- What is the pattern of cellular injury in this case?
This is granulomatous inflammation. The microscopic appearance is consistent with caseous necrosis. The chest radiograph suggests dystrophic calcification (upper lobe calcifications).
- What caused this condition?
Infection with tuberculosis (the most common organism to produce this condition is Mycobacterium tuberculosis).
- What is the time frame for development of the lesions?
Granulomatous inflammation generally occurs over weeks to years. Lesions with calcifications are probably old lesions years old that have been contained by the body's immune response. Caseous necrosis suggests ongoing inflammation weeks to months old.
- What are the potential outcomes?
In most cases, TB infections are "subclinical" and occur without major symptomatology, because the immune system is able to contain the infection. Such persons may be detected by a positive TB skin test. A chest radiograph is performed to determine if lung disease is present. Just old calcifications suggest old, contained disease. More extensive lung injury could suggest ongoing infection and the need for treatment. Persons who are in poor health are more likely to have TB infection that is not contained.
- Why is it necessary to screen for persons who might have this condition?
TB is a public health problem because it is highly contagious. In the U.S., the public health strategy is to screen for, find, and treat infected persons to prevent further infections.
