When a cough just won't go away

Who has never had a cough? I bet no one can raise their hand. We see this in clinic all the time. But chronic cough— one that lasts at least eight weeks — can be hard for patients to deal with and difficult for doctors to figure out.

In the October 20, 2016 issue of the New England Journal of Medicine, lung experts describe a step-by-step approach doctors can use to help treat patients with chronic cough. Most often a prolonged cough is due to one of the "usual suspects." But when it's not, we have a long list of increasingly rarer conditions that we should run through and rule out. If it isn't due to any of those, experts now recognize that the culprit may be overactive nerves that cause an exaggerated cough response to certain triggers.

The "usual suspects" that may be behind a chronic cough

The authors describe a typical patient with chronic cough, and she is very similar to many of my patients. She's a middle-aged lady with a cough lasting many months. Of course, first we want to ask a whole lot of questions.

• Has she had chronic allergy symptoms such as itchy, watery eyes and nose, stuffy nose, and postnasal drip? If so, it's worth trying antihistamines and nasal steroids. Undertreated allergies can lead to chronic sinus infection, which causes cough by postnasal drip, so we may want to treat for this as well.
• Could she have "cough variant" asthma that causes a cough but no wheezing? Many of my patients would rather not wait for an appointment with a lung specialist and undergo fancy tests. So, if we suspect cough-variant asthma, we simply begin inhalers. A few weeks of inhaled albuterol to help open the airways and a steroid inhaler to quell inflammation may both make the diagnosis and treat the problem.
• Is she suffering from heartburn symptoms? Acid reflux can also trigger cough, and if someone describes heartburn symptoms, or even if we are not sure what is causing the cough, we often prescribe eight weeks of an acid-lowering medication.
• Is she taking a medication for which coughing is a side effect? Lisinopril or another blood pressure medication from the class called ACE inhibitors can cause cough in 20% of patients. A trial period off this medication may be warranted.
• Is she among the 17% of Americans who smoke cigarettes? If so, her cough may be due to chronic bronchitis, where cumulative lung damage prevents the body's normal ability to clear particles, the airways swell and make excessive mucus, and eventually areas die off and leave "dead space." In a smoker, other symptoms with the cough may raise concern about a lung infection or even cancer.
• Does she have other health risks or conditions? If she has been incarcerated or in a shelter, or perhaps is from a resource-poor country, we consider tuberculosis (TB). If she has a weakened immune system as well, due to HIV or long-term use of corticosteroids, TB and a host of other unusual organisms are on the list.
• Are we stumped? Rare conditions to consider include pulmonary fibrosis, sarcoidosis, autoimmune diseases, and anatomical abnormalities. Additional workup should include pulmonary and ENT evaluations.

Beyond the usual — and even the "unusual" — suspects

But what do we do for patients who either do not respond to treatments for their common conditions, or for whom extensive evaluation rules out the less common causes of a chronic cough? Well, researchers are now describing a new family of breathing and cough conditions caused by nerve dysfunction.

New evidence suggests that postnasal drip, acid reflux, or even forceful coughing in and of itself can aggravate nerve endings in the "cough centers" of the airways. These aggravated nerve endings then overreact to many other triggers, such as smoke, perfume, or temperature changes, causing an overwhelming urge to cough. They label this condition "neuronal hyper-responsiveness syndrome" and outline several approaches to treatment.

But wait, there's more. Other researchers describe a similar concept at the level of the larynx, a family of disorders under "laryngeal dysfunction syndrome" that can include "laryngeal hyper-responsiveness." Many of the treatments they describe are similar to the treatments for "neuronal hyper-responsiveness," and the most promising include the anticonvulsants gabapentin and pregabalin, the antidepressant amitriptyline, speech therapy, or a combination of these.

Basically, medical experts are describing a new cause of chronic cough based on aggravated nerves and airway dysfunction, and more research will result in better treatments.

Image: Alen-D/Getty Images