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Persistent Coughing: Unyielding Symptoms and Expert Advice

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Understanding Chronic Cough: Causes and Treatment Approaches

It's safe to assume that almost everyone has experienced a cough at some point in their lives. Often, it's a temporary annoyance that goes away on its own. However, chronic cough, persisting for at least eight weeks, can be challenging to manage for both patients and doctors alike.

In the October 20, 2016 issue of the New England Journal of Medicine, lung experts explore a step-by-step approach that doctors can adopt to effectively treat patients struggling with chronic cough. While the majority of prolonged cough cases can be attributed to common causes, the complex nature of a chronic cough demands a thorough examination to rule out rarer conditions. Interestingly, experts now recognize that overactive nerves can be the underlying culprits behind an exaggerated cough response to certain triggers.

The "Usual Suspects" of Chronic Cough

Let's paint a picture of a typical patient with a chronic cough, someone I often encounter in my practice. We have a middle-aged woman who has been dealing with a persistent cough for several months. Naturally, we, as doctors, begin by asking numerous questions to gather relevant information.

  • Has she been experiencing chronic allergy symptoms like itchy, watery eyes, a runny nose, and postnasal drip? If so, we may recommend trying antihistamines and nasal steroids. Untreated allergies can lead to chronic sinus infections, resulting in a cough caused by postnasal drip, so addressing this aspect becomes crucial.
  • Could her cough be a manifestation of "cough variant" asthma, which doesn't involve wheezing? To save my patients time and avoid unnecessary tests, I often initiate treatment with inhalers if cough-variant asthma is suspected. Administering inhaled albuterol to open the airways and a steroid inhaler to reduce inflammation can help diagnose and address the issue simultaneously.
  • Is she experiencing symptoms of heartburn? Acid reflux is another potential trigger for cough, and if the patient describes heartburn symptoms or if the cause of the cough remains uncertain, we may prescribe eight weeks of acid-lowering medication.
  • Is she taking any medications known to cause coughing as a side effect? Certain blood pressure medications from the ACE inhibitor class, such as Lisinopril, can lead to coughing in approximately 20% of patients. Temporarily discontinuing this medication could be considered to assess its impact on the cough.
  • Is she among the 17% of Americans who smoke? If so, chronic bronchitis due to cumulative lung damage becomes a concern. The impaired lung function hampers the body's ability to clear particles, causing airway swelling, excess mucus production, and potential complications like lung infection or even lung cancer.
  • Does she have any other underlying health risks or conditions? Considering potential tuberculosis (TB) infections is crucial if the patient has a history of incarceration, shelter residency, or hails from a resource-poor country. Furthermore, individuals with weakened immune systems (due to HIV or long-term corticosteroid use) may be prone to TB and other unusual infections.
  • Are we still unable to identify the cause of the cough? At this point, rare conditions like pulmonary fibrosis, sarcoidosis, autoimmune diseases, and anatomical abnormalities should be considered. Further evaluation from pulmonologists and ear, nose, and throat specialists is warranted.

The Perplexity of Chronic Cough

Who hasn't experienced the frustration of a persistent cough? It's a common complaint that brings patients to the clinic on a regular basis. However, chronic cough, lasting eight weeks or longer, can be challenging for both patients and doctors to tackle.

In the October 20, 2016 issue of the New England Journal of Medicine, experts in the field of lung health present a step-by-step approach for physicians to effectively treat patients with chronic cough. While most prolonged cough cases have well-known causes, there are instances where the root cause remains elusive. In those cases, a comprehensive list of increasingly rare conditions should be considered and eliminated. Interestingly, experts now acknowledge that overactive nerves could be at the root of exaggerated cough responses to specific triggers.

The Extensive Search for Answers

The authors introduce a typical patient scenario involving a middle-aged woman who has been plagued by a persistent cough for several months. To better understand the situation, thorough questioning is essential.

1. Chronic Allergy Symptoms

One line of investigation focuses on exploring chronic allergy symptoms, such as itchy, watery eyes and nose, stuffy nose, and postnasal drip. If these symptoms are present, it may be worth considering antihistamines and nasal steroids as a potential treatment option. Neglected allergies can lead to chronic sinus infections, which can trigger coughing due to postnasal drip. Thus, treating these underlying allergies may alleviate the cough.

2. Cough-Variant Asthma

Another possibility that cannot be overlooked is "cough-variant" asthma, which causes a persistent cough without wheezing. Some patients prefer not to wait for a consultation with a lung specialist or undergo complex tests. If cough-variant asthma is suspected, inhalers can be a straightforward and effective solution. Inhaled albuterol, which helps open the airways, and a steroid inhaler to reduce inflammation not only aid in diagnosing the condition but also provide relief from the persistent cough.

3. Acid Reflux

Heartburn symptoms may also play a significant role in chronic coughing. Acid reflux, when stomach acid flows back into the esophagus, can trigger coughing. In cases where heartburn symptoms are reported or if the cause of the cough remains uncertain, prescribing an acid-lowering medication for eight weeks is a common approach.

4. Medication Side Effects

It is important to consider whether the patient is taking any medications that list coughing as a potential side effect. For example, ACE inhibitors, a class of blood pressure medications, can cause coughing in approximately 20% of patients. In these situations, a trial period without the medication may be warranted to determine if it is the cause of the persistent cough.

5. Smoking

In cases where the patient is among the 17% of Americans who smoke cigarettes, chronic bronchitis may be the culprit. Smoking can lead to cumulative lung damage, impairing the body's ability to clear particles. This damage causes the airways to swell and produce excessive mucus. Furthermore, it can result in the formation of "dead space" areas in the lungs. Considering the possibility of a lung infection or even cancer is crucial when other symptoms accompany the persistent cough in smokers.

6. Other Health Risks and Conditions

In patients with other health risks or specific conditions, additional investigations are required. Those who have been incarcerated, lived in shelters, or come from resource-poor countries may be at risk for tuberculosis (TB). If the patient also has a weakened immune system due to conditions like HIV or long-term corticosteroid use, TB and other uncommon organisms should be considered as potential causes. A pulmonary and ENT evaluation may be necessary.

7. When All Else Fails

For patients who do not respond to treatments for common conditions or have been thoroughly evaluated to rule out less common causes, researchers have identified a new category of breathing and cough conditions linked to nerve dysfunction.

Recent evidence suggests that postnasal drip, acid reflux, or forceful coughing itself can agitate nerve endings in the "cough centers" of the airways. These aggravated nerve endings become hypersensitive to various triggers, such as smoke, perfume, or temperature changes. As a result, an overwhelming urge to cough ensues. This condition is known as "neuronal hyper-responsiveness syndrome," and several treatment approaches have been outlined.

Another related concept that researchers have discovered is "laryngeal dysfunction syndrome." This family of disorders, which includes "laryngeal hyper-responsiveness," primarily affects the larynx. Many of the suggested treatments align with those for "neuronal hyper-responsiveness." Promising options include anticonvulsants like gabapentin and pregabalin, the antidepressant amitriptyline, speech therapy, or a combination of these approaches.

Medical experts are continuing to explore the connection between aggravated nerves, airway dysfunction, and chronic cough. As further research advances, better treatments and solutions for patients affected by this perplexing condition are expected to emerge.

Beyond the Usual Culprits: Unraveling Nerve Dysfunction

But what about patients who don't respond to treatment for common causes or when an extensive evaluation eliminates the less common factors? Recent studies unveil a novel category of breathing and cough disorders resulting from nerve dysfunction.

Evidence suggests that postnasal drip, acid reflux, or even forceful coughing can trigger nerve endings in the "cough centers" of the airways, leading to an exaggerated response. These agitated nerve endings become highly sensitive to various triggers such as smoke, perfume, or temperature changes, resulting in an overwhelming urge to cough. Researchers term this condition "neuronal hyper-responsiveness syndrome" and propose several treatment approaches.

Furthermore, researchers have identified a similar concept focused on the larynx, referring to a group of disorders as "laryngeal dysfunction syndrome" that includes "laryngeal hyper-responsiveness." Many treatments overlap with those for "neuronal hyper-responsiveness," and the most promising approaches involve anticonvulsants like gabapentin and pregabalin, the antidepressant amitriptyline, speech therapy, or a combination of these methods.

Evidently, medical experts are highlighting a new perspective on the causes of chronic cough by emphasizing nerve irritation and airway dysfunction. Further research in this area holds the potential for improved treatments and management options.

William H. McDaniel, MD

Dr. Robert H. Shmerling is the former clinical chief of the division of rheumatology at Beth Israel Deaconess Medical Center (BIDMC), and is a current member of the corresponding faculty in medicine at Harvard Medical School.

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