Emphysema
Emphysema is a condition of the lung marked by abnormal enlargement of the alveoli with loss of pulmonary elasticity. Most commonly, emphysema refers to the permanent enlargement of air spaces 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, 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 – 2.2 per 100,000 people. Globally it accounts for 3% 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 – centrilobular or centriacinar, panlobular or panacinar, and paraseptal or distal acinar emphysema – and are not associated with fibrosis. 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 – centrilobular and panlobular – 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.Signs and symptoms
Emphysema is a respiratory disease of the lower respiratory tract. It is commonly caused by tobacco smoking but some people are affected who have never smoked. The presence of emphysema is a clear risk factor for lung cancer, made stronger in those who smoke.
Early symptoms of emphysema vary. They can include a cough, wheezing, a fast breathing rate, breathlessness on exertion, and a feeling of tightness in the chest. There may be frequent cold or flu infections. Other symptoms may include anxiety, depression, fatigue, sleep problems and weight loss. These symptoms could also relate to other lung conditions or other health problems; therefore, emphysema is often underdiagnosed. The shortness of breath emphysema causes can increase over time and develop into chronic obstructive pulmonary disease.
A sign of emphysema in smokers is a higher number of alveolar macrophages sampled from the bronchoalveolar lavage in the lungs. The number can be four to six times greater in those who smoke than in non-smokers.
Emphysema is also associated with barrel chest.Types
There are four main types of emphysema, three of which are related to the anatomy of the lobules of the lung – centrilobular or centriacinar, panlobular or panacinar, and paraseptal or distal acinar and are not associated with fibrosis. Although fibrosis is not a normal feature of these subtypes, repair strategies in end-stage emphysema may lead to pulmonary fibrosis. The fourth subtype is known as paracicatricial emphysema or irregular emphysema, involves the acinus irregularly and is associated with fibrosis.
Only the first two types of emphysema – centrilobular and panlobular – are associated with significant airflow obstruction, with that of centrilobular emphysema around 20 times more common than panlobular. The subtypes can be seen on imaging but are not well-defined clinically.
There are also a number of associated conditions including bullous emphysema, focal emphysema, and Ritalin lung.Centrilobular
Centrilobular emphysema, also called centriacinar emphysema, affects the centre of a pulmonary lobule in the lung, the area around the terminal bronchiole and the first respiratory bronchiole, and can be seen on imaging as an area around the tip of the visible pulmonary artery. Centrilobular emphysema is the most common type usually associated with smoking, and with chronic bronchitis. The disease progresses from the centrilobular portion, leaving the lung parenchyma in the surrounding region preserved. Usually the upper lobes of the lungs are affected. The upper lobes of the lungs are more susceptible to centrilobular emphysema because of their higher ventilation:perfusion ratio due to gravity. The apices of the lungs have less particle filtration because of lower blood and lymphatic flow compared to the bases of the lungs.Panlobular
Panlobular emphysema, also called panacinar emphysema, affects all of the alveoli in a lobule, and can involve the whole lung or mainly the lower lobes. This type of emphysema is associated with alpha-1 antitrypsin deficiency, and Ritalin lung, and is not related to smoking.Complications
Likely complications of centrilobular and panlobular emphysema, some of which are life-threatening, include: respiratory failure, pneumonia, respiratory infections, pneumothorax, interstitial emphysema, pulmonary heart disease, and respiratory acidosis.Paraseptal
Paraseptal emphysema, also called distal acinar emphysema, relates to emphysematous change next to a pleural surface, or to a fissure. The cystic spaces known as blebs or bullae that form in paraseptal emphysema typically occur in just one layer beneath the pleura. This distinguishes it from the honeycombing of small cystic spaces seen in fibrosis that typically occurs in layers. This type of emphysema is not associated with airflow obstruction.Bullous
When the subpleural bullae are significant, the emphysema is called bullous emphysema. Bullae can become extensive and combine to form giant bullae. These can be large enough to take up a third of a hemithorax, compress the lung parenchyma, and cause displacement. The emphysema is now termed giant bullous emphysema, more commonly called vanishing lung syndrome due to the compressed parenchyma. A bleb or bulla may sometimes rupture and cause a pneumothorax.Paracicatricial
Paracicatricial emphysema, also known as irregular emphysema, is seen next to areas of fibrosis as large spaces. The scarring is most often a result of silicosis, granulomatous infection, tuberculosis, or pulmonary infarction. It can be difficult to differentiate from the honeycombing of pulmonary fibrosis.HIV associated
Classic lung diseases are a complication of HIV/AIDS with emphysema being a source of disease. HIV is cited as a risk factor for the development of emphysema and COPD regardless of smoking status. Around 20 percent of those with HIV have increased emphysematous changes. This has suggested that an underlying mechanism related to HIV is a contributory factor in the development of emphysema. HIV associated emphysema occurs over a much shorter time than that associated with smoking; an earlier presentation is also seen in emphysema caused by alpha-1 antitrypsin deficiency. Both of these conditions predominantly show damage in the lower lungs, which suggests a similarity between the two mechanisms.Alpha-1 related
Emphysema may develop in some people with alpha-1 antitrypsin deficiency, the only genotype of chronic obstructive pulmonary disease. This usually occurs a lot earlier than other types.Ritalin lung
The intravenous use of methylphenidate, commonly marketed as Ritalin and widely used as a stimulant drug in the treatment of attention deficit hyperactivity disorder, can lead to emphysematous changes known as Ritalin lung. The mechanism underlying this link is not clearly understood. Ritalin tablets are not intended to be injected. They contain talc as a filler, and it has been suggested that talc exposure causes granulomatosis leading to alveolar destruction. However, other intravenous drugs also contain talc, and no emphysematous change is associated with those. High resolution CT scanning shows the emphysema to be panlobular.CPFE
is a rare syndrome that shows upper-lobe emphysema, together with lower-lobe interstitial fibrosis. This is diagnosed by CT scan. This syndrome presents a marked susceptibility for the development of pulmonary hypertension.SRIF
is another type of fibrosis that occurs in emphysematous lungs and can be identified by pathologists. Unlike CPFE, this type of fibrosis is usually clinically occult. Occasionally, however, some patients with SRIF present with symptoms and radiologic findings of interstitial lung disease.Congenital lobar
Congenital lobar emphysema, also known as congenital lobar overinflation and infantile lobar emphysema, is a neonatal condition associated with enlarged air spaces in the lungs of newborn infants. It is diagnosed around the time of birth or in the first 6 months of life, occurring more often in boys than girls. CLE affects the upper lung lobes more than the lower lobes, and the left lung more often than the right lung. CLE is defined as the hyperinflation of one or more lobes of the lung due to the partial obstruction of the bronchus. This causes symptoms of pressure on the nearby organs. It is associated with several cardiac abnormalities such as patent ductus arteriosus, atrial septal defect, ventricular septal defect, and tetralogy of Fallot. Although CLE may be caused by the abnormal development of bronchi, or compression of airways by nearby tissues, no cause is identified in half of cases. CT scan of the lungs is useful in assessing the anatomy of the lung lobes and status of the neighbouring lobes on whether they are hypoplastic or not. Contrast-enhanced CT is useful in assessing vascular abnormalities and mediastinal masses.