COUGH

Many studies have shown that coughing is the most disruptive respiratory symptom. All other respiratory symptoms such as runny or plugged nose, sneezing, difficulty breathing, wheezing are all considered far less significant by patients. Coughing not only can disrupt daytime activities and nighttime sleeping, but will often disrupt sleeping for an entire family in the case of children with persistent coughing. Severe coughing can also result in pulled muscles in the chest wall, fractures or dislocations in the ribs or rib cartilage, swelling and small red spots appearing on the face, and bleeding from the lungs (hemoptysis).

It is important to understand a little bit of the physiology behind coughing. Coughing is a protective reflex that prevents us breathing in particles from the throat (food) and moves excess mucus from the lower airway. There are small nerve endings in the back of the throat and in all the respiratory lining from the top of the lower airway (larynx) down to the smallest tubes in the lungs. When these nerve endings are stimulated they trigger off the cough reflex. The cough reflex results in air being moved out through the tubes in the lungs and into the throat at extremely high velocity. This high velocity air movement carries particles out of the airways. It is also important to know that individuals vary tremendously in the sensitivity of their own cough reflex. This is been studied extensively. Some individuals can suppress their cough reflex and only cough when they wish. Other individuals can never control their cough reflex and even minor stimulation results in coughing.

There are several common causes of persistent coughing. By far the most common is a simple viral respiratory infection. The infection causes excess mucus in the airways and the infection directly causes inflammation in the lining of the airways that irritates the nerve endings and makes many individuals cough more frequently and more severely. Usually this type of coughing disappears within seven to 14 days, although specific respiratory infections (pertussis, parapertussis, and some viral infections) can cause coughing which persists for many weeks. In a very similar way, allergic inflammation in the airway can cause excess mucus production and irritate the nerve endings that trigger the cough reflex, setting the individual up for increased persistent coughing. The allergic inflammatory process can exist in the larynx (allergic laryngitis) where you usually get coughing and a change in voice quality or actual loss of voice. The allergic inflammation can extend into the trachea (the largest tube in the lower airway) resulting in allergic tracheitis. In this instance you get only coughing with very little mucus production. If the allergic inflammatory process extends further into the larger bronchi you usually end up with coughing and mucus production. If the allergic inflammatory process extends into the medium and small airways (asthma), in addition to cough and mucus production, the individual experiences episodic difficulty breathing or wheezing. Allergy can involve one or more areas in the airways, while skipping other areas. Every individual varies in the amount of coughing versus the amount of mucus production and these two variables can change over time in the same individual. The upper respiratory airway can commonly cause coughing. Excess mucus from the sinuses (allergic sinusitis, chronic sinusitis, etc.) always goes down the back of the throat as post-nasal drip (PND). Individuals with PND frequently-repetitively clear their throat. This allows them to swallow the excess mucus coming down the back of the throat from the sinuses. Some of these individuals have their cough reflex triggered off when the mucus is in the back of the throat. This can occur in some individuals chronically, in some individuals when the mucus production becomes excessive, and in some individuals only at night when the mucus tends to build up in the back of the throat. Exposure to irritants can induce persistent coughing. Many inhaled chemicals (acids, caustic compounds, combustion products, etc.) can induce severe coughing. Certain chemicals have been specifically designed to induce coughing such as pepper spray. By far the most common chemical irritant is tobacco smoke. ETS (second hand tobacco smoke) is composed of over 4000 different chemicals. This can be a huge problem for individuals with a sensitive cough reflex. Individuals who smoke for a significant amount of time often have a persistent productive cough (especially in the morning). Smoking can lead to COPD and chronic bronchitis and a permanent chronic cough. This type of cough can start after years of smoking without having significant coughing previously. Individuals with acid reflux can experience chronic cough. The acid produced in the stomach (to dissolve food) can move backwards (reflux) up the lower esophagus. The acid stimulates nerves in the lower esophagus. These nerves arise from a similar area in the brain as the nerves that trigger the cough reflex. When these esophageal nerves are stimulated the individual coughs. These individuals do not necessarily have to have any symptoms of “heartburn” (about 30% have no “heartburn”), but the acid reflux still results in coughing. These represent the common causes of coughing. There are many other causes of chronic-persistent coughing that are not as common and will not be dealt with here. However, note should be made of the older individual that has a history of smoking where the possibility of lung cancer exists.

One of the most important concepts to be aware of, is that it is very common for more than one cause of coughing to exist in the same individual. There is an unusually high amount of reflux in asthmatics. The reasons for this are unknown at this time. Needless to say, any individual with asthma and acid reflux that also smoked and developed a respiratory infection, would be very likely to end up with a persistent cough. This concept of combined-multiple causes of coughing explains the way we usually go about treating an individual with persistent cough.

We have some sophisticated tests that can look into the airways, look into the esophagus and stomach, measure stomach acid production and acid reflux, etc. Most of these tests are expensive, time-consuming, and moderately invasive with associated risks. We usually diagnose the cause of coughing by initiating specific directed treatment at one cause. If this treatment significantly improves the individual's coughing then this particular cause was contributing to the persistent cough. We have highly specific treatment for allergic tracheitis-bronchitis-asthma. If standard asthma inhalers eliminate coughing, particularly if there is elimination of mucus production, improvement in exercise capacity, and improvement in lung function (PFT) the diagnosis of asthma or allergic airway disease is made. Singulair, an oral medication that was developed for asthma, reduces mucus production and inflammation (and therefore coughing) in the entire airway (nose-sinuses-lower airway). So Singulair can help individuals with a combination of post nasal drip-allergic laryngitis-tracheitis-bronchitis-asthma. Unfortunately, the response to Singulair is genetically determined and only 50% of individuals get a beneficial response. Half the individuals who try Singulair have absolutely no improvement. If a specific single allergen can be identified that is driving the allergic inflammation (i.e. a cat, dust mites, etc.), then appropriate avoidance measures can eliminate the inflammation and cough. Normally, individuals are allergic to multiple allergens, and avoidance measures form part of the treatment plan along with medication. If it is likely that post nasal drip (PND) is causing coughing, highly directed treatment at PND (usually a combination of high dose antihistamines, decongestants, and nasal corticosteroids sprays) can significantly reduce PND and improve coughing. I would like to note however, that PND is difficult if not impossible to eliminate in most individuals as we cannot get medication directly into the sinuses to treat the inflamed sinus respiratory lining. If the individual has a sinus infection (acute or chronic) then treatment with an antibiotic often brings about significant resolution of PND. We have newer highly selective potent medications to reduce acid production in the stomach. If acid reflux is felt to be a possibility, a short trial on one of these acid suppressants will bring about significant improvement in cough if reflux is indeed playing a role (and may be required in the long-term).

It is a combination of the history of coughing and the physical examination of the individual that leads me to try a specific directed treatment. In essence this type of treatment is “intelligent trial and error”. There have been multiple studies showing that this type of specific directed treatment can bring about more rapid resolution of chronic-persistent coughing and simultaneously produce the correct diagnosis. Hopefully, after reading this section, you will have a better appreciation of the causes and treatment of coughing.

Reprinted with permission - Dr. Bruce Sweet 2005