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Types Of Tuberculosis-TB-Primary and Secondary Tuberculosis

Tuberculosis is a chronic granulomatous disease caused by Mycobacterium tuberculosis. It does not only affects lungs, besides lungs it may also affects, Brain, Kidneys, Bones, GIT and other organs.

Types Of Tuberculosis:

Primary Tuberculosis:
Primary tuberculosis is the form of disease that develops in a previously unexposed and therefore unsensitized, person.
In this type the source of organism is exogenous and about 5% of newly infected develop significant disease.
In primary tuberculosis granulomatous lesions are formed at the site of infection due to delayed hypersensitivity reaction (immunological response).
A granuloma wall off the infected site and prevent the infective agent from spreading to the neighbouring sites and it heals by fibrosis and scarring. In the centre of granuloma, bacteria may remain alive and may infect the patient again later in life, in elderly or when he becomes immunocompromised. In primary tuberculosis the regional lymph node are more prominently involved.
In severely immunocompromised and malnourished  indviduals the disease may develop without interruption into Progressive Primary Tuberculosis.  In Progressive Primary tuberculosis, caseating granulomas are absent due to lack of tissue hypersensitivity reaction.

Secondary (post-primary) Tuberculosis:
Secondary tuberculosis is a pattern of disease that arises in a previously sensitized host. It may follow shortly after primary tuberculosis, but more commonly it arises from reactivation of dormant primary lesions many decades after initial infection, particularly when host resistance is weakened.
Secondary pulmonary tuberculosis is classically localized to apex of one or both lungs because of high oxygen tension in the apices.
In secondary tuberculosis, patient is already sensitized, therefore in such individual the tendency of walling off the infective site greater than those of primarily infected patients provided that the immune system of the patient is not compromised.  Hence, in such patients infection remain localized and regional lymph nodes are less commonly involved.
In secondary tuberculosis there are greater chances of spread of infection of the other organs that is, brain, kidneys and bones etc.

Pattern (Types) Of Secondary Tuberculosis:
l. Progressive Pulmonary Tuberculosis: 
Miliary tuberculosis. Small lesions are
visible on a radiograph
The apical lesion enlarges with expansion of area of caseation. Erosion in to the bronchus evacuates the caseating material and this results in spread of infection in other parts of the lungs and it may spread to other organs of body.

2. Miliary Pulmonary Tuberculosis. 
It occurs when organism enters into the lymphatics which empties in to the venous return to the right side of the heart and thence into the pulmonary arteries then to the all part of the lungs. This result in lesions either microscopic or small visible (2mm) foci of yellow-white consolidation scattered through the lung parenchyma.
Pleural effusions, tuberculous empyema and obliterative fibrous pleuritis are common complications of progressive disease.

3. Endobronchial, endotracheal and laryngeal tuberculosis:
Organisms spread to these sites and cause microscopic granulomatous lesions in the mucous membranes of these sites.

4. Systemic Miliary Tuberculosis. 
Organism may enter in the pulmonary venous return to the left site of the heart and from here it may spread to almost every organ of the body. Lesions resemble those of lungs.
The most common organs which may involve are; liver, bone marrow, spleen, adrenal, meninges, kidney, fallopian tubes and epididymis.

5. Isolated Organ Tuberculosis:
It may appear in any one of the organs or tissues seeded hematogenously.
when vertebrae are affected, the disease is referred to as pott disease.

7. Lymphadenitis:
It is the most frequent form of extra-pulmonary disease, usually occurring in the cervical region. The lymph nodes are swollen and tender. In HIV negative individuals lesions are uni-focal and there are no other signs. HIV positive individuals always demonstrate multi-focal disease, systemic symptoms, either pulmonary or other organ involvement by active tuberculosis.

8. Intestinal Tuberculosis.
It was common previously due to use of unpasteurized milk. Now it is uncommon in developed countries but in under-developed countries it is still present.
In developed countries it is more often a complication of protracted advanced secondary tuberculosis, secondary to the swallowing of coughed-up infected material
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