Non-Atopic Asthma: Definitions, Classifications, Risk Factors, Diet, Prevalence

Overview

Asthma is one of the most common conditions worldwide, affecting nearly 300 million people and causing an estimated 250,000 deaths annually. The condition can be divided into two main types: Atopic and non-atopic asthma. These are also referred to as extrinsic and intrinsic asthma, respectively.

Non-atopic (intrinsic) asthma is any type of asthmatic condition not caused by allergens. Contrastingly, atopic asthma (extrinsic) symptoms are usually introduced by some type of asthma trigger. These allergy triggers often include pollen, dust, pet hair, and other aeroallergens. Unlike atopic asthma, the causes of non-allergic or non-atopic asthma are relatively unknown. However, non-atopic asthma symptoms usually develop later in life, and tend to be more severe than the symptoms of atopic asthma. 

Introduction

All types of asthmas are induced by the inflammation of the airways, or breathing tubes of the respiratory system, causing them to narrow and ultimately inhibit lung function. Asthma symptoms include wheezing, coughing, breathlessness, and chest tightness. Occasionally, symptoms can develop into severe asthma, or asthma attacks, and requires immediate medical attention. Although symptoms are relatively consistent across the different forms of asthma, several types exist. The two primary definitions of the condition are atopic and non-atopic asthma. 

First, atopic asthma often comes in the form of childhood asthma and is triggered by allergies. In this case, asthmatic patients experience airway inflammation as a result of the release of histamines by mast cells, which are a type of immune cell in the body. Many times, severe atopic asthma is also accompanied by hay fever (allergic rhinitis) or eczema (atopic dermatitis) in children. Second, non-atopic asthma symptoms can be induced by many factors and its onset is not well understood. Adults experiencing non-atopic asthma may be triggered by exercise, weather conditions, stress, and infections. 

Definition

Asthma comprises a large spectrum of symptoms, severity, and causes. As a result, groups of demographic features, clinical symptoms, lung function, and inflammation can be used to determine and define an “asthma phenotype”. Several tests can determine a diagnosis of asthma across both extrinsic (allergic) and intrinsic (non-allergic) phenotypic forms. 

First, a Sputum Induced test collects mucus from the lining of airways. This sample will contain cells affected by the type of inflammation that causes asthmatic symptoms. If an asthma patient has an atopic condition or allergen-induced type, they are likely to have increased levels of immunoglobulin E (IgE) proteins in their samples. IgE binds to immune-response related cells, like mast cells, and triggers the inflammatory process associated with allergic asthma. However, if an asthma patient has high levels of eosinophils (a type of white blood cell that also causes high levels of inflammation in the lungs, sinuses, and airways), they are more likely to be diagnosed with non-atopic asthma. Eosinophilic asthma more often affects adult asthmatics and is also responsible for 50-60% of the most severe disease cases. Some forms of non-allergic asthma are not identifiable by the presence of either of these cells, however, and symptom causes are unclear. 

Symptoms

All symptoms of asthma, regardless of type, are dependent on the inflammation of airways resulting in constriction and narrowing. However, because the mechanisms that cause inflammation differ according to atopic and non-atopic asthma, asthma patients may experience a range of severity. 

The common symptoms of both atopic and non-atopic asthma are coughing, wheezing, shortness of breath, rapid breathing, and chest tightness. Although symptom type is similar between atopic and non-atopic asthma, their treatment options are very different. Often, the best way to treat severe allergic asthma is to avoid asthma triggers that will exacerbate inflammation. These triggers vary according to the individual allergic asthmatic, however, the most common allergens that can lead to symptoms are dust, pollen, pet hair, environmental pollutants, and mold. 

Because the development of severe allergic asthma is dependent on contact with a trigger, extrinsic asthma patients tend to have acute bouts of symptoms that can be treated with an emergency-use inhaled corticosteroid (or inhaler). Commonly, allergic asthma symptoms are accompanied by hay fever or eczema. Contrastingly, non-atopic asthma is not necessarily triggered by contact with a particular molecule, and instead, non-atopic asthma patients experience persistent and chronic asthma symptoms. That being said, severe non-atopic asthma attacks can also be triggered by vigorous exercise, anxiety, and respiratory infections. If symptoms are not addressed, they can eventually develop into chronic bronchitis, where the bronchi in the lung are persistently inflamed. Due to the variety and ambiguity of causes, treatment options for non-atopic asthmatics are limited. However, in the case of eosinophilic asthma patients, omalizumab, a type of injection that prevents the production of immune-response substances that can trigger inflammation, has been useful. Furthermore, some cases of intrinsic asthma are also manageable with the use of inhaled corticosteroids. 

Classifications

Confusingly, many names and types of asthma exist. Broadly, the condition as a whole is often referred to as bronchial asthma. Bronchial asthma encompasses all symptoms of inflammatory disease of the respiratory tract. Although the general condition varies in severity, the term bronchial hyperresponsiveness is commonly used to clinically describe an asthma attack, regardless of extrinsic/intrinsic status. The differences between atopic and non-atopic asthma have already been discussed, however, the types of symptoms experienced by all asthmatics can be divided into various categories. 

Some of the most common types are nocturnal asthma, occupational asthma, and cough variant asthma. These experiences can fall under either extrinsic or intrinsic diagnoses. 

• First, nocturnal asthma is typical of asthmatics whose symptoms are most persistent during the night. They may lose sleep due to breathing difficulties that limit the overall quality of life. This type of asthma problem is especially serious among non-allergic asthmatics who find that anxiety triggers their symptoms. Lack of sleep can exacerbate stress, creating a feedback loop where the symptoms cause sleep loss to become more severe. 
• Second, occupational asthma occurs when a workplace trigger causes asthma symptoms among employees. This trigger can be allergenic or otherwise, but often this type of condition is reversible when the workplace asthma triggers are avoided. 
• Next, cough variant asthma can afflict both atopic and non-atopic asthmatics, however, a dry cough is the only symptom of the condition that is experienced. The cough may become chronic, persisting for at least 6-8 weeks, and is usually exacerbated by exercise, stress, and respiratory tract infections. Interestingly, this asthma variant is most often experienced by patients using beta-blockers to treat high blood pressure, heart disease, or migraines. Understanding the side effects of any medication is the best proactive treatment for managing cough variant asthma symptoms.

There is also a fourth type of asthmatic condition completely unrelated to atopic and non-atopic forms. This condition is called exercise-induced asthma. Although an asthmatic’s symptoms can be triggered by exercise, this form only occurs in people without asthma, who get asthma-like symptoms from exercise. Also referred to as exercise-induced bronchoconstriction (EIB), the condition primarily influences pro-athletes practising in very cold environments. In the case of someone with a diagnosis of atopic or non-atopic asthma, the best way to reduce symptoms exacerbated by exercise is to use an inhaler. 

Risk Factors

The risk factors for developing either extrinsic or intrinsic asthma differ widely between patients and contexts. However, a few themes have been observed across the two types of asthma. First, family history plays an important role in the risk of developing both allergic and non-allergic asthma. In fact, children of parents with asthma are up to five times more likely to also suffer from asthmatic symptoms. This theme remains consistent across both atopic and non-atopic conditions and is likely connected to genetics and environmental contexts. Second, occupational exposures can also lead to either extrinsic or intrinsic asthma. These exposures may be allergenic, for instance workplace exposure to dust, mold, or other allergens, but they may also be non-allergenic. Examples of non-allergenic workplace exposures include high stress levels or manual labor that requires exercise. 

Although the two risk factors explored above can apply to both allergenic and non-allergenic asthmatics, there are some risk factors that apply only to atopic types. The first of these factors is allergies. Sufferers of atopic dermatitis (eczema) or allergic rhinitis (hay fever) are more likely to also struggle with severe allergic asthma. The second atopic asthma-specific risk factor is smoking or air pollution. Both of these forms of smoke-related aeroallergens trigger airway inflammation and can lead to extrinsic asthma symptoms. Furthermore, the risk of developing severe allergic asthma applies both to smokers and inhalers of second-hand smoke. 

Similarly, there are several risk factors that influence one’s risk of developing non-atopic asthma. The first of these factors is viral infection. The effects of viral infections, especially respiratory types, can trigger an inflammatory immune response that causes non-atopic asthma symptoms. This impact holds especially true in the case of infections that lead to chronic bronchitis, or prolonged inflammation of the bronchi. There’s evidence to suggest that children who suffer viral infections that cause bronchitis may later develop chronic asthma in adulthood. The second risk factor for developing intrinsic asthma, although the reason is unclear as to why, is obesity. It is hypothesized that obesity causes low-grade inflammation throughout the body that can become exacerbated by other non-atopic triggers such as exercise, stress, and infection. 

Diet

Unfortunately, there is no diet-related cure for asthma of any type. However, the following steps may help mitigate symptoms and improve general health. First, eating to reduce weight in the case of obesity may help to improve non-atopic asthmatic symptoms. Second, eating fruits and veggies full of antioxidants will likely reduce inflammation. Although these foods will not impact acute inflammation caused by allergic asthma triggers, they may reduce general inflammation associated with chronic asthma conditions or infection. Third, consuming vitamin D has been shown to improve asthma-associated issues. Vitamin D has been linked to a decreased incidence of asthma attacks and exacerbated symptoms. Furthermore, the supplement is also known to boost lung function and help the body fight off viral infections that might otherwise trigger breathing problems. Finally, reducing sulphite intake may also help improve asthma symptoms. Often found in wine, beer, shrimp, and dried fruits, sulphites cause wheezing and other asthma-like experiences in some people. Understanding your triggers and taking precautions is the best way to avoid asthma-inducing products. 

Treatment

Treatments for asthma vary widely according to type, severity, and triggers. However, several effective mitigation tools can be used to keep symptoms at bay. The most common form of asthma treatment is an inhaler. The inhaler comes in two forms: reliever and preventer inhalers. Reliever inhalers are normally blue in color and are implemented for the immediate relief of acute asthmatic symptoms. Therefore, they are a great option for allergic asthma that may have a quick onset of intense symptoms. The side effects of reliever inhalers include shakiness and raised heart rate for a few minutes after use. 

The second type of inhalers are preventer inhalers, which contain steroids and are designed for more frequent use. Preventer inhalers reduce the onset of inflammation, therefore stopping the development of symptoms. Your doctor will likely lay out a plan for how often to use your preventer inhaler, and it is important to continue its use even if you are not experiencing symptoms. Some side effects of preventer inhalers include oral thrush, hoarse voice, and a sore throat. 

Various medications for asthma are also available. Tablets are commonly used when inhalers are not effective and include leukotriene receptor antagonists (LTRAs), theophylline, and other steroids. Implementation of these treatments prevents the onset of inflammation at the cellular level. Some of their side effects include weight gain, mood changes, bone fragility, and high blood pressure. 

Finally, if the above treatments prove ineffective against particularly chronic forms of asthma, injections every few weeks may be recommended. Injections are not right for every asthmatic and can only be prescribed by a specialist. Their forms include omalizumab, benralizumab, and others.