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CHRONIC COUGH


CHRONIC COUGH
Healthy people rarely cough. When they do, it is essentially devoid of any clinical significance. However, when cough is present and persistently troublesome, it can assume great clinical significance. Although cough can become an important factor in spreading infection, this is not the reason why it is one of the most common symptoms for which patients seek medical attention and spend money for medications. They do so because cough adversely affects their quality of life in a variety of ways related to the pressures, velocities, and energy that are generated during vigorous coughing. Although intrathoracic pressures up to 300 mm Hg, expiratory velocities up to 28,000 cm/sec or 500 mph (i.e., 85% of the speed of sound), and intrathoracic energy up to 25 J allow coughing to be an effective means of clearing excessive secretions and foreign material from the lower airways and providing cardiopulmonary resuscitation, these physiologic consequences can lead to physical as well as psychosocial complications. The gamut of complications ranges from cardiovascular, constitutional symptoms, gastrointestinal, genitourinary, musculoskeletal, neurologic, ophthalmologic, psychosocial, quality of life, respiratory, to dermatologic consequences.

CHRONIC COUGH

Urinary incontinence, rib fractures, syncope, and psychosocial complications such as selfconsciousness and the fear of serious disease are particularly bothersome. Coughing-induced urinary incontinence is particularly troublesome in women, especially as they age and in those who have delivered children. Coughing-induced rib fractures may occur in the absence of osteoporosis and typically posterolaterally where the serratus anterior muscle interdigitates with the latissimus dorsi muscle. Syncope caused by coughing can be sudden if the force of the cough causes a concussion wave in the cerebrospinal fluid or more gradual because of hypotension from a decrease in cardiac output.
The modern era of managing cough as a symptom was heralded by the description of a systematic manner of evaluating cough that was based on the putative neuroanatomy of the afferent limb of the cough reflex and the classification of cough based on its duration. Both concepts have been validated (Plate 4-10).
As originally proposed, systematically evaluating the locations of the afferent limb of the cough reflex (i.e., anatomic diagnostic approach) would have the best chance of leading to a correct diagnosis. Although involuntary coughing has traditionally been thought to be solely mediated via the vagus nerve, experimental data suggest that other nerves may also be involved. The anatomic diagnostic approach allowed for the discoveries of extrapulmonary causes of cough such as upper airway cough syndrome caused by a variety of rhinosinus conditions and cough caused by gastroesophageal reflux disease (GERD) without aspiration.
The classification of cough into acute (i.e., <3 weeks), subacute (i.e., 3-8 weeks), and chronic (i.e., <8 weeks) has become one of the most important parts of the workup of cough because it narrows the spectrum of potential diagnostic possibilities (Plate 4-10). The most common causes of acute cough include upper respiratory tract infections (URIs; e.g., the common cold), bacterial sinusitis, Bordetella pertussis infection, exacerbations of asthma, chronic bronchitis, allergic rhinitis, and environmental irritant rhinitis. The most common causes of subacute cough include postinfectious cough (e.g., after B. pertussis infection); bacterial sinusitis; and exacerbation of preexisting conditions such as asthma, rhinosinus diseases, bronchiectasis, and chronic bronchitis. The most common causes of chronic cough include upper airway cough syndrome caused by a variety of rhinosinus conditions, asthma, nonasthmatic eosinophilic bronchitis, GERD, chronic bronchitis, and bronchiectasis.
When the clinician systematically follows a validated diagnostic protocol and prescribes specific treatment in adequate doses directed against the presumptive cause(s) of cough, cough will improve or disappear in the great majority of cases. At least 20% of the time, chronic cough is caused by multiple conditions that simultaneously contribute. The causes of cough can only be determined when it responds to specific treatment.