1
PULMONARY TB
ETIOLOGY
M. tuberculosis, is the most important cause of tuberculosis disease in
humans.
bacilli are non-spore-forming, nonmotile, weakly gram-positive curved
rods obligate aerobes that grow in synthetic media containing glycerol as
the carbon source and ammonium salts as the nitrogen source
(Loewenstein-Jensen culture media).
A hallmark of all mycobacteria is acid fastness
-
Growth 3–6 wk
,
drug susceptibility testing 4 wk
.
-
Growth can be detected in 1–3 wk in selective liquid medium
using radiolabeled nutrients (the BACTEC radiometric system
.)
-
rapid test by nucleic acid amplification (NAA) tests(PCR
.)
EPIDEMIOLOGY
Latent tuberculosis infection (LTBI) :-occurs after the inhalation of infective
droplet nuclei containing M. tuberculosis. A reactive tuberculin skin test
and the absence of clinical and radiographic manifestations
.
tuberculosis ( disease):- occurs when clinical or radiographic changes
become apparent. Untreated LTBI 40% → tuberculosis
2
Transmission
person to person, airborne mucus droplet nuclei, particles 1–5 μm in diameter that
contain M.TB
The chance of transmission increases
1-patient has an acid-fast smear of sputum
-
extensive upper lobe infiltrate or cavity
2-
-
3-copious production of thin sputum
-
4-severe and forceful cough
-
Environmental factors( poor air circulation
)
5-
Most adults no longer transmit the organism within 2 weeks after
adequate chemotherapy
person to person, airborne mucus droplet nuclei, particles 1–5 μm in
diameter that contain M.TB
The chance of transmission increases
:
-
-
patient has an acid-fast smear of sputum
.
-
extensive upper lobe infiltrate or cavity
.
-
copious production of thin sputum
.
-
severe and forceful cough
.
-
Environmental factors( poor air circulation
.)
Most adults no longer transmit the organism within 2 weeks after
adequate chemotherapy
3
PATHOGENESIS
The primary complex of tuberculosis includes
local infection and the regional lymph nodes
.
The lung is the portal of entry in >98% of cases
.
The tubercle bacilli multiply initially within alveoli and alveolar ducts
..
The tissue reaction in the lung parenchyma and
lymph nodes intensifies over the next 2–12 wk as
the organisms grow in number and tissue
hypersensitivity develops
Immunity
tubercle bacilli replicate
Cell-mediated immunity develops 2–12 wk after infection, along with
tissue hypersensitivity
.
mycobacterial antigen load
;
cell-mediated immunity, which enhances intracellular killing& tissue
hypersensitivity which promotes extracellular killing
.
heals completely by fibrosis or calcification Occasionally
:
-
focal pneumonitis and pleuritis, cavity , collapse-consolidation or
segmental lesion
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Pregnancy and the Newborn
Congenital tuberculosis is rare
.
A- lesion in the placenta through the umbilical vein
.
B- aspiration or ingestion of infected amniotic fluid
.
C- the most common route of infection for the neonate is postnatal airborne
transmission from an adult with infectious pulmonary tuberculosis
The Mantoux tuberculin skin test
-
is the intradermal injection of 0.1 mL(5 tuberculin units) of purified
protein derivative (PPD
.)
-
induce induration through local vasodilatation, edema, fibrin deposition,
and recruitment of other inflammatory cells to the area
.
-
The amount of induration should be measured by a trained person 48–72
hr after administration
.
-
Tuberculin sensitivity develops 3 wk to 3 mo—most often in 4–8 wk—
after inhalation of organisms
.
Y interferon
CLINICAL MANIFESTATIONS AND DIAGNOSIS
Tuberculosis infection :- no signs or symptoms, Occasionally, low-grade
fever and mild cough
.
Primary Pulmonary Disease
The primary complex includes the parenchymal pulmonary focus and the
regional lymph nodes
.
About 70% of lung foci are subpleural, and localized pleurisy is common
5
The usual sequence is hilar lymphadenopathy, focal hyperinflation, and
then atelectasis. collapse-consolidation or segmental TB . endobronchial
tuberculosis . lobar pneumonia , thin-walled primary tuberculosis cavity
>
55
%
of infants and children have no physical finding
.
Nonproductive cough and mild dyspnea , fever
,
night sweats, anorexia, decreased activity
,
failure-to-thrive
.
Occasionally residual calcification of the primary
focus or regional lymph nodes
.
The appearance of calcification ( least 6–12 mo
)
Diagnosis
isolation of M. tuberculosis (for culture and smear staining
:)
-
-
Sputum specimens
-
Induce sputum with a jet nebulizer and chest percussion followed
by nasopharyngeal suctioning (1 mo
.)
-
in young children is the early morning gastric acid obtained before the
child has arisen
.
3
consecutive morning gastric aspirates yield the organisms in <50% of
cases
Negative cultures never exclude the diagnosis of tuberculosis in a child
.
positive tuberculin skin test +abnormal chest
radiograph consistent with tuberculosis + history of
contact→TB
.
6
Miliary tuberculosis
usually complicates the primary infection,2–6 mo
.
most common in infants & young children
,
malnourished or immunosuppressed patients
.
Lesions are more numerous in the lungs, spleen
,
liver, and bone marrow than other tissues
.
Fever, wt loss, anorexia, Lymphadenopathy
,
hepatosplenomegali, Resp. feature late
.
. Biopsy of the liver or bone marrow with appropriate
Diagnosis
bacteriologic and histologic examinations more often yields an
early diagnosis
.
CXR miliary pattern 2-3 mm nodules
Perinatal TB
2nd-3rd week
-
fever, resp. distress, poor feeding
-
FTT
.
Lymphadenopathy, hepatosplenomegali
-
CXR hilar& mediastinal LN, lung infilterate
.
DD congenital infection
.
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Treatment
The standard therapy of intrathoracic tuberculosis is a
•
6
mo : isoniazid and rifampin + pyrazinamide in
the 1st 2 mo .100%
•
Nine month regimens of isoniazid and rifampin
.
INH resistance recommend adding a 4th drug—usually streptomycin, ethambutol, or
ethionamide—to the initial regimen
.
DOT directly observed therapy
intermittent (twice weekly) administration of drugs after an initial period as short as
2 wk of daily therapy is as effective in children as daily therapy for the entire course
.
LATENT TUBERCULOSIS INFECTION
9 mo of isoniazid, once a day
If daily therapy is not possible, DOT twice a week can be used for 9 mo
rifampin, once a day
Supportive Care
.
adequately treated
.
Adequate nutrition
Prevention
BCG is 50% effective in preventing pulmonary tuberculosis
.
The protective effect for disseminated and meningeal tuberculosis is
slightly higher, with BCG preventing 50–80% of cases