Impact of the Biomechanical 'Pleural Stress' Pressure Vessel Hypothesis on the Pathogenesis of Tuberculosis: Predictors of TB Reactivation and its Application to TB Screening

Abstract

A hypothesis for the pathogenesis of pulmonary TB is presented based on the biomechanics of pleural stress in the context of the lung as a pressure vessel. This hypothesis modelled pleural stress as a marker of pleural tissue destruction and subsequent repair. It identified five predictors of TB reactivation, namely adolescent and young adult age, male gender, apical location, low antero-posterior chest diameter or low thoracic-index rib-cage shape and the presence of pre-existing apical blebs. This hypothesis is complete in that it explains the occurrence of apical lower lobe disease, the age, gender and build of those at risk, the incidence of concurrent apical disease and also Esmail's prediction about the size of the population at-risk of TB reactivation. Once a subject can be identified as having several of the biomechanical predictors of TB reactivation as explained by the pleural-stress pressure vessel hypothesis, initial screening can be performed based on demographics, Body Mass Index (BMI) and thoracic index. A second round of screening by imaging can confirm the presence of apical blebs or bullae with an expected pickup rate of approximately 15% of the screened group. It would therefore be possible to immunize, closely observe or treat this high-risk group. Low-cost, portable MRI has been suggested as a TB screening tool available in the near future as it promises to be a near ideal screening tool in that it is safe, can be delivered in a low-cost, mobile and portable manner using new and emergent Magnetic Resonance Imaging (MRI) technologies, with high sensitivity and specificity.