Emphysema is irreversible enlargement of the airspaces with destruction their walls without obvious fibrosis. Emphysema is one of the diseases known collectively as chronic obstructive pulmonary disaese (COPD).
Emphysema has four types based on anatomic distribution in the lobule.
Centriacinar emphysema is the most common form, more than 95% of clinical cases.
Centriacinar (Centrilobular) Emphysema
In this type of emphysema the central or proximal parts of acini are affected while distal alveoli are spared. Both affected and non-affected are in the same region. The lesions are more common and more severe in the upper lobes, especially in the apical segments. Inflammation is common around brochi and bronchioles. If the centriacinar emphysema is very heavy, the distal parts of acini may be involved, making differentiation from panacinar emphysema difficult. Centriacinar emphysema occurs predominantly in heavy smokers, often in association with chronic bronchitis (COPD).
Panacinar (Panlobular) Emphysema
In this type, the acini are uniformly enlarged from the level of the respiratory bronchiole to the terminal blind alveoli. The prefix “pan” refers to the entire acinus, not the entire lung. In contrast to centriacinar emphysema, panacinar emphysema tends to occur more commonly in the lower zones and in the anterior margins of the lung, and it is usually most severe at the bases. This type of emphysema is associated with α1-antitrypsin deficiency.
A, Centriacinar emphysema. Central areas show marked emphysematous damage (E), surrounded by relatively spared alveolar spaces. B, Panacinar emphysema involving the entire pulmonary lobule.
Distal Acinar (Paraseptal) Emphysema
Proximal parts is normal while distal part is predominantly affected. It is usually more severe in the upper half of the lungs. The characteristic findings are of multiple, continous, enlarges airspaces 0.5 – 2.0 cm in diameter sometimes forming cystlike structures. This type of emphysema probably underlyes many cases of spontaneous pneumotorax in young adults.
Airspace Enlargement With Fibrosis (Irregular Emphysema)
Acinus involves irregularly, so named irregular emphysema. It is almost always associated with scarring. In most cases it is not significant clinically.
Inhaled cigarette smoke and other noxious particles cause lung damage and inflammation, which results in parenchymal destruction (emphysema) and airway disease (bronchiolitis and chronic bronchitis).
Inflammatory mediators and leukocytes: Many mediators are increased in the affected area, released by resident epithelial cells and machrophages.
Symptoms do not appear until at least one third of the functioning pulmonary parenchyma is damaged. Dyspnea usually appears first, beginning insidiously but progressing steadily. In some patients, cough or wheezing is the chief complaint, easily confused with asthma. Cough and expectoration are extremely variable and depend on the extent of the associated bronchitis.
Weight loss is common and can be so severe as to suggest an occult cancer. Classically, the patient with severe emphysema is barrel-chested and dyspneic, with obviously prolonged expiration, sits forward in a hunched over position, and breathes through pursed lips. Impaired expiratory airflow, best measured through spirometry, is the key to diagnosis. In individuals with severe emphysema, cough is often slight, overdistention is severe, diffusion capacity is low, and blood gas values are relatively normal at rest. Such patients may overventilate and remain well oxygenated, and therefore are somewhat ingloriously designated pink puffers. Development of cor pulmonale and eventually congestive heart failure, related to secondary pulmonary hypertension, is associated with a poor prognosis. Death in most patients with emphysema is due to (1) coronary artery disease, (2) respiratory failure, (3) rightsided heart failure, or (4) massive collapse of the lungs secondary to pneumothorax. Treatment options include smoking cessation, oxygen therapy, long-acting bronchodilators with inhaled corticosteroids, physical therapy, bullectomy, and, in selected patients, lung volume reduction surgery and lung transplantation. α1-AT replacement therapy is being evaluated.
– To be continued…