NCBI Bookshelf. A service of the National Library of Medicine, National Institutes of Health.
StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-.
Sandeep Sharma ; Muhammad F. Hashmi ; Mohamed S. Alhajjaj ; Jessica E. Knizel .
Last Update: August 8, 2023 .
A cough is one of the most common medical complaints accounting for as many as 30 million clinical visits per year. Up to 40% of these complaints result in referral to a pulmonologist. A cough is an innate primitive reflex and acts as part of the body’s immune system to protect against foreign materials. Coughing is associated with a wide assortment of clinical associations and etiologies. Furthermore, there are no objective tools to measure or clinically quantify a cough. As such, evaluation of a cough is initially a subjective and highly variable assessment. Given the vagueness of this symptom’s nature, along with the risk of an insidious underlying etiology, heavy impact on quality of life, and a lack of objective tools, coughing should be evaluated and treated as an important issue until a benign source is isolated.
The etiology of a cough is an arbitrary classification based largely on the duration of a cough. If a cough is presently less than three weeks, it is designated as acute. If a cough is present 3 to 8 weeks, it is designated as subacute. If a cough is presently greater than 8 weeks, it is designated as chronic.
The most common causes of acute cough in adults are an acute viral upper respiratory infection, also known as the common cold, and acute bronchitis. Acute bronchitis is typically viral in etiology, but bacterial infection is the source in approximately 10% of cases. Additional common causes of an acute cough include acute rhinosinusitis, pertussis, acute exacerbations of chronic obstructive pulmonary disorder, allergic rhinitis, asthma, congestive heart failure, pneumonia, aspiration syndromes, and pulmonary embolism.
Acute rhinosinusitis is characterized by an inflammation of the lining of the paranasal sinuses and accounts for approximately 16 million office visits per year. It is commonly due to a viral illness if present less than 10 days, but may be related to bacterial infection if the illness is longer than ten days. A cough is induced here, primarily as a response to increased mucus production and post-nasal drip.[1]
Pertussis, also known as whooping cough, is an illness with a classic clinical finding of paroxysmal episodes of intense coughing lasting up to several minutes followed by a loud gasp for air. It is an infection of the respiratory tract by Bordetella pertussis where the bacterium induces mucopurulent sanguineous exudate formation within the respiratory tract. The overall course of pertussis infection lasts up to 6 weeks and is characterized by 3 stages: a catarrhal phase, a paroxysmal phase, and a convalescent phase. The catarrhal phase is characterized by rhinorrhea, sneezing, low fever, tearing, and nasal congestion. The paroxysmal phase occurs within 2 weeks of colonization and is characterized by the classic coughing episodes followed by post-tussive vomiting. The convalescent phase is a condition of chronic coughing that may last for weeks. This illness is a serious diagnosis which requires prompt attention as it remains one of the highest causes of infant morbidity and mortality.[2]
Asthma is a complex disease where the body’s immune system is hyperresponsive to an environmental stimulus and results in inflammation, intermittent airflow obstruction, and bronchial hyperreactivity with constriction of the airways. It impacts 26 million people in the United States. A cough is induced in these patients as a result of increased mucous secretions compounded with narrowing of the airways.[3][4]
Acute exacerbations of chronic obstructive pulmonary disorder (COPD) are estimated to affect 32 million people in the United States alone. COPD is a classic triad of chronic bronchitis, emphysema, and asthma. These patients have a loss of lung elasticity as well as air trapping pathologies. This predisposes them to develop infections such as acute bronchitis and bacterial pneumonia. When an acute exacerbation occurs, the lung parenchyma becomes inflamed and has increased hyperresponsiveness leading to a constriction of the airways with a subsequent decline in lung function. This induces an accumulation of purulent and thick mucus secretions within the bronchioles and alveoli triggering a coughing response.[5]
Allergic rhinitis is an inflammation of the nasal mucosa secondary to an allergic irritation from the environment. This irritation leads to increased mucus secretion and post-nasal drip. It is the post nasal drip that irritates the airways, stimulating a cough.
Congestive heart failure is an illness where the heart’s efficiency in pumping blood has decreased to the point that fluid congestion begins to occur in the vasculature. Most commonly, this failure begins in the left ventricle and atria. Fluid congestion then occurs into the pulmonary vasculature. This creates edematous, heavy lungs with an increased A-a gradient and irritates the lungs, stimulating the cough.[6]
Pneumonia has many different etiologies and may be viral or bacterial. Viral pneumonia leads to inflammation and irritation of the airways, whereas bacterial pneumonia will also have increased mucous and purulent secretion irritating the airways further.
Aspiration syndromes occur when the glottis does not close sufficiently during swallowing. This allows for passage of food or fluid particles into the airways, rather than the esophagus. In addition, to be caustic and irritating, food particles may lead to an infectious pathology known as aspiration pneumonia.
A pulmonary embolism is a pathology where an embolus forms and becomes lodged within the pulmonary capillaries. Most commonly, this occurs as a deep vein thrombosis elsewhere in the body, which becomes dislodged and travels to the pulmonary circulation.[7]
Coughing develops here in a similar fashion to congestive heart failure. Blood congestion occurs in the areas before the embolus causing edematous and heavy lung spaces. This inflames and irritates the lung spaces. Additionally, if an embolus is large enough and present for a long enough period, necrosis of tissue may occur, releasing pro-inflammatory cytokines into the lung spaces, thus further worsening a cough.
Subacute coughing is most commonly post infectious secondary to continued irritation of cough receptors via ongoing or resolving bronchial or sinus inflammation from a preceding viral upper respiratory infection. Both acute and subacute coughs are self-limiting illnesses that typically require only supportive measures.
A chronic cough is a more difficult diagnosis to elucidate and typically will require referral to a cough specialist or a pulmonologist for evaluation. Possible causes include upper airway cough syndrome, gastroesophageal reflux disease, non-asthmatic eosinophilic bronchitis, chronic bronchitis, postinfectious cough, intolerance to angiotensin-converting enzyme inhibitor medication, malignancy, interstitial lung diseases, obstructive sleep apnea, chronic sinusitis, and psychosomatic cough.
Upper airway cough syndrome is the most common etiology of a chronic cough. There is a wide spectrum of illnesses that encompass this disease including allergic rhinitis, non-allergic rhinitis, post-infectious, and/or bacterial or viral rhinosinusitis. Essentially, upper airway cough syndrome is a longstanding post nasal drip that irritates the upper airway, inducing cough.[8]
Gastroesophageal reflux disease accounts for up to 40% of chronic coughs and occurs as a result of retropulsion of acidic contents from the stomach into the pharynx and larynx. This leads to irritation of laryngeal receptors and episodic microaspiration. Often, this illness will have a cough that is worse in the evenings, when the patient is lying flat as this allows for easier reflux of the stomach.[9][10]
Non-asthmatic eosinophilic bronchitis is an illness of hyperresponsiveness of the bronchioles without classic asthma findings and has an increased eosinophilic component indicating a hyperactive immune system. Hyperactive eosinophilia leads to increased concentrations of inflammatory cytokines, causing inflammation and irritation of the airways. Eosinophilic asthma varies from non-asthmatic eosinophilic bronchitis due to a difference in localization of mast cells within the airway wall. Smooth muscle infiltration occurs in typical asthma with narrowing of the airways as a result. There is epithelial infiltration of non-asthmatic eosinophilic bronchitis irritating cough receptors directly.
Chronic bronchitis is by definition a cough that has been present for longer than 3 months consecutively over 2 years. A cough is commonly present here as a result of excessive mucous secretions causing mucous plugging of the airways. An inflammatory component has also been suggested in this etiology. Chronic bronchitis does not have an infectious component; however, it predisposes the patient to have bacterial infections which may worsen the illness creating a positive feedback loop of coughing.
A post-infectious cough occurs due to increased cough receptor sensitivity and temporary bronchial hyperresponsiveness during the recovery from a worse pulmonary infection. This is likely closely related to developed epithelial damage from the initial pathology.
Cough variant asthma presents primarily with coughing, not wheezes as in typical asthma. These patients will have normal spirometry at baseline, but positive methacholine challenge, when tested. This should be suspected if a cough is non-productive, repetitive, occurs day and night, and is exacerbated by exercise, cold air, or upper respiratory infection. Look for positive family history or seasonal variation. This is thought to be because cough receptors are more prevalent in the proximal airways and decrease in density as the airways get smaller. Therefore, in cough variant asthma the inflammation is more prominent in the proximal airways where a cough is stimulated, and less so distally, where inflammation and narrowing would cause wheezing and dyspnea. Treatment is the same for cough variant asthma as for typical asthma.
Malignancy may cause a mass effect with physical obstruction or collapse of the airways, thus inducing mucus accumulation and secondary infections in addition to irritation of the cough receptors directly. Additionally, some cancers may have secretory effects into the airways.
Interstitial lung diseases are a large group of disorders which cause progressive scarring and hardening of lung tissue. These occur as the result of long-term exposure to various hazardous materials, such as asbestos, silicone, coal dust, radiation, or heavy metals. This is often work related such as in nuclear power plant workers, coal miners, sandblasting workers, and the like. Some types of autoimmune diseases including rheumatoid arthritis, scleroderma, dermatomyositis and polymyositis, mixed connective tissue disease, Sjogren syndrome, and sarcoidosis can cause interstitial lung disease. Additionally, idiopathic pulmonary fibrosis may occur.[11]
Obstructive sleep apnea is characterized by a partial or complete obstruction of the airway transiently during sleep. This increase in airway resistance causes a reflexive diaphragmatic and chest muscle spasm and cough to open the obstructed airway and pull air into the lungs. This typically occurs as a result of lax musculature in the pharynx or due to the increased weight of the neck collapsing the pharynx in obese people.[12]
Chronic sinusitis induced cough chronically as a result of prolonged inflammation and irritation of the sinus and nasal mucosa with purulent discharge secondary to a bacterial pathogen. This occurs as a result of recurrent acute sinusitis that allows for facultative anaerobic pathogens such as Staphylococcus aureus, Staphylococcus epidemicities, and other gram-negative organisms to flourish.
A psychosomatic cough is rarely diagnosed and as an etiology should be avoided unless no other explanation can be elucidated. This is the act of coughing as a habit rather than as part of a disease process. It may be learned as a habit or part of an underlying psychological condition.
A cough is the single most prevalent symptom on presentation to a physician’s office. Prevalence is heavily influenced by the social history of smoking tobacco usage and is estimated between 5% to 40%. The exact etiology of a cough determines the predilection of race and gender impact.
As with any illness, a full and detailed history collection accompanied with an appropriate physical exam is the most important aspect of any medical evaluation. Diagnosis of a cough is an obvious, clinical observation. A cough is a symptom, rather than a diagnosis of disease. As such, many patients present for evaluation of the secondary or underlying effects of a cough rather than a cough itself. Essential components of the history taking session should include:
