I almost never prescribe cough medicine for a cough. That's the equivalent of saying: "I don't care why you're coughing — let's just try to cover it up." A cough is a protective reflex. It is the body's way of responding to irritation. So when a cough persists, I don't want to simply silence it without understanding why it is occurring.
The important questions are:
- What is irritating the airway?
- Are there multiple triggers?
- Is coughing itself perpetuating another trigger (like reflux)?
- What can we do to break the cycle?
Most physicians are familiar with a cough occurring in conjunction with asthma. However, if wheezing is not heard on physical examination, the physician may erroneously exclude the diagnosis of asthma. It is frequently underappreciated that mild asthma may not cause wheezing — the associated lung inflammation can still cause a cough. This is called cough-variant asthma. The upper airways (nasal passages, mouth, and throat) are neurologically connected to the lower airways (lungs). Inflammation in one part of this interconnected system can trigger an adverse response in another part of the system.
How Is Cough-Variant Asthma Confirmed?
Lung airways are surrounded by circular muscles. When airways are inflamed or neurologically over-stimulated, the muscles can contract and this narrows the airways. When air moves through smaller airways, a wheezing sound can occur. Reduced airflow through the airways also sends a signal to the brain that something is obstructing them — and the body's response is to try to clear the obstruction with a cough.
Clinically, asthma is typically diagnosed by observing a favorable response to bronchodilator medications (albuterol, formoterol, etc.). Within a few minutes after albuterol is administered, the circular muscles that surround the airways relax, resulting in larger airways and greater airflow. When airways relax to their normal size, wheezing often disappears and reflex coughing also commonly improves.
If asthma is the only cause of a cough, bronchodilators will typically produce a dramatic improvement. However, if other factors are also contributing to the cough, only a minimal reduction may be seen — and albuterol may be incorrectly judged to be ineffective. This can make it easy to overlook cough-variant asthma when evaluating a patient whose primary or only symptom is a persistent cough.
With the use of a Pulmonary Function Testing (PFT) device, if objective measurements demonstrate an improvement of greater than 15% in airflow following albuterol use, the diagnosis of asthma or cough-variant asthma can be confirmed.
Asthma Can Be Part of a Multifactorial Cough
A cough that begins after a respiratory viral infection or an allergen exposure does not necessarily have only one cause. Sinus infections commonly follow viral infections and also occur frequently during allergen seasons. Due to the airway's interconnections, sinus infections are a very common trigger for asthma. Therefore, even after the initiating trigger for a cough resolves, sinusitis, asthma, and even acid reflux may continue to perpetuate the cough.
The Cough Reflex Can Become Hypersensitive
Your cough reflex protects your airways from the aspiration of foreign matter. It keeps infected mucus from sinus infections out of your lungs. If food or liquid goes down the wrong way, coughing automatically keeps it from going deep into the lungs. A cough is a good thing when it is protecting you — but it becomes a problem when it is working overtime.
A cough that continues for a long period can make the cough reflex increasingly sensitive to minor irritants. Once the neurologic pathways involved in coughing become hypersensitive, stimuli that previously would have been insignificant may trigger a substantial coughing response.
A patient may begin coughing when:
- Talking or laughing
- Eating
- Smelling perfume
- Breathing cold air
- Lying down
- Swallowing
- Experiencing a small amount of drainage
- Experiencing a small amount of reflux
At this point, the coughing patient may have moved well beyond a simple "one trigger, one cough" situation. Once the nervous system itself has become part of the problem, eliminating all significant sources of irritation becomes even more important.
The Problem With Chasing Only One Trigger
The most common reason physicians struggle to stop a chronic cough is rooted in how they were trained. Many assume that because a cough often begins after a single identifiable trigger, there is one main cause perpetuating it. The strategy that follows is to hunt the "main" cause by treating the possible causes sequentially — trying one intervention, and if it fails, discontinuing it to try another.
But a cough may have several simultaneous drivers and no single "main" cause. Cough-variant asthma may be only one of them.
When three triggers are present, three treatments are required — but the only effective strategy is to treat all of the suspected triggers at the same time.
The Bottom Line
Cough-variant asthma can cause a cough without wheezing. When a patient also has post-nasal drainage, allergic inflammation, sinus disease, or reflux, there may be several simultaneous drivers keeping the cough alive.
That is why the approach to chronic cough should not simply be to search for the "main" cause. Instead, ask: "What are all of the factors contributing to this cough?" When multiple triggers are present, multiple treatments may need to be implemented at the same time. A cough with three significant triggers cannot reasonably be expected to disappear when only one or two triggers are being treated.
This article is intended for general educational purposes and does not replace an individualized medical evaluation. If you have a persistent cough, consult your healthcare provider for a thorough assessment.