Emphysema is any air-filled enlargement in the body's tissues. Most commonly emphysema refers to the enlargement of air spaces (alveoli) in the lungs, and is also known as pulmonary emphysema. Emphysema is a lower respiratory tract disease, characterised by enlarged air-filled spaces in the lungs, that can vary in size and may be very large. The spaces are caused by the breakdown of the walls of the alveoli, which replace the spongy lung tissue. This reduces the total alveolar surface available for gas exchange leading to a reduction in oxygen supply for the blood. Emphysema usually affects the middle aged or older population because it takes time to develop with the effects of tobacco smoking, and other risk factors. Alpha-1 antitrypsin deficiency is a genetic risk factor that may lead to the condition presenting earlier. When associated with significant airflow limitation, emphysema is a major subtype of chronic obstructive pulmonary disease (COPD), a progressive lung disease characterized by long-term breathing problems and poor airflow. Without COPD, the finding of emphysema on a CT lung scan still confers a higher mortality risk in tobacco smokers. In 2016 in the United States there were 6,977 deaths from emphysema ¨C 2.2 per 100,000 of the population. Globally it accounts for 5% of all deaths. A 2018 review of work on the effects of tobacco and cannabis smoking found that a possibly cumulative toxic effect could be a risk factor for developing emphysema, and spontaneous pneumothorax. There are four types of emphysema, three of which are related to the anatomy of the lobules of the lung ¨C centrilobular or centriacinar, panlobular or panacinar, and paraseptal or distal acinar emphysema ¨C and are not associated with fibrosis (scarring). The fourth type is known as paracicatricial emphysema or irregular emphysema that involves the acinus irregularly and is associated with fibrosis. Though the different types can be seen on imaging they are not well-defined clinically. There are also a number of associated conditions including bullous emphysema, focal emphysema, and Ritalin lung. Only the first two types of emphysema ¨C centrilobular and panlobular ¨C are associated with significant airflow obstruction, with that of centrilobular emphysema around 20 times more common than panlobular. Centrilobular emphysema is the only type associated with smoking. Osteoporosis is often a comorbidity of emphysema. The use of systemic corticosteroids for treating exacerbations is a significant risk factor for osteoporosis, and their repeated use is recommended against.

Reference
Wiki: Pulmonary emphysema