Flashcards in TB Consensus Deck (69)
Active TB disease caused by bacteria that are resistant to atleast 2 of the most commonly used drugs for treatment (ie INH and Rifampin)
Multidrug-resistant TB (MDR-TB)
TB caused by MDR strains that are also resistant to a fluoroquinolone and to at least one second-line injectable agent (amikacin, kanamycin, and/or capreomycin)
Extensively Drug-Resistant TB (XDR-TB)
What are the known virulence factors of M. tuberculosis?
cord factor (trehalose dimycolate), sulfatides, lipoarabinomannam (LAM)
cord factor - responsible for morphologic appearance of cells serpentine cords, assoc with ability of cells to produce disease
sulfatides - inhibit fusion of secondary lysosomes with bacilli-containing phagosomes within a macrophage
LAM- stimulates cytokine release from mononuclear cells
What is the doubling time of M. tuberculosis?
slow doubling time: 18-24 hrs
Culture is the gold standard for diagnosis of TB
1. Which method allows for visualization of colony but with prolonged time of growth (3-4 wks) and low sensitivity?
2. Which method allows for rapid detection (5-12 days) and susceptibility testing, increased sensitivity, and has the ability to distinguish MTBC from other species?
A. conventional culture
B. BACTEC TB System
- the only disadvantage of the BACTEC system is its radioactivity and its consequent expensive disposal
Of the following, which are the key elements in the primary defenses against TB?
b. NK cells
c. T lymphocytes
e. B lymphocytes
C and F - T lymphocytes and macrophages
T lymphocytes produce pro-inflammatory cytokines that enhance macrophage intracellular killing
macrophages- phagocytosis, intracellular killing, cytokine production, and antigen presentation to T cell populations
What kind of hypersensitivity reaction is seen in the tuberculin skin test?
Delayed-type hypersensitivity reaction (Type IV)
- cells mediating this reaction are CD4-positive, producing mostly TH1 cytokines
Which immunologic reaction causes caseous necrosis?
Delayed type hypersensitivity reaction (DTH)
- local macrophages and nearby tissues die
- DTH and CMI (cell-mediated immunity) develop in the third stage of TB immunopathogenesis
At what stage of the immunopathogenesis of TB are the following lesions formed?
a. caseous necrosis
b. hematogenous spread
c. tubercle/granuloma formation
d. cavity formation
A. Stage 3
B. Stage 4
C. Stage 2
D. Stage 5
Stages of TB:
Stage 1: Macrophage ingestion of TB bacillus
Stage 2: Stage of symbiosis, unrestrained replication; TUBERCLE/GRANULOMA
Stage 3: Increase in # of bacilli, devt of CMI and DTH; CASEOUS NECROSIS
Stage 4: a) enlargement of tubercle/caseous center, HEMATOGENOUS SPREAD
Stage 4: b) stabilization and regression of tubercle
Stage 5: caseous center liquefaction, extracellular bacillary growth; CAVITY FORMATION
This lung lesion is seen on primary TB, usually located in the subpleural area of the upper segment of the lower lobe or lower segment of upper lobe. It consists of the primary pulmonary focus, infected lymph nodes, and associated lymphangitis
- in most instances, the primary infection is controlled, with a positive TST as the only evidence of infection
- lesions of the Ghon complex heal by shrinkage, fibrous scarring, and calcification
What is the most clinically important form of disseminated TB analogous to bacterial sepsis?
- occurs when a caseous focus erodes into a blood vessel wall causing massive number of bacilli released into the bloodstream
In Wallgren's Timetable of Tuberculosis, disease progression of TB was described, intially marked by a febrile period. How long does it take for the following complications to occur after initial infection?
a. Renal TB
b. miliary or meningeal TB
c. TB of bones and joints
a. Renal TB - 5-25 yrs
b. miliary or meningeal TB - 2-6 mos
c. TB of bones and joints- 1 yr
What are the lung findings suggestive of cavitation?
crepitant rales and decreased breath sounds over affected areas
What is the most common form of extrapulmonary TB in children?
Scrofula (TB adenitis)
- since cervical lymph nodes may be normally palpated in young children, diagnosis should be supported by a + TST and other criteria for diagnosis, eg excisional bx and culture or FNAB if indicated
- firm, painless, discrete and movable
- if untreated, it may either resolve or prigress to necrosis and caseation of the LN, and result in a draining sinus tract (scrofuloderma)
What is the most common type of TB of the nervous system?
- usually involves CN III, VI, VII, optic chiasm, basal cisterns -- usually leads to papilledema and HCP
What is the radiographic hallmark of initial disease in TB
Relatively large size of adenitis compared with the relatively insignificant size of the initial focus in the lungs
What is the most common chest radiograph findings in childhood TB?
lymphadenopathy and parenchymal abnormalities
Which lymph nodes in the lung are most often affected by primary TB?
the nodes in the right upper paratracheal area
- since the lymphatic drainage of the lungs occurs predominantly from left to right
Should PTB treatment be initiated in an asymptomatic child with findings of hilar adenopathy on chest radiograph?
Not yet. Since hilar adenopathy has very low specificity (36%), it should not be the sole basis for initiating treatment.
When is radiographic clearing expected to occur after institution of therapy for TB?
6 mos to 2 yrs after institution of therapy
- in the first three mos of treatment, worsening of radiographic findings may be observed in 1/3 of pediatric pxs
Lesions in chronic pulmonary TB tend to localize in which part of the lung?
apical and posterior segments of the upper lobes, involving the right lung more than the left
- lymph node enlargement is no longer a feature
What is the most common radiographic manifestation of reactivation pulmonary TB?
local exudative TB
- focal or patchy heterogeneous consolidation involving the apical and posterior segments of the upper lobes and the superior segments of the lower lobes
What is the radiologic hallmark of reactivation TB?
What is the most diagnostic radiological change in pulmonary TB during infancy and childhood?
"millet-seed" densities of miliary TB
What is the PHEMISTER Triad, which is characteristic of TB arthritis?
1. juxtaarticular osteoporosis
2. peripherally located osseus erosions
3. narrowing of interosseus space
How is rheumatoid arthritis radiographically differentiated from TB arthritis?
- relative preservation of the joint space is also highly characteristic of TB arthritis
- early loss of articular space is more typical of rheumatoid arthritis
In a non-contrast and enhanced CT, what is the most specific finding in the diagnosis of CNS TB?
basal cistern hyperdensity
What is the most common complication of TB meningitis?
Which cranial nerves are commonly affected in cases of TB meningitis?
cranial nerve 2,3,4, and 7