An Overview of Reactive Airway Disease

Reactive airway disease (RAD) is a general term used to describe a reaction in which the bronchial tubes of the lungs overreact to an irritant, triggering wheezing and shortness of breath. While it's easy to assume that RAD is the same thing as asthma, RAD is actually no more than a placeholder for almost any restrictive respiratory event that has not been officially diagnosed. In other words, it's simply a classification of symptoms related to any number of conditions, including asthma, chronic obstructive pulmonary disease (COPD), and certain bronchial infections.

The term RAD is most commonly applied in pediatrics when a child experiences asthma-like symptoms but is too young to undergo a bronchial challenge test or other forms of diagnostic evaluation.

While the term RAD is not meant to confuse people, it frequently does. The confusion stems in part from the different term "reactive airway dysfunction syndrome (RADS)," which was coined in 1985 by American pulmonologist Stuart Brooks to describe a single toxic inhalation of smoke, fumes, or corrosive gases that leads to a long-term, often chronic lung condition mimicking a severe form of COPD.

Since that time, the shortened "reactive airway disease (RAD)" has been increasingly used to describe a wide range of diseases that cause asthma-like symptoms. The problem is that it is not a medical term, per se, and has different definitions depending on who you speak to. Some doctors will use RAD to describe diseases that cause reversible airway narrowing, while others will include COPD, which is clearly not reversible. To add even more confusion, some—including medical professionals—will misuse RAD as a synonym for asthma.

For their part, the American Academy of Allergy, Asthma, and Immunology (AAAAI) has labeled the term "imprecise" and "lazy," believing that it suggests a diagnosis in the absence of an actual investigation.

Others contend that the term has an appropriate usage, particularly in pediatrics or emergency care. Moreover, the very non-specificity of the classification, some argue, is meant to incite clinicians to look beyond the obvious causes and explore less common (and potentially more serious) explanations for symptoms.

You could be said to have RAD if you are experiencing wheezing, shortness of breath, and a persistent, productive cough. This cluster of symptom is triggered by a common physiological response, whether you have asthma, COPD, or other reactive respiratory conditions:

• Breathing limitation is caused when the smooth muscles of the lungs are hyperresponsive, cause airways to contract and narrow.
• Inflammation is caused by the body's response to allergens in the lungs. This causes swelling and further narrowing of air passages.
• Excessive mucus is produced in response to both of the conditions, clogging the airways and tiny air sacs of the lungs (called alveoli).

Depending on the severity of the response, symptoms can range from mild to life-threatening.

Again, RAD is not a diagnosis, but rather a characterization of physical symptoms. It serves only as the launching point for an investigation, the direction of which can vary based on your age, medical history, symptoms, and events leading up to the attack.

The shortlist of common and uncommon causes include:

• Allergic bronchopulmonary aspergillosis, or ABPA, is a fungal infection in which asthma-like symptoms are often accompanied by the coughing up of blood. It is not an infection per se, but a colonization and resultant allergic and immune reaction within the lung. 
• Asthma, which can occur at any age and often runs in families
• Bronchiectasis, a chronic lung condition differentiated by audible crackles when breathing and finger clubbing
• Bronchiolitis obliterans, a severe lung disease often affecting younger people who do not smoke
• Congestive heart failure, often accompanied by leg swelling, chest pains, and irregular heartbeat
• COPD, typically associated with long-term exposure to cigarettes or toxic fumes
• Cystic fibrosis, a congenital disease affecting children at a young age and characteristically accompanied by chronic digestive problems
• Gastroesophageal reflux disease, or GERD, in which asthma-like symptoms are accompanied by chronic acid reflux
• Granutalomous lung disease, granular formations in the lungs caused by fungal or mycobacterial infections or by immune-mediated disorders like sarcoidosis or granulomatosis with polyangiitis
• Occupational asthma, commonly affecting bakers, farmers, grain elevator operators, metal workers, plastic workers, and woodworkers
• Hypersensitivity pneumonitis, an immune condition that in the acute phase (short term) mimics asthma, and in the chronic phase (long term) can mimic COPD 
• Pulmonary embolus, a blood clot in the lungs often occurring in people with heart disease, cancer, or who have had recent surgery
• Upper respiratory viral infection, in which asthma-like symptoms are accompanied by high fever, chills, and body aches

The approach to diagnosis is as varied as the possible causes. By and large, doctors will pursue investigations based on the diagnostic clues noted in the initial exam.

These may include:

• Bronchoprovocation challenge testing and peak expiratory flow rate (PEFR) to help diagnose asthma
• Pulmonary function tests like spirometry, diffusion studies, and body plethysmography to diagnose COPD
• Imaging tests like chest X-rays, computed tomography (CT), and magnetic resonance imaging (MRI) to investigate heart disease, lung disease, or cancer
• Blood tests or cultures to detect inflammation or infection
• Skin prick and RAST blood tests to identify allergy triggers
• Lung biopsy to help evaluate suspicious tissue growths
• Antinuclear antibody (ANA) blood tests to help diagnose autoimmune disease
• CF gene mutation panel to diagnose cystic fibrosis
• Bronchoscopy, in which a viewing scope is inserted into the windpipe to determine whether acid reflux is a cause

In pediatric cases, RAD may be notated in the infant's medical records if no apparent cause is found in the early investigation. The aim of the notation is to ensure that the baby's condition is monitored until such time as more definitive diagnostic tools can be used.

There are no clear treatment guidelines for reactive airway disease. In emergency situations, the classification would help direct rescue efforts, which may include:

• Emergency oxygen therapy
• Pulse oximetry to assess oxygen blood saturation
• Inhaled rescue bronchodilators (or intravenous bronchodilators in severe cases)
• Epinephrine injections if symptoms are suggestive of potentially life-threatening allergic anaphylaxis

In such situations, the term RAD provides emergency room staff with a shorthand of symptoms once the patient is delivered by ambulance personnel.