Mycobacterial Infections

Question 1

TB Pathogenesis

Answer 1

Bacilli reach alveolar space
Proliferation inside macrophages
Initial inflammatory granulomatous tubercle formation (if controlled here=latent infection)
Enlargement of tubercle and infiltration of lymph system (Gohn complex)

Question 2

Secondary/Reactivation Presents with

Answer 2

Cough, hemoptysis
Persistent fever/night sweats
Weight loss
Malaise
Adenopathy
Pleuritic chest pain

Question 3

Miliary Tuberculosis

Answer 3

denote ALL forms of progressive, widely disseminated hematogenous tuberculosis, even if the classical pathologic or radiologic findings are absent.

Question 4

Tuberculin Skin Testing

Answer 4

Positive tuberculin skin test does NOT by itself prove the presence of active disease but DOES indicate that infection has occurred
Primary use is in detection of Latent TB Infection
MUST be read at 48-72 hours
Test is read by the diameter of the induration, NOT the diameter of erythema
If patient is being tested shortly after exposure, repeat testing should be done in 6-12 weeks

Question 5

An induration of ≥ 5 mm

Answer 5

HIV positive persons
Recent contacts of TB case
Fibrotic changes on chest radiograph consistent with old TB
Patients with organ transplants and other immunosuppressed patients (Prednisone)

Question 6

An induration of ≥ 10 mm

Answer 6

Recent arrivals (<4 yr of age or infants, children, and adolescents exposed to adults in high-risk categories

Question 7

An induration of ≥ 15 mm

Answer 7

Persons with no risk factors for TB

Question 8

Mycobacterium Culturing

Answer 8

Gold standard for the diagnosis of tuberculosis

organism has slow growth rate

Question 9

Whole-blood interferon-gamma assay (e.g. QuantiFERON-TB Gold test)

Answer 9

Screening test for asymptomatic disease

Question 10

Rapid Nucleic Acid Assays

Answer 10

Can produce results within two to seven hours after sputum processing
generally recommended on all AFB smear-positive respiratory specimens

Question 11

Latent Tuberculosis Management

Answer 11

Generally the recommendation is nine months of Isoniazid (INH) monotherapy

Question 12

Reactivation TB Disease Management

Answer 12

Requires at least 2 effective drugs 
Several guidelines recommend that initial therapy of active tuberculosis is four drugs:
Isoniazid (INH)
Rifampin (RIF)
Pyrazinamide (PZA)
and Ethambutol (EMB)

Question 13

Isoniazid (INH)

Answer 13

MOA: Covalently binds to and inhibits enzymes essential for the synthesis of mycolic acid (key component of the cell wall)Hepatotoxicity, must monitor liver enzymes
***Most common side effect is peripheral neuritis which manifests as paresthesias and is associated with pyridoxine (vitamin B6) deficiency

Question 14

Rifampin (RIF)

Answer 14

MOA: Blocks transcription by interfering with the beta subunit of bacterial RNA polymerase
Hepatotoxicity, liver enzymes
Inducer of cytochrome P450

Question 15

Pyrazinamide (PZA)

Answer 15

Only seen in antitubercular combo packages
Extensively metabolized by the liver, must watch for hepatotoxicity!
Gout

Question 16

Ethambutol (EMB)

Answer 16

MOA: inhibits an enzyme important for the synthesis of the mycobacterial arabinogalactan cell wall
Optic neuritis which results in diminished visual acuity and loss of ability to discriminate between red and green