Sx
• CSF shows increased pressure, reduced glc, leukocytosis (lymphocytic predominant), cultures are usually positive for AFB

Question 7

PPD

Answer 7

• Result >5 mm: considered positive if known HIV pt, recent contact w/ person that had active TB, fibrotic changes on CXR, pts who had organ Tx or are immunosuppressed
• Result >10mm: positive if 1 risk factor present and almost always means positive in LA, since living in LA is a risk factor
• Other risk factors: IVDU, chronic medical conditions, 4 yrs or younger, recent immigration, resident/employer of crowded setting
• If result is >15mm its positive for anyone

Question 8

Rx for TB

Answer 8

• Latent TB is Rx w/ daily isoniazid (INH) for 9 mo
• Active TB is Rx w/ 4 drug regimen (unless a strain of multi drug resistant TB- MDRTB): INH, rifampin, ethambutol, pyrazinamide for 2 months followed by INH and RIF for 4 months
• Poor adhesion or shorter duration will increase risk of developing MDR TB
• Side effects of TB Rx: hepatitis from INH, RIF, and PZA, optic neuritis (decreased red/green vision) from ethambutol, orange body fluids from RIF, ototoxicity/renal toxicity if using an aminoglycoside

Question 9

Nontuberculosis mycobacterium (NTM)

Answer 9

• Morphotype: middle aged white female, slender and tall w/ scoliosis and mitral valve prolapse
• Higher percentage of CFTR gene mutations
• Ex of atypical mycobacterium: mycobacterium avium complex (MAC)
• Variable presentation of MAC: COPD, no previous lung disease, hot tub lung, HIV, IL12/g-INF defects
• Mycobacterium leprae (leprosy) also an example, most common in tropical countries
• Mycobacterium marinum: associated w/ water (fish tank granuloma)
• Mycobacterium fortuitum: associated w/ nail salons (foot baths) and ear piercing

Question 10

BCG vaccine

Answer 10

-Vaccine against M bovis which will stimulate the body to create antibodies to mycobacteria

Question 11

Micro lab for TB

Answer 11

• At least 3 sputum samples to Dx TB, may need to do BAL (bronchoalveolar lavage)
• Add vit B6 to TB Rx to minimize side effects
• If MDR TB then can use streptomycin/aminoglycosides and/or fluoroquinolones