Chronic obstructive pulmonary disease (COPD): introduction

The World Health Organization (WHO) defines chronic obstructive pulmonary disease (COPD) as: 'a lung disease characterised by chronic obstruction of lung airflow that interferes with normal breathing and is not fully reversible'. This is in contrast to the variable airways obstruction seen in asthma which can be reversed by drug treatment. The airflow obstruction in COPD is due to damage to the lung structure and destruction of lung tissue (emphysema). This is normally due to smoking, but recurrent infection also contributes to the process. Whilst preventable (COPD is mainly caused by smoking) and increasingly treatable, the airflow obstruction seen in COPD is usually progressive. More recently the systemic effects of more severe COPD have been recognised, including weight loss, nutritional disturbances and abnormal skeletal muscle function. COPD is also frequently associated with, and may contribute towards, numerous co-existing diseases such as heart disease, osteoporosis and diabetes, which influence morbidity and mortality.

Common symptoms of COPD include a chesty cough with phlegm that persists and does not go away, frequent chest infections, shortness of breath and persistent wheezing. The increased risk of chest infections may result in hospitalisation due to the severity of infection. Measurement of lung function using spirometry confirms the diagnosis and helps to classify the severity of the disease. Spirometry measures the amount (volume) and speed (flow) of air that can be inhaled and exhaled, and is also useful to monitor the progress of the disease and the response to treatment.

COPD is an important cause of morbidity and mortality in Scotland and worldwide. The Scottish Burden of Disease study estimated that COPD was the ninth most common cause of overall burden in Scotland in 2016 (Scottish Burden of Disease Study 2016). The Scottish Burden of Disease study has published a briefing paper on COPD estimates for Scotland. This estimate is in contrast to the Global Burden of Disease study, whose report on Scotland ranked COPD as the second highest cause of overall burden in 2017. 

It is widely accepted that estimates of COPD prevalence underestimate the true burden of the disease. A cross-sectional study in Northern Sweden (Lindberg 2006) found that only 20 - 30% of people fulfilling the criteria for COPD had been correctly diagnosed. Underdiagnosis is more likely in patients with mild disease than in those with severe disease (5% diagnosed versus 50% diagnosed respectively). These findings are consistent with other studies in the literature which highlight the extent of COPD underdiagnosis.