Chapter 034. Cough and Hemoptysis (Part 1) docx

Reasons for this include discomfort from the cough itself, interference with normal lifestyle, and concern for the cause of the cough, especially fear of cancer... Etiology Cough can be

Chapter 034 Cough and

Hemoptysis

(Part 1)

Harrison's Internal Medicine > Chapter 34 Cough and Hemoptysis

Cough

Cough is an explosive expiration that provides a normal protective mechanism for clearing the tracheobronchial tree of secretions and foreign material When excessive or bothersome, it is also one of the most common symptoms for which patients seek medical attention Reasons for this include discomfort from the cough itself, interference with normal lifestyle, and concern for the cause of the cough, especially fear of cancer

Mechanism

Coughing may be initiated either voluntarily or reflexively As a defensive

reflex it has both afferent and efferent pathways The afferent limb includes

receptors within the sensory distribution of the trigeminal, glossopharyngeal,

superior laryngeal, and vagus nerves The efferent limb includes the recurrent

laryngeal nerve and the spinal nerves The cough starts with a deep inspiration followed by glottic closure, relaxation of the diaphragm, and muscle contraction against a closed glottis The resulting markedly positive intrathoracic pressure causes narrowing of the trachea Once the glottis opens, the large pressure differential between the airways and the atmosphere coupled with tracheal narrowing produces rapid flow rates through the trachea The shearing forces that develop aid in the elimination of mucus and foreign materials

Etiology

Cough can be initiated by a variety of irritant triggers either from an exogenous source (smoke, dust, fumes, foreign bodies) or from an endogenous origin (upper airway secretions, gastric contents) These stimuli may affect receptors in the upper airway (especially the pharynx and larynx) or in the lower respiratory tract, following access to the tracheobronchial tree by inhalation or aspiration When cough is triggered by upper airway secretions (as with postnasal drip) or gastric contents (as with gastroesophageal reflux), the initiating factor can

go unrecognized and the cough may persist Additionally, prolonged exposure to such irritants may initiate airway inflammation, which can itself precipitate cough

and sensitize the airway to other irritants Cough associated with gastroesophageal reflux is due only in part to irritation of upper airway receptors or to aspiration of gastric contents, as a vagally mediated reflex mechanism secondary to acid in the distal esophagus may also contribute

Any disorder resulting in inflammation, constriction, infiltration, or compression of airways can be associated with cough Inflammation commonly results from airway infections, ranging from viral or bacterial bronchitis to bronchiectasis In viral bronchitis, airway inflammation sometimes persists long after resolution of the typical acute symptoms, thereby producing a prolonged cough that may last for weeks Pertussis infection is also a possible cause of persistent cough in adults; however, diagnosis is generally made on clinical grounds (Chap 142) Asthma is a common cause of cough Although the clinical setting commonly suggests when a cough is secondary to asthma, some patients present with cough in the absence of wheezing or dyspnea, thus making the diagnosis more subtle ("cough variant asthma") A neoplasm infiltrating the airway wall, such as bronchogenic carcinoma or a carcinoid tumor, is commonly associated with cough Airway infiltration with granulomas may also trigger a cough, as seen with endobronchial sarcoidosis or tuberculosis Compression of airways results from extrinsic masses such as lymph nodes or mediastinal tumors,

or rarely from an aortic aneurysm

Examples of parenchymal lung disease potentially producing cough include interstitial lung disease, pneumonia, and lung abscess Congestive heart failure may be associated with cough, probably as a consequence of interstitial as well as peribronchial edema A nonproductive cough complicates the use of angiotensin-converting enzyme (ACE) inhibitors in 5–20% of patients taking these agents Onset is usually within 1 week of starting the drug but can be delayed up to 6 months Although the mechanism is not known with certainty, it may relate to accumulation of bradykinin or substance P, both of which are degraded by ACE

In contrast, angiotensin II receptor antagonists do not seem to increase cough, likely because these drugs do not significantly increase bradykinin levels

The most common causes of cough can be categorized according to the duration of the cough Acute cough (<3 weeks) is most often due to upper respiratory infection (especially the common cold, acute bacterial sinusitis, and pertussis), but more serious disorders, such as pneumonia, pulmonary embolus, and congestive heart failure, can also present in this fashion Subacute cough (between 3 and 8 weeks) is commonly post-infectious, resulting from persistent airway inflammation and/or postnasal drip following viral infection, pertussis, or

infection with Mycoplasma or Chlamydia In the patient with subacute cough that

is not clearly post-infectious, the varied causes of chronic cough should be considered Chronic cough (>8 weeks) in a smoker raises the possibilities of chronic obstructive lung disease or bronchogenic carcinoma In a nonsmoker who

has a normal chest radiograph and is not taking an ACE inhibitor, the most

common causes of chronic cough are postnasal drip (sometimes termed the upper

airway cough syndrome), asthma, and gastroesophageal reflux Eosinophilic

bronchitis in the absence of asthma has also been recognized as a potential cause

of chronic cough