Types of tuberculosis(TB)
Types of tuberculosis(TB)
Pulmonary Tuberculosis has 3 main types
Miliary or(disseminated TB )
tuberculosis varies greatly in different populations*
improved living standards, population screening, immunization and effective drug therapy have very greatly reduced of all forms of tuberculosis.
Childhood tuberculosis or primary TB will become significantly rare.
The opportunistic fact of this disease*.
old latent lesions are liable to be activated by corticosteroid or other immunosuppressive therapy, by chronic alcoholism, the development of diabetes mellitus and in workers with silicosis.
In patients who have not previously had tuberculosis, inhalation of tubercle bacilli causes a primary or parenchymal lesion, also termed the ghon focus*.
This is usually single, 1-2 cm in diameter, and situated just beneath the pleura
other component of primary TB is the enlarged lymph node((hilar))
Both of it components are linked with lymphatics greatly enlarged and caseous.
This combinations is termed as Primmary complex it is much larger than a single ghon foci..
usually at the base of lungs, and ,caused by a very low dose of infection . Anatomically, the basal and middle zones of thelungs are more prone to infection than the apical zones becauseof their volume, although sometimes ventilation seems to befavoured in the latter.
Where is primary TB most active in??
How did they proof it??
It is supported by the findingof single calcified primary lesions observed in necropsies((autopsy)),in which 66% of infections were located in the lower half ofthe lung and only 12% were supraclavicular.
Also it takes 4 to 6 weeks to develop with a limited progress .
Ghon focus undergoes healing: if small, by fibrous tissue; if larger, the caseous centre usually persists and is converted into a hard calcified nodule Visible in chest radiographs...
How serious is it?
This primary complex resolves spontaneously withno symptoms in 95%* of infected people, but 5% develop the disease,which may be local (i.e.causing pleurisy when there is ruptureinto the pleural cavity) or systemic (i.e.causing meningealor even miliary TB).
Post primary TB result mainly from the reactivation of the latent lesion by the opportunistic fashion
reinfection way from an active case.
The re-infection lesion result from proliferation of mycobacterium tuberculosis in the wall of a bronchiole(activation of bronchial spared) or alveolus.
It was associated with elderly people
We can say that Post primary infection can be endogenous , resulting from reactivation of a dormant primary or post primary lesion, or it may be exogenous i.e. caused by organisms in inhaled dust, ets.
The common sites for post-primary pulmonary tuberculosis are the posterior or apical segment of the upper lobe & the superior segment of the lower lobe .
the anatomical location of the lesion is attributed to the good ventilation but relatively low blood flow in those areas.
During the primary tuberculosis infection or following BCG immunization, the patient develops cell-mediated immunity to antigens of the tubercle bacillus so antibody will be present either ways.**
So the result of tuberculin test will be +ve ,,
Radiographic images is required .
n anteroposterior X-ray of a patient diagnosed with advanced bilateral pulmonary tuberculosis. This AP X-ray of the chest reveals the presence of bilateral pulmonary infiltrate (white triangles), and caving formation (black arrows) present in the right apical region.The diagnosis is far-advanced tuberculosis.
The infection spreads by the lymphatics, but, because of the immune state it induces a delayed hypersensitivity
lymphatic spread is strictly localized. Because of the partial state of immunity which exists. Progress of the lesion is slow
tubercles are well developed and there is conspicuous formation of fibrous tissue at their periphery.
If healing does not now occur, some of the nodules will spread to involve the wall of a bronchus and blockage of the lumen follows.
the caseous material within the tubercle may be gradually discharged along the bronchus, leaving a small cavity.
Bronchial spread to the upper parts of other lobes and to the other lung may occur, and chronic pulmonary tuberculosis is frequently bilateral.
there is considerable overgrowth of fibrous tissue, in this way the lung shrinks and pulmonary and bronchial blood vessels involved in the wall of a cavity usually become occluded
Atelectasis will formed
wall of the artery may be weakened and rupture; serious and sometimes fatal hemorrhage results.
This is to be distinguished from the coughing up of blood-stained sputum.
when there has been breakdown of resistance and extensive bronchopneumonia
blood dissemination with acute military tuberculosis may occur
Tuberculosis ulcers may develop in the larynx or in the intestine from direct infection
Development of post primary TB
Generalized Miliary Tuberculosis
In developed country where the prevalence of tuberculosis is low, miliary tuberculosis occurs most commonly in the elderly. In contrast, where the prevalence of tuberculosis is high, it occurs most frequently in childhood.
Why it is called miliary??
BECAUSE it is a form of tuberculosisthat is characterized by a wide dissemination into the human body and by the tiny size of the lesions . Its name comes from a distinctive pattern seen on a chestX-rayof many tiny spots as a milletseeds shaped spots.
When it accure?
The pulmonary lesions are part of an acute generalized tuberculosis, which occurs when a large number of mycobacterial gain entrance to the bloodstream.
lesions are usually more numerous in the lungs than in any other organ like liver & spleen.
They consist of grey tubercles which may be too small to be visible by the naked eye or up to 3mm in diameter.
How the microorganism gets systemic?
tuberculosis infection in the lung result of erosion of the infection into a pulmonary vein. the bacteria reach the left side of the heart and enter the systemic circulation, the result may be to seed organs such as the liver and spleen with said infection. Alternately the bacteria may enter the lymph node(s), drain into a systemic vein and eventually reach the right side of the heart. From the right side of the heart, the bacteria may seed - or re-seed as the case within the lungs, causing the "miliary" appearance.
As a review