Reactivation Pulmonary Tuberculosis
- Initial pulmonary infection with M. tuberculosis, termed primary pulmonary tuberculosis, is often subclinical due to an effective cell-mediated immune response which sequesters infected foci within granulomas (See: Primary Pulmonary Tuberculosis). However, organisms within granulomas are never completely eliminated and can cause severe pulmonary disease years later when cell-mediated immunity wanes, especially in the elderly. It should be pointed out that for most patients the organisms stay dormant and only a small minority of individuals ever suffer reactivation, even in their elder years.
- Reactivation of Pulmonary Tuberculosis often begins insidiously with non-specific constitutional symptoms such as fever, anorexia, weight loss, and characteristically night sweats. Cough is common, may be non-productive initially but eventually purulent sputum is observed which may be blood-tinged. Progression involves expansion of necrotic areas within the lung parenchyma that erode into airways and pulmonary blood vessels. Erosion into airways drains the necrotic material leaving cavities that can be observed on chest radiography as radiolucent circles referred to as "Cavitations". Erosion into vasculature can lead to hemorrhage and is manifested as frank hemoptysis. Disease progression may be rapid in some, leading to severe debilitation in weeks or months whereas other patients progress slowly, a situation historically termed "Consumption". In cases of severe deficiency of cell-mediated immunity, disseminated infection may appear resulting in signs and symptoms of extrapulmonary tuberculosis.
- Although foci of primary pulmonary tuberculosis favor the lower and middle lung lobes since infective respiratory droplets tend to deposit there, reactivation favors the upper lung lobes especially within the lung apex. This is likely due to the higher oxygen tension in these upper pulmonary segments, as discussed in ventilation-perfusion ratio distribution, which facilitates growth of the obligate aerobe M. tuberculosis.