Asthma COPD overlap syndrome (ACOS) is an umbrella term that doctors use when a person has both asthma and chronic obstructive pulmonary disease (COPD). These lung diseases share some similarities, but they are separate conditions.

ACOS is a recent term, and research into the causes and treatment is in its early stages. Recognizing ACOS as the co-occurrence of two separate diseases helps doctors tailor the treatment to make it specific to a person’s symptoms.

This article examines the symptoms, causes, and treatment of ACOS and explains how doctors diagnose it.

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Doctors diagnose ACOS when a person has symptoms of asthma and COPD. Both of these conditions make breathing difficult. However, as the American Lung Association (ALA) notes, they are two different lung diseases.

ACOS is not a separate condition but an umbrella term that doctors use when both asthma and COPD are present. COPD itself is also an umbrella term for two chronic lung conditions: emphysema and chronic bronchitis.

The ALA identifies the following as symptoms of ACOS:

  • problems with breathing
  • excessive amounts of mucus
  • fatigue
  • frequent coughing
  • frequent shortness of breath
  • wheezing

The American College of Asthma, Allergy, & Immunology also cites a feeling of tightness in the chest and a low tolerance for physical activities, such as exercise.

A small 2018 study involving 30 people, 20 of whom had ACOS, found that shortness of breath was the most frequent symptom and the one that caused the most discomfort. It also found that people with ACOS were more likely to experience an exacerbation of symptoms than those with COPD but not asthma. These attacks can involve coughing more than usual, being sick, or being unable to breathe.

A 2022 study also found that in comparison with people with COPD or asthma, those with ACOS are more likely to have:

  • a lower quality of life
  • more severe symptoms
  • more frequent flare-ups

Clinical definitions of ACOS vary, but doctors usually refer to the following criteria:

  • persistent airflow obstruction, which may or may not be reversible
  • history or symptoms of asthma
  • history of smoking
  • two positive responses to bronchodilator reversibility tests
  • history of rhinitis or allergies

Doctors will begin testing with a pulmonary function test, known as spirometry. They may then use bronchodilator reversibility tests, in which they will give a person a bronchodilator to inhale and then measure how significantly this improves their breathing. A 2022 study looked at the effectiveness of bronchodilator testing when doctors performed it without spirometry. The results showed that it could increase the risk of ACOS misdiagnosis by up to almost 20%.

A doctor will also take a detailed medical history and perform a physical examination. They may sometimes order imaging tests, such as an X-ray, CT scan, or MRI scan, to look at the lungs.

As a 2021 study points out, the criteria for what defines ACOS are still under debate, and researchers continue to work on new methods of testing and diagnosis.

The uncertainty around diagnosis means that it is difficult to be sure of the prevalence of ACOS. Studies show significant variations, with estimates ranging from just under 1 in 100 people to more than 1 in 10 people. However, a large-scale 2019 analysis of data for the Clinical Respiratory Journal states that it affects about 1% of the population in the United States.

As ACOS refers to the presence of both asthma and COPD, it is necessary to look at the causes and triggers of each of these in turn.

Asthma causes and triggers

Respiratory experts do not know exactly what causes asthma. However, there are some known risk factors, including:

  • a family history of asthma or allergies
  • smoking tobacco
  • being exposed to smoke when in the womb
  • obesity
  • living in an area with poor air quality

Common triggers that cause asthma flare-ups include dust mites, smoke, mold spores, pet dander, poor air quality, and strong smells. Stressful situations, viral and bacterial infections, weather changes, and physical exercise can also produce or worsen symptoms.

COPD causes and triggers

The World Health Organization (WHO) notes that COPD develops gradually over years, with the following factors increasing a person’s risk of developing the disease:

  • exposure to tobacco smoke, harmful chemicals or fumes, or indoor air pollution
  • impaired growth in the womb or premature birth
  • frequent respiratory infections or asthma in childhood
  • a rare genetic condition called alpha-1 antitrypsin deficiency

The primary triggers of COPD are viral and bacterial infections. Some people with COPD are more susceptible to these infections than others and are, as a result, likely to experience more frequent flare-ups.

ACOS causes and triggers

More recent studies have aimed to look at the potential causes of ACOS. A 2021 study has cited emerging evidence that certain risk factors may cause people with pre-existing respiratory problems to develop ACOS. These risk factors include childhood respiratory illness, smoking, and environmental factors, such as exposure to harmful fumes.

As the ALA points out, treatment for ACOS is not straightforward, and no single medication can improve the symptoms of ACOS. However, certain drugs can help improve the symptoms. These include:

  • Long-acting muscarinic receptor agonists: Doctors recommend these drugs for people with COPD, as they help stop the airways from tightening and producing excess mucus or phlegm. Studies have shown that they are effective in both asthma and COPD. Experts recommend using them as a first-line treatment for ACOS, with inhaled steroids as an add-on treatment.
  • Low dose inhaled corticosteroids: These drugs treat inflammation in the airways. A 2022 study showed that although people with ACOS experienced more severe symptoms than people with asthma or COPD alone, they had a better response to inhaled corticosteroid treatment.
  • Long-acting bronchodilators: These asthma medications keep the airways open for longer. Doctors will combine the medication with anti-inflammatory drugs.
  • Biologics: Researchers are still investigating the potential role of biologics in ACOS treatment, but doctors may add this therapy to a person’s treatment regimen if their current medications are proving ineffective.

More recently, studies have shown that a drug called roflumilast, which has anti-inflammatory properties, is effective in treating people with asthma, COPD, or ACOS.

A doctor will also recommend making certain lifestyle adjustments. These include:

  • stopping smoking, if applicable
  • getting vaccinations against respiratory illnesses such as influenza and pneumonia
  • engaging in regular physical activity to improve overall health

In some cases, it may be necessary to refer a person with ACOS to a specialist.

ACOS is a chronic disease, which means that there is no cure. People with ACOS tend to have a higher disease burden than people with asthma or COPD. This means that they are more vulnerable to infections and more likely to see their symptoms worsen over time. They are also more likely to have a lower quality of life.

However, it is important to remember that the identification and treatment of ACOS are in their infancy. Clinicians and scientists are conducting new research and clinical trials to improve outcomes for people with ACOS.

Asthma COPD overlap syndrome is a term that doctors use when a person has both asthma and chronic obstructive pulmonary disease.

The symptoms include shortness of breath, fatigue, and wheezing. Experts are still working to discover the causes, but they believe that childhood respiratory illnesses and smoking play a role.

Doctors will create a tailored treatment plan for a person with ACOS, but they will typically recommend treatments for asthma and COPD.