For the purposes of differential diagnosis, cough has been subdivided into acute and chronic, although this distinction is primarily used to separate the self-limited syndromes of acute bronchitis and upper respiratory infection (URI) from other causes. For the purposes of discussion, chronic cough is defined as a cough that is present for more than 3 weeks without any periods of resolution. Cough has also been divided into nonproductive and productive with excess sputum production. That distinction may be artificial because, at least for cases of chronic cough, the same disorders produce both nonproductive and productive coughing; the distinction is without diagnostic utility.13
Excluding environmental exposures, acute cough is most often due to URI, lower respiratory tract infection, and allergic reactions. Common URIs are associated with a combination of rhinorrhea, sinusitis, pharyngitis, and laryngitis, with the cough due to drainage from the nasopharynx onto cough receptors in the pharynx and larynx. A productive cough is the hallmark of acute bronchitis. While pneumonia generally produces a cough, pulmonary secretions may be scant; thus, the cough is not productive and the presentation may be dominated by other symptoms (e.g., altered mental status, fever, and dyspnea). Mycobacterial and fungal pulmonary infections may produce cough, but the presentation is usually more subacute or chronic. Acute asthma is often associated with cough, but symptoms of wheezing and dyspnea usually dominate. Occasionally, a patient with asthma may present with coughing, as opposed to wheezing, as a manifestation of airflow obstruction.
Chronic cough is due to a wide variety of disorders, but studies have found that most patients have chronic cough due to (1) smoking, often with chronic bronchitis, (2) postnasal discharge, (3) asthma, (4) gastroesophageal (GE) reflux, and (5) angiotensin-converting enzyme (ACE) inhibitor therapy ( Tab.l.® 58-4.).1 15 and 16 The association of smoking, chronic bronchitis, and persistent cough is so obvious as to merit little discussion, other than to firmly point it out to patients. Smoking-induced coughing is usually worse in the morning and, with chronic bronchitis, usually productive. Rhinitis with postnasal discharge is associated with mucus drainage from the nose, a history of "allergies or sinus problems," and frequent clearing of the throat or swallowing of mucus. Chronic cough associated with asthma is usually worse at night, exacerbated by irritants, and associated with episodic wheezing and dyspnea. Asthma can be exacerbated by b-blocker therapy and present with nocturnal coughing. Cough associated with GE reflux often has a history of heartburn, is worse when lying down, and improves with antiacid therapy (antacids or H 2 blockers).
The incidence of ACE inhibitor cough is approximately 10 to 12 percent, although higher values have been published. 17 All ACE inhibitors have been reported to induce cough; it is not clear whether certain agents have a higher likelihood of inducing cough than others. ACE inhibitor cough is thought to result when the blockade of ACE leads to accumulation of bradykinin and substance P, which stimulate the pulmonary cough receptors and enhance the formation of irritating prostaglandin metabolites. Extreme variability characterizes ACE inhibitor cough: early (1 week) or later (1 year) onset after starting treatment, only slightly bothersome to debilitating symptoms, and variation during the day. The association of pertussis in adults with persistent cough (>2 weeks) was documented from a convenience sample from one emergency department.18 The therapeutic implication of this finding is unclear; antibiotic treatment of adults with pertussis is controversial, and late treatment has no proven benefit. Tabje.5" lists the major causes of cough.
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