Chronic cough is now defined as a cough that lasts for at least eight weeks. This is a multisys-tem condition causing complications such as anxiety, fatigue, insomnia, myalgia, dyspho-nia, and urinary incontinence. Approximately 1 percent of the population is affected by chronic cough, and it is now the fifth most common reason given for consultation with a primary care physician. The condition is particularly common in the elderly, school-aged children, and urban populations that are exposed to air pollution. A review by D'Urzo and Jugovic concludes that most cases can be attributed to postnasal drip syndrome, asthma, gastroesophageal reflux disease (GERD), or a combination of these conditions.
They used electronic searches to identify articles related to chronic cough plus secondary searches of the bibliographies of the articles identified. A total of 33 articles, mostly cohort studies and case reports, were used to prepare the review article.
In the patient with chronic cough, a careful history and targeted physical examination frequently confirm one of the most common causes (see accompanying figure), but post-nasal drip syndrome, asthma, and GERD can occur without classic symptoms or findings on physical examination. All patients should receive chest radiography, but other testing should be individualized, targeting the most probable etiology in each patient. Trial of treatment—empiric therapy for the most likely cause—may be preferable to extensive investigation because it may provide relief and diagnosis simultaneously.
The most common cause of chronic cough is postnasal drip syndrome, usually following viral infection of the upper respiratory tract. Other causes of chronic nasal inflammation, such as seasonal or allergic rhinitis, chronic sinusitis, medications, irritants, and excessive vasomotor responsiveness, can result in post-nasal drip syndrome and chronic cough. Patients report constant tickling or dripping in the back of the throat, which persists in spite of repeated attempts to clear it. Other symptoms include nasal congestion, rhinor-rhea, and hoarseness. In addition to treating the primary cause, postnasal drip syndrome usually requires a combination of a first-generation antihistamine such as dexbromphen-iramine and a decongestant such as pseudo-ephedrine. If improvement is not apparent within two weeks, other causes of chronic cough should be sought. First-generation antihistamines are effective because of their anticholinergic properties, but they are also responsible for side effects such as insomnia, anxiety, palpitations, hypertension, dry mouth and eyes and, possibly, urinary problems.
In approximately one half of all asthma cases, chronic cough is the only symptom, and cough-variant asthma should always be considered in chronic cough, even if the patient does not have other classic asthma symptoms such as wheezing, chest tightness, and dysp-nea. Patients with classic asthma have airway hyperresponsiveness and reversible airflow obstruction. Spirometry studies can establish the degree of airway obstruction by measuring forced expiratory volume in one second. Asthmatic patients show at least 12 percent reversibility in response to therapy. Cough-variant asthma is more difficult to document because reversible airflow obstruction is uncommon. Because the methacholine challenge test has a positive predictive value of 88 percent and a negative predictive value of 100 percent, a negative test rules out cough-variant asthma while a positive test does not conclusively diagnose the condition. The diagnosis is often based on response to therapy. Current treatment guidelines recommend the use of beta agonists and inhaled cortico-steroids, with the addition of oral steroids in severe cases. Most coughs resolve within six to eight weeks, at which time steroids can sometimes be discontinued.
Transient loss of tone in the lower esopha-geal sphincter is believed to result in acid reflux, causing irritation, inflammation, and coughing, which becomes a self-perpetuating cycle. Patients with microaspiration usually have symptoms of dysphonia, heartburn, and sore throat. Those with macroaspiration may have wheezing, dyspnea, and night sweats. Chronic cough also may result from vagal stimulation without symptoms of microaspi-ration. Chronic cough is often relieved with a combination of a proton pump inhibitor and a prokinetic agent plus weight reduction, smoking cessation, and dietary advice, but symptoms may take six months to resolve.