Pocket Medicine: The Massachusetts General Hospital Handbook of Internal Medicine (89 page)

Microbiology & natural history

• Transmission of
Mycobacterium tuberculosis
via small-particle aerosols (droplet nuclei) • 90% of infected normal hosts will never develop clinically evident disease • Localized disease: healing & calcification
or
progressive 1° TB (at site of infection) • Hematogenous spread: latent infection ± reactivation TB
or
progressive dissem. TB

Screening for prior infection

•
Whom to screen
: high-prevalence and high-risk populations (HIV
Pts should have PPD testing as part of initial evaluation and annually thereafter) •
How to screen
: Mantoux tuberculin test (ie, purified protein derivative or PPD) inject 5-TU (0.1 mL) intermed. strength PPD
intradermally
→ wheal; examine 48–72 h •
How to interpret PPD
: determine max. diameter of induration by palpation

•
IFN-
γ
release assays (IGRA)
: (Ag-stimulated IFN-g release from Pt’s T-cells): can be used for screening where you would use PPD (
MMWR
2010;59:1); ↑ Sp, esp. in BCG Rx’d Pts (
Annals
2008;149:177). Does not distinguish active vs. latent, or recent vs. remote infxn. Relies on host immune fxn; Se limited in immunosupp. Lack of gold standard for latent TB infxn compromises Se/Sp estimates (
J Clin Epi
2010;63:257;
CID
2011;52:1031).

Clinical manifestations

•
Primary TB pneumonia
: middle or lower lobe
consolidation
, ± effusion, ± cavitation •
TB pleurisy
: can occur w/ primary or reactivation. Due to breakdown of granuloma w/ spilling of contents into pleural cavity and local inflammation.
Pulmonary effusion
± pericardial and peritoneal effusions (tuberculous polyserositis).

•
Reactivation TB pulmonary disease
: apical infiltrate ± volume loss ± cavitation •
Miliary TB
: acute or insidious; due to widespread hematogenous dissemination; usually in immunosupp, DM, EtOH, elderly or malnourished.
Constitutional sx
(fever, night sweats, weight loss) usually prominent. Pulm disease w/ small millet seed-like lesions (2– 4 mm) on CXR or chest CT (latter more Se) present in 60–80% of those w/ miliary TB.

•
Extrapulmonary TB
: lymphadenitis, pericarditis, peritonitis, meningitis, nephritis ± sterile pyuria, osteomyelitis (vertebral = Pott’s disease), hepatitis, splenitis, cutaneous, arthritis •
TB and HIV
: HIV
at ↑ risk infxn, progressive 1° infxn and reactivation. Risk of progression from infxn to disease >8–10%/y, higher risk with ↓ CD4. Reinfection (also w/ MDR) significant, esp. in hyperendemic areas.

Diagnostic studies for active TB
(
high index of suspicion is key!
)

•
AFB smear
(rapid dx) and
culture
(↑ Se & allows sensitivity testing) of sputum, BAL, pleura, etc.;
avoid FQ
if considering TB (can compromise dx yield) • PCR: 94–97% Se c/w smear; 40–77% Se c/w culture (
JAMA
2009;301:1014) • CXR: classically fibrocavitary apical disease in reactivation vs. middle & lower lobe consolidation in 1° TB, but distinction imperfect. HIV
assoc. w/ non-apical disease regardless of timing (
JAMA
2005;293:2740).

• Adenosine deaminase testing: useful in extrapulmonary sites, best validated for ascites
Preventive therapy
(
Annals
2009;150:ITC6-1;
NEJM
2010;362:707)

• Prophylaxis reduces incidence of subsequent disease by 65–75%

• Treat Pts who are
based on guidelines listed above or any exposed HIV
or immunocompromised Pt •
R/o active disease
in any Pt w/ suggestive s/s before starting INH. If HIV
, routinely ask if cough, fever or night sweats; if yes → ✓ sputum smear, CXR, CD4

• ✓ LFTs monthly (risk ↑ w/ age;
Chest
2005;
1
28:
11
6
): if 5× ULN
or
sx → stop TB meds & reeval

Treatment of active tuberculosis
(
Annals
2009;150:ITC6-1;
NEJM
2013;368:745)

• Isolate Pt per infection control if hospitalized, modified isolation per Dept of Health if outPt • Use multiple drugs (see below) to which organism susceptible; consult ID before empiric Rx if possible MDR-TB (suspect if prior TB Rx, from or travel to area w/ ↑ rates of MDR, exposure to person w/ likely MDR-TB, poor Rx adherence) or if INH resistance in community ≥4% (includes most of U.S.), extrapulm. TB or HIV
(
NEJM
2008;359:636) • Screen for HIV in Pts starting TB Rx; if HIV
, consult ID re: timing of concurrent HIV Rx • Promote adherence to Rx; directly observed Rx cost-effective if high risk for nonadherence • Obtain monthly smears/cx on treatment until 2 consecutive are
for TB