The most important symptoms of COPD are breathlessness on exertion and chronic cough with or without phlegm. The dyspnoea usually worsens over time but is often not present in mild or moderate COPD. The cough may be dry or productive. Cough and phlegm often precede dyspnoea on exertion by many years. Other symptoms include wheezing and chest tightness. As the disease progresses and reaches the severe stages, fatigue, weight loss and anorexia may increase. To establish the diagnosis of COPD, lung function measurement by spirometry is necessary.
A characteristic of COPD is exacerbations or episodes of acute worsening of the respiratory symptoms. The most common causes of exacerbations are viral or bacterial infections. Increased air pollution also appears to precipitate exacerbations of COPD. Some patients are particularly prone to exacerbations while others are not. Two or more exacerbations during the previous year is the most important indicator of a future exacerbation.
Exacerbations accelerate the decline in lung function that characterises COPD, resulting in reduced physical activity, poorer quality of life, and an increased risk of death; they are also responsible for a large proportion of the healthcare costs attributable to COPD.
Patients with COPD often suffer from other diseases (comorbidities). The comorbidities may share common risk factors with COPD, in particular cigarette smoking. They may also represent extrapulmonary manifestations or complications of COPD, such as muscle dysfunction due to inactivity. Comorbidities may be secondary to treatment of COPD; for example, osteoporosis due to oral corticosteroid treatment. The most common comorbidities in COPD are ischaemic heart disease, anxiety and depression, osteoporosis, skeletal muscle dysfunction, gastro-oesophageal reflux, anaemia, lung cancer, diabetes and metabolic syndrome. Comorbidities contribute to the overall severity and manifestations of the disease. They can occur in mild, moderate or severe COPD and they increase the risks of hospitalisation and mortality of COPD independently.
The clinical effects of COPD show considerable inter-individual variation, depending on which respiratory symptoms predominate, the frequency of exacerbations, the level and rate of lung function decline and the amount of emphysema, as well as comorbidities. Various subtypes of the disease are often termed phenotypes of COPD.