Diagnosis And Treatment Of Cough

Asthma should be suspected as the cause of chronic cough under any of three circumstances: (1) the patient complains of episodic wheezing, shortness of breath, and cough, and wheezing is heard on chest examination; (2) pulmonary function testing demonstrates reversible airflow obstruction, even in the absence of wheezing; or (3) methacholine inhalation challenge testing is positive in a patient with normal or near-normal results on routine spirometry, even in the absence of wheezing. Chronic cough can be the sole presenting manifestation of asthma (i.e., cough-variant asthma). In a prospective study of chronic cough, cough was the only symptom of asthma in 28% of the asthmatic group. Cough-variant asthma is important to recognize, not only so that the cough can be alleviated but also because airway remodeling occurs and these structural changes in the airway are an important target of asthma therapy. Nonspecific pharmacologic bronchoprovocation challenge testing is extremely helpful in ruling out asthma as a possible cause of cough. Although it only has a positive predictive value of 60% to 80%, it has a negative predictive value that approaches 100%. Therefore, a negative methacholine challenge essentially rules out asthma as a cause of chronic cough. An exception would be the patient who may have occupational asthma in its earliest stage. In such cases, however, the methacholine challenge should become positive as the workplace exposure continues. False positive results on methacholine challenge testing have been reported to occur in 22% of patients being evaluated for chronic cough. Therefore, it must be emphasized that a positive test, by itself (i.e., in the absence of a favorable response to therapy) is not diagnostic of asthma as the cause of cough. Because not all wheezes are from asthma and because the presence of bronchial hyperresponsiveness does not necessarily mean that asthma is the cause of cough, the diagnosis of asthma as the cause of chronic cough requires that the cough respond to specific therapy for asthma and that the patient's subsequent clinical course is consistent with asthma. In this regard, the diagnosis of asthmatic cough is not made in any patient who has experienced an obvious respiratory tract infection within the previous 2 months, because cough and bronchial hyperresponsiveness can be transient and self-limited in this setting.

Cough is a well-known side effect of ACE inhibitors. The pathogenesis may be related to bradykinin sensitization of afferent sensory nerves in the airways. Stimulation of cough appears to be a class effect of these drugs and is not dose related. In patients who experience a cough with one ACE inhibitor, cough usually develops when another ACE inhibitor is substituted. Although the reported frequency of cough associated with ACE inhibitors has varied widely, from 0.2% to 33%, prospective studies have shown that ACE inhibitors account for 2% of chronic cough. Cough has been reported to appear within a few hours of taking a first dose in many patients, but it may not become apparent for weeks, months, or even longer. In a prospective study of lisinopril rechallenge in patients who had previously experienced an ACE inhibitorâ??induced cough, the median time for cough to redevelop was 19 days, and the median time to resolution during placebo washout was 26 days. ACE inhibitor induced cough is diagnosed by stopping the drug and observing resolution of the cough.

GERD should be suspected as the cause of chronic cough whenever a patient complains of frequent episodes of typical gastrointestinal symptoms such as daily heartburn and regurgitation, especially when the chest radiograph or clinical picture suggests an aspiration syndrome. Chronic cough may be the only symptom of GERD; in prospective studies, such so-called silent GERD has accounted for 43% to 75% of cases. In the absence of gastrointestinal symptoms, chronic cough can be confidently attributed to GERD if the patient is a nonsmoker, is not taking an ACE inhibitor, has a normal or near-normal chest radiograph, and asthma, UACS, and nonasthmatic eosinophilic bronchitis have been ruled out; 92% of patients with silent GERD fit this clinical profile. Failure to obtain a history of nocturnal coughing does not exclude GERD as a cause of cough. When the chest radiograph is normal, cough from GERD most commonly occurs while the patient is awake and upright, and it usually does not occur or is not noted at all during sleep. Confirmation of GERD as the cause of cough requires that the cough disappear when the patient starts antireflux therapy. Nevertheless, if treatment with proton pump inhibitors fails to eliminate cough in a patient who fits the clinical profile for GERD-induced chronic cough, GERD may nevertheless be causing the cough, albeit through a nonacid mechanism. The precise mechanism by which GERD causes cough is not known. Although GERD can stimulate cough by irritating the upper respiratory tract without aspiration (e.g., larynx/hypopharynx) or by irritating the lower respiratory tract with aspiration, GERD appears to most commonly cause chronic cough by stimulating an esophageal-bronchial reflex in the mucosa of the distal esophagus.

B. pertussis should be considered as a possible cause of postinfectious cough, especially if B. pertussis infections have been recently reported in the community, the patient has a history of contact with a known case, the cough has followed a biphasic course (mild and nonproductive at first, then violently spasmodic), or the patient presents with the characteristic "whoop" or with a cough-vomit syndrome. Classically, B. pertussis infection has a 1- to 3-week incubation period; a catarrhal phase of conjunctivitis, rhinorrhea, fever, malaise, and cough; and then a paroxysmal phase, during which the cough worsens. Cough from pertussis usually lasts 4 to 6 weeks. The laboratory confirmation of B. pertussis in a clinical setting can be difficult to establish because there is usually a delay between the onset of cough and the suspicion of the disease and because there is no readily available, reliable serologic test for B. pertussis. Cultures of nasopharyngeal secretions are usually negative beyond 2 weeks of infection, and confirmatory serologic testing requires paired acute and convalescent sera samples. Polymerase chain reaction tests for B. pertussis have not yet been standardized. With postinfectious subacute cough from presumed or confirmed pertussis, antibiotic treatment may be helpful if prescribed within the first few weeks.