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.
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.
