Asthma is sometimes classified in various ways. Often, these “types of asthma” describe the triggers that may cause an asthma episode (or asthma attack) or the things that make asthma worse in certain individuals. There are various different types of asthma, some of which are difficult to readily diagnose. Further complicating accurate diagnosis is that, at times, and in certain individuals, there are very specific symptoms (or patterns of symptoms) unique to any one person.
When asthma does begin in childhood, it often does so in a child who is likely, for genetic reasons, to become sensitized to common “allergens” in the environment (atopic person). When these children are exposed to house-dust mites, animal proteins, fungi, or other potential allergens, they produce a type of antibody that is intended to engulf and destroy the foreign materials. This has the effect of making the airway cells sensitive to particular materials. Further exposure can lead rapidly to an asthmatic response. This condition of atopy is present in at least one-third and as many as half of the general population. When an infant or young child wheezes during viral infections, the presence of allergy (in the child itself or a close relative) is a clue that asthma may well continue throughout childhood.
Adult-onset asthma develops after age 20. It is less common than asthma in children, and it affects more women than men. Allergenic materials may also play a role when adults become asthmatic. Asthma can actually start at any age and in a wide variety of situations. Although less common than asthma in children, adult-onset asthma can also be triggered by allergies.
Between 30 percent and 50 percent of all adult cases are associated with allergies, but often allergic exposures don’t seem to be the most important, driving factors. This nonallergic adult-onset asthma is sometimes called “intrinsic.” Many adults who are not allergic do have such conditions as sinusitis or nasal polyps, or they may be sensitive to aspirin and related drugs. Another major source of adult asthma is exposure at work to animal products, certain forms of plastic, wood dust, or metals.
Shortness of breath and/or wheezing occurring after strenuous exercise is called exercise-induced asthma. Although this phenomenon happens in up to 80% of people with recognized asthma, it frequently takes place as an isolated event without any other symptoms of asthma at any other time. This complicates any diagnosis of asthma as an underlying cause because frequently this form of asthma is confused with poor physical conditioning or possible heart problems. Nevertheless, asthma should always be suspected as a possible cause of exercise-induced wheezing or shortness of breath, especially when the person is otherwise healthy.
Exercise-induced asthma involves symptoms that occur about 5-20 minutes after beginning an exercise that involves breathing through the mouth. Sports and games that require continuous activity or that are played in cold weather (for example, long-distance running, hockey, soccer, and cross-country skiing) are the most likely to trigger an asthma attack. Other physical exertions that can trigger an attack include laughing, crying, and hyperventilating.
Coughing can occur alone, without the other symptoms of asthma that are usually present and recognized by the physician or patient. Cough variant asthma causes great difficulty for the physician to accurately diagnose the true underlying cause of the cough as being asthma because it can be easily confused with other conditions, such as chronic bronchitis and post nasal drip due to hay fever or sinus disease. Coughing can occur day or night. Nighttime coughing is most disruptive, interfering with sleep.
Occupational asthma occurs in response to a trigger in the workplace. Triggers include contaminants in the air, such as smoke, chemicals, vapors (gases), fumes, dust, or other particles; respiratory infections, such as colds and flu (viruses); allergens in the air, such as molds, animal dander, and pollen; extremes of temperature or humidity; and emotional excitement or stress. In occupational asthma, the trigger is a substance or condition in the workplace that causes asthma symptoms. Most of these substances and conditions are very common and are not normally considered hazardous. Although these substances and conditions can be encountered in almost any workplace, occupational asthma is most common in workers in the following industries and jobs. In most people with occupational asthma, the symptoms appear a short time after beginning work and subside after leaving work.
Nocturnal asthma occurs between midnight and 8 am. It is triggered by allergens in the home such as dust and pet dander or is caused by sinus conditions. Nocturnal or nighttime asthma may occur without any daytime symptoms recognized by the patient. This is called “nocturnal asthma.” The patient may have wheezing or short breath when lying down or may not notice these symptoms until awoken by them in the middle of the night, usually between 2 and 4am. Nocturnal asthma may occur only once in a while or frequently during the week.
Nighttime symptoms may also be a common problem in people who have daytime asthma as well, but then its true nature is more readily recognized. When there are no daytime symptoms to suggest asthma is an underlying cause of the nighttime cough, this type of asthma will be more difficult to recognize and usually delay proper therapy. The cause (or causes) of this phenomenon is unknown, although many possibilities are under investigation.
Steroid-resistant asthma (severe Asthma): While the majority of patients respond to regular inhaled glucocorticoid (steroid) therapy, some are steroid resistant. Airway inflammation and immune activation plays an important role in chronic asthma. Current guidelines of asthma therapy have therefore focused on the use of anti-inflammatory therapy, particularly inhaled glucocorticoids (GCs). One of the major mechanisms by which glucocorticoids act in asthma is by reducing airway inflammation and immune activation.
However, patients with steroid resistant asthma have higher levels of immune activation in their airways than do patients with steroid sensitive (SS) asthma. Furthermore, glucocorticoids do not reduce the eosinophilia or T cell activation found in steroid resistant asthmatics. This persistent immune activation is associated with high levels of IL-2, IL-4 and IL-5 in the airways of these patients.