What Is Cough-Variant Asthma?

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Cough-variant asthma is a form of asthma in which the primary symptom is a dry, non-productive cough. This differs from other forms of asthma in which coughing produces mucus. However, cough-variant asthma—especially when not properly treated—is often a precursor to "classic" asthma in which shortness of breath, wheezing, and chest pain are accompanied by a wet, productive cough.

Cough-variant asthma can be difficult to diagnose as chronic dry coughing can be attributed to many conditions.

Cough-Variant Asthma Symptoms

Cough-variant asthma is a confusing condition because it doesn't "read" as asthma to most people. A chronic, non-productive cough is the distinguishing feature, but there are no other typical signs or symptoms of asthma.

There are many reasons why a person might develop a chronic cough (defined as a cough lasting more than eight weeks in adults and four weeks in children). The first clue that asthma is involved is the timing of the severe coughing episodes.

Cough-variant asthma should be suspected if:

Cause

As with classic asthma, no one really knows what causes cough-variant asthma. In some cases, cough-variant asthma may be an early sign of the onset of classic asthma. Children are more affected by cough-variant asthma than adults, and this adds credence to the hypothesis.

There is growing evidence that asthma is part of a continuum of disorders called the atopic march. Atopy, a genetic tendency toward allergic diseases, is believed to develop from early childhood when an immature immune system is exposed to substances that it does not yet recognize as harmless.

The immune overreaction can set off a chain reaction in which the immune system progressively regards other substances as harmful.

The atopic march classically starts with atopic dermatitis (eczema), which can progress to food allergies and finally to allergic rhinitis (hay fever) and asthma. It is possible that cough-variant asthma is simply a transitional step in the march.

With that said, not everyone who has cough-variant asthma will develop classic asthma. A 2010 review of studies from Italy suggests that only around 30% of people with cough-variant asthma will go on to do so.

Given it is a milder form of the disease, cough-variant asthma is far more likely to resolve on its own by the teen or adult years than moderate persistent or severe persistent asthma.

Prospective studies have also suggested that one of four people with idiopathic chronic cough (cough of unknown origin) have cough-variant asthma.

Diagnosis

Cough-variant asthma can be easily misdiagnosed and difficult to confirm even if the disease is suspected.

Asthma is mainly diagnosed based on your symptoms, medical history, and a variety of tests that evaluate your lung function. These tests, called pulmonary function tests (PFTs), measure the capacity of the lungs and the force of exhalations after exposure to different substances. Other tests may be considered, as needed.

Pulmonary Function Tests

For adults and children over 5, the first PFT used is called spirometry. It involves a device called a spirometer into which you breathe so that your forced expiratory volume in one second (FEV1) and forced volume capacity (FVC) can be measured. These initial FEV1 and FVC values are then retested after you have inhaled a medication called a bronchodilator that opens the airways.

Based on changes in the FEV1 and FVC values, the doctor may have sufficient evidence to definitively diagnose asthma. But a downside of spirometry—beyond the fact that is cannot be used in younger children whose lungs are still developing—is that is it has a high rate of false-positives results. This makes borderline results much harder to interpret.

If spirometry tests are anything less than certain, another test called a bronchoprovocation challenge may be conducted. For this test, the FEV1 and FVC values are compared before and after exposure to substances or events that can trigger allergy symptoms. These include:

  • Methacholine, an inhaled drug that can cause bronchoconstriction (narrowing of the airways) in people with asthma
  • Exercise, which may trigger exercise-induced allergy
  • Cold air, which may trigger cold-weather asthma
  • Histamine, a naturally occurring substance that may trigger allergic asthma

The problem with bronchoprovocation is that people with cough-variant asthma have less hyperresponsiveness (airway sensitivity) than people with classic asthma and tend to be less responsive to methacholine and other stimuli.

Sputum Culture

If in doubt, a doctor may ask for a sputum sample so that it can be sent to a lab for evaluation. People with asthma often high levels of white blood cells can eosinophils. High eosinophil values may help support the diagnosis of cough-variant asthma. (With that said, people with cough-variant asthma tend to have lower eosinophil counts compared to those with classic asthma.)

Breath Test

Similarly, a breath test for exhaled nitric oxide (an inflammatory gas released from the lungs) is highly predictive of cough-variant asthma even if all other tests are inconclusive.

Even if tests are not strongly conclusive, some doctors will presumptively treat cough-variant asthma with a short-acting rescue inhaler like albuterol if the symptoms are strongly suggestive of the disease. If the symptoms resolve or improve under treatment, it can help support the provisional diagnosis.

Differential Diagnoses

If test results are uncertain but symptoms persist, the doctor may expand the investigation to explore other possible causes of chronic cough in the differential diagnosis. This may include:

Treatment

The treatment of cough-variant asthma is virtually the same as for classic asthma. If the symptoms are mild and intermittent, an albuterol inhaler may be all that is needed. If the symptoms are persistent, an inhaled corticosteroid like Flovent (fluticasone) may be used on a daily basis to reduce airway inflammation hyperresponsiveness.

Some doctors endorse a more aggressive approach to treatment under the presumption that it may prevent the onset of classic asthma. This is especially true if coughing fits are severe.

In cases like these, the doctor may prescribe a rescue inhaler, a daily inhaled corticosteroid, and a daily oral drug known as a leukotriene modifier until the chronic cough resolves. If needed, an oral corticosteroid may be added for one to three weeks if the coughing episodes are severe.

Once the symptoms are fully resolved, daily inhaled corticosteroids may be continued to prevent them from returning. A doctor can then monitor your condition and determine how long daily treatment is needed.

A Word From Verywell

Any cough that lasts more than eight weeks in adults or four weeks in children should not be ignored as this may be an early sign of asthma. Speak with your doctor and keep a diary detailing when coughing episodes occur (such as at nighttime or after exercising). By reviewing these insights, a doctor may be able to pinpoint asthma as the cause and start treatment.

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