Cough is a reflex physiological mechanism of the respiratory system that serves to protect the airways from inhaled and foreign body irritants and to cleanse them of retained secretions, but it can also be a common symptom of various diseases, both acute and chronic. It is a product of the stimulation of receptors at different points of the airway and in other locations, whose integration occurs at the level of the brain stem. According to its evolution over time, the cough can be acute or chronic.
Acute coughing episodes are not usually a diagnostic problem since most are due to respiratory tract infections, the most common cause being the common cold (acute rhinopharyngitis). On the other hand, chronic cough frequently constitutes a complex diagnostic problem, which generates a large number of consultations in clinical practice and involves costs in studies and disorders in the quality of life of patients.
Chronic cough is defined as that not linked to an acute process, which persists for more than three weeks, and whose etiology until then is unknown. Some authors consider a minimum time of eight weeks to talk about chronicity, because sometimes, cough linked to banal infections of the upper respiratory tract can last that long. Chronic cough presents a greater variety of causes that in turn are frequently associated.
Given that the adequate and successful treatment of chronic cough requires etiological identification, the first step in its management is to understand its causes, which will be analyzed later.
Cough is the result of a complex series of physiological reflexes that protect the lung from aspiration of harmful substances. It is defined as an explosive expiratory response to remove inhaled irritating material or substances from the airways. It can also be the manifestation of an illness or even a voluntary act.
Cough as a reflex act of defense requires an arc that begins with stimulation of the receptors, an afferent pathway that goes to the cough center and an efferent pathway that starts from it to the organs responsible for causing the cough. Cough receptors are present throughout the respiratory tract, but more concentrated where it is most effective, such as in the mucosa of the posterior wall of the pharynx, vocal cords, tracheal mucosa, mucosa of the carina and the bronchi of the higher caliber. Receptors have also been described in the paranasal sinuses, external auditory canal, in the tympanic membranes, the pleura, the pericardium, the diaphragm and the stomach. The lung parenchyma is devoid of cough receptors.
The stimuli capable of inducing cough are inflammatory, mechanical, chemical, thermal or psychogenic.
Inflammatory stimuli are triggered by edema or hypersecretion of the mucosa, irritation by exudates on the surface of the mucosa that are transmitted to the nerve endings, or by contraction of scar tissue that determines traction of those.
Mechanical stimuli are produced by the inhalation of certain particles, compression of the airways and tension on these structures. Compression injuries can be divided into extramural and intramural. Among the first ones, the aortic aneurysm, primary and secondary pulmonary neoplasms and mediastinal tumors stand out; The latter include bronchogenic carcinoma, carcinoid tumor, and other low-grade bronchial tumors, endobronchial metastases, foreign bodies, and endobronchial granulomas.
Chemical stimuli can be caused by inhalation of irritating gases, chlorine, and others. Tobacco smoke irritates the respiratory mucosa due to its chemical composition, with smoking being the most frequent cause of chemical stimulation of cough.
Within the thermal stimuli of cough, whether it is the inhalation of hot or very cold air, they are determining factors that occur more frequently on a tracheobronchial tree with a certain pathological basis (COPD, bronchial hyperreactivity, etc.).
Finally, psychogenic stimuli can be observed in patients with some underlying pathology or in healthy patients in whom it constitutes a mechanism to release nervous tension or stress.
Once any of these stimuli incite the sensory receptors of the trigeminal, glossopharyngeal, vagus and superior laryngeal nerve, depending on the stimulated cough zone, they send a message to the cough center in the bulb and it sends a message in response to the stimulus through of the superior laryngeal, phrenic and spinal nerves giving rise to the cough mechanism.
The cough process develops in 4 phases: 1) Phase of deep inspiration and opening of the glottis; 2) Compressive phase where there is contraction of the expiratory muscles and closure of the glottis with increased intrathoracic pressure; 3) Expiratory or expulsive phase where the glottis is opened and the air is expelled at enormous speed (up to 2500 cm / sec); 4) Rest phase, where relaxation of the expiratory muscles and re-expansion of the airways occurs.
Classifications and causes
According to its sound and symptomatic characteristics, cough can be broadly divided into 2 types, dry cough (without respiratory secretions) and wet cough accompanied or not by expectoration, which is associated with respiratory sounds secondary to the mobilization of secretions in the airways. Cough is productive when wet cough is followed by expectoration. Sometimes both types can coexist in the same patient. Other types of cough are described in turn, which are detailed below:
- Dry, irritative cough: characteristic of the first phase of acute tracheobronchitis and pleuritis, characterized by a dry cough that appears at the end of inspiration. It is a clear and resonant cough.
- Muted cough: it is a weak hue, due to muscular weakness or respiratory muscular paresis, typical of the elderly or younger people with neuromuscular pathologies.
- Quintosa cough: It is characterized by having five or more cough accesses that ends with a prolonged and wheezing inspiration (in surprise or trigger) and eliminates a thick, phlegm that can cause vomiting (emetic cough). It is typical of whooping cough.
- Coqueluchoid cough: It is similar to quintosa but it is not productive, it is less intense and less lasting and it appears in mediastinal syndromes due to compression of the vagus due to tumors or inflammatory processes that involve the vagus.
- Hoarse or doggy cough: It is intense and severe, similar to a dog's bark. It is typical of tracheitis and is accompanied by a sensation of retrosternal injury or wound.
- Aphonic cough: It is characterized by being low-pitched and due to inflammatory or neoplastic or destructive lesions of the vocal cords.
- Bitonal cough: It is a cough with two tones of sounds and accompanied by a bitonal voice, due to paralysis of a vocal cord, more frequently the left, caused by aneurysms of the aortic arch, mediastinal or lung tumors that compromise the recurrent nerve.
According to the evolution over time, cough has been arbitrarily divided into acute and chronic (categories that are not mutually exclusive), depending on whether it lasts less or more than 3 weeks, for the purposes of its best study and treatment. However, some authors, as already mentioned initially, set a limit of 8 weeks to start talking about chronic cough because they consider that acute infectious processes of the upper respiratory tract can produce cough during that period of time.
Most frequent causes of acute cough: Although innumerable, some of the most frequent are:
- Common cold
- Acute trachebronchitis
- Bronchial asthma
- Irritative or allergic
- Allergic rhinitis
- Inhalation of toxic fumes or gases
- Pulmonary embolism
- Heart failure
Most frequent causes of Chronic Cough:
- Chronic post-nasal drip
- Chronic bronchitis (COPD)
- Bronchial asthma
- Carcinoma broncogénico
- Gastroesophageal reflux
- Drugs (ACEI)
- Pulmonary tuberculosis
- Psychogenic (diagnosis of exclusion)
- Interstitial lung disease
- Occupational exposure to gases or fumes
- Lung metastases
- Congestive heart failure
- Pleural pathologies
Unusual causes of cough: In patients with chronic cough in which the cause cannot be identified, infrequent or rare etiologies should be considered, such as:
- Zenker's diverticulum
- Proteinosis alveolar
- Extrinsic compression of the tracheobronchial tree: endothoracic goiter, aortic aneurysm.
- Foreign body aspiration (common in young children)
- Lung sequestration.
Anamnesis and physical examination of the cough patient
Key aspects of evaluating a cough patient include a comprehensive medical history, an appropriate physical examination, and a series of complementary tests appropriate to the clinical findings.
Anamnesis: The medical history should include:
- The duration in time of the symptom to be able to frame the cough as acute or chronic (according to this the causes differ).
- The association or not with fever (and its characteristics) and other constitutional symptoms such as weight loss or hyporexia in the case of pulmonary TB, neoplasms or systemic diseases with pulmonary manifestations.
- Coexistence or not with hemoptysis that leads to thinking of pulmonary TB, neoplastic processes, or bronchiectasis as the most frequent causes.
- Notion of epidemiological focus of contact with TB patients.
- Questioning about smoking: Nicotinic addiction is the main risk factor for the development of COPD and lung cancer. It is important to remember that "Every patient who smokes, over the age of 40, with a change in their habitual cough rhythm, should be suspicious of lung cancer."
- Inquire about changes in the voice suggestive of laryngeal involvement.
- Find out the existence of "throat throat", sensation of mucus in the pharynx, postnasal drip, recurrent nasal congestion, night snoring, history of sinusopathies or nasofacial trauma to find out the most frequent cause of chronic cough that is chronic postnasal drip.
- Recent history of allergic rhinitis or asthma with or without perception of nocturnal or daytime wheezing (2nd cause of chronic cough)
- Coexistence of cough with digestive symptoms such as heartburn, heartburn or retrosternal burning in the case of gastroesophageal reflux (a frequent cause of chronic cough).
- Treatment with drugs that inhibit the angiotensin-converting enzyme (ACEI) or other drugs with potential lung toxicity (amiodarone, methototexate, antineoplastic drugs, etc.).
- History of heart disease with left ventricular failure.
- Neoplastic or systemic disease history with potential lung involvement (rheumatologic or autoimmune diseases).
- Question whether or not the cough is accompanied by expectoration and its characteristics, if any. COPD, bronchiectasis, tumors, pulmonary TB usually occur with productive cough. They usually present non-productive cough, postnasal drip, GE reflux, cough due to ACE inhibitors, chronic interstitial lung diseases, and psychogenic cough. Bronchial asthma and congestive heart failure can occur with or without expectoration.
- Investigate the presence or absence of associated risk factors: homosexuality, addiction to inhaled or intravenous drugs, recent immobilization or prolonged rest, trips of more than 8 hours by plane in recent times (these last 2 factors predispose to pulmonary thromboembolism), exposure environmental or professional to toxic, fumes, gases or dust.
- In addition to all these data from the interrogation of cough, the pattern of occurrence during the day can in some circumstances lead to thinking about some etiologies: cough in the morning: it is associated with bronchiectasis (due to the accumulation of secretions during the night), allergies such as allergic rhinitis that worsens in the early morning hours and is often associated with morning cough; cough at night: may be due to asthma or congestive heart failure (CHF). Postnasal drip and gastroesophageal reflux are also frequent causes of predominantly nocturnal cough.
- Psychogenic cough improves during sleep and worsens in the morning upon waking;
- Cough when eating food: suggests esophageal diverticulum, tracheoesophageal fistula, or bronchial aspiration due to swallowing disorder (especially in elderly people or people with paresis of the soft palate as a consequence of strokes).
The physical examination will attempt to search for target data. If it is possible to "hear" the cough and, if there is sputum, visualize it and analyze its characteristics. The physical exam focuses on certain key areas: the head and neck, the chest and the cardiovascular system. The presence of dark colorations around the eyes caused by vasodilation in allergic patients is investigated. Pale congestion of the nasal mucosa and rhinorrhea, sometimes accompanied by tearing and conjunctival injection, may indicate allergic rhinitis. A cobblestone appearance of the mucosa in the posterior pharynx often accompanies postnasal drip or allergic rhinitis. The characteristics of the pharyngeal tonsils are observed, generally hypertrophic in mouth respirators.
Sensitivity to percussion on the maxillary or frontal sinuses, especially if accompanied by discharge of nasal mucus for more than 7 to 10 days, may be consistent with sinusitis.
If the history suggests it, the nasal examination should be valued, in search of nasal polyps, turbinate hypertrophy, alterations in the septum, etc; of the larynx, in case of persistent or recurrent dysphonia to rule out different laryngeal processes and of the external auditory canals in the event that the symptoms lead to think about pathology at that level.
It is important to perform a systematic palpation of the neck in search of cervical or supraclavicular lymphadenopathy or abnormalities in thyroid semiology in the anterior neck region.
Examine the anteroposterior thoracic diameter to investigate hyperinflation suggestive of air trapping characteristic of chronic respiratory diseases such as chronic bronchitis and COPD. Unilateral dullness may suggest a bronchial obstruction of a different nature that causes partial or total pulmonary atelectasis if accompanied by a decrease or abolition of the vesicular murmur. Sometimes the presence of a dullness that displaces and disappears with the lateral decubitus (sign of the positive unevenness) may suggest pleural effusion.
The patient should be auscultated during normal ventilation and during forced expiration. This last maneuver is vital and often reveals wheezing that is not detected during normal ventilation; These wheezes can make you suspect asthma. A stridor or strong central wheezing may suggest a mass in the lumen of the trachea or in the carinal region due to different pathologies that compromise the central zone of the airway.
The presence of fixed crepitant and sub-crepitant rales in a lung base or in both bases can be detected in the patient with bronchiectasis even outside the process of exacerbation of the same. The presence of bibasal crepitant rales may be suggestive, in a given clinical context, of interstitial lung disease or CHF.
Do not forget that the existence of acropachy can guide certain pathologies such as cystic fibrosis in boys, bronchiectasis, and even bronchogenic carcinoma, in the latter case as a paraneoplastic manifestation.
Special attention should be paid to the cardiological examination trying to demonstrate alterations in the heart rhythm, murmurs, 3rd or 4th heart sounds, jugular engorgement, malleolar edema.
Finally, if the anamnesis and the physical examination fail to establish the cause of the cough, a frequent situation in cases of chronic cough, it is necessary to resort to a series of complementary diagnostic studies that, in order to follow an ordered sequential path, must resort to the algorithm. diagnosis of persistent or recurrent chronic cough.
Among the etiologies of chronic cough, the most frequent are chronic smoker's bronchitis, chronic post-nasal drip syndrome (GRN), asthma, gastroesophageal reflux (GER), ACEI drugs, pleuropulmonary diseases (infectious, neoplastic, interstitial and autoimmune) and psychogenic cough.
After an exhaustive interrogation and a thorough physical examination, the first study that is required in the evaluation of a cough that becomes chronic over time is the request for a chest x-ray and profile that is essential for the diagnosis of pulmonary pathology. such as TB, bronchogenic carcinoma or interstitial lung diseases and, if it were suggestive of these pathologies, these etiologies need more complex complementary studies for confirmation.
Starting from a normal chest radiograph, ruling out smoker's chronic bronchitis and excluding patients receiving ACE inhibitors, retronasal drip (NRG), asthma, and gastroesophageal reflux account for 95% of the causes of chronic cough.
In practice, in conjunction with chest radiography, a facial sinus radiograph is requested to evaluate for NRG, the leading cause of chronic cough in all series of studies.
At this point, if a definitive diagnosis is already obtained or strongly suspected, its specific treatment will begin: cessation of smoking in the smoker; suppression of drugs in the case that the patient is taking ACE inhibitors or others with a potential pulmonary toxic effect (the diagnosis is assumed if the cough disappears or improves); treatment with a more oral nasal decongestant antihistamine for 7 to 10 days, adding if necessary nasal corticosteroids, if post-nasal drip syndrome is suspected; if the picture was clearly due to asthma due to a previous history or due to the typical physical examination finding of wheezing suggestive of the diagnosis, inhaled steroids are indicated to control allergic bronchial inflammation;
If, after these diagnostic procedures, the aetiology of the cough is clear, laboratory tests should be requested to assess the presence of eosinophilia in the CBC and to assess atopy through IgE dosing for the purposes of investigating allergy. In conjunction with this, spirometry with a bronchodilator test should be performed. Spirometry can demonstrate an obstructive pattern that leads to asthma, COPD, or other lung pathologies. In the event of obstruction, a bronchodilator test is performed since the demonstration of an increase of 12% or more in FEV1 after it or normalization of spirometry will indicate reversibility of the obstruction to airflow suggestive of asthma. If after these studies the cause of the cough is still not clear, The next step will be to perform a provocation test or bronchial hyperreactivity test given the high frequency of asthma as a cause of chronic cough (2nd cause after GRN), since it can present as an asthmatic equivalent. The test is considered positive when FEV1 decreases 20% of the initial value after inhalation of the substance used for the challenge test. This test has no false negatives. If the test is positive, treatment with inhaled corticosteroids will be started; If, despite this treatment, the cough persists, the study of the cough will continue, since it is assumed that the cough is caused by more than one cause. The test is considered positive when FEV1 decreases 20% of the initial value after inhalation of the substance used for the challenge test. This test has no false negatives. If the test is positive, treatment with inhaled corticosteroids will be started; If, despite this treatment, the cough persists, the study of the cough will continue, since it is assumed that the cough is caused by more than one cause. The test is considered positive when FEV1 decreases 20% of the initial value after inhalation of the substance used for the challenge test. This test has no false negatives. If the test is positive, treatment with inhaled corticosteroids will be started; If, despite this treatment, the cough persists, the study of the cough will continue, since it is assumed that the cough is caused by more than one cause.
The next step is the confirmation of the GOR through gastroenterological studies that will be evaluated individually (contrasted esophagogastric Rx, videoesophagogastrofibroscopy and 24-hour pH-metry). PH-metry is the diagnostic test with the highest sensitivity and specificity to establish the diagnosis of GER. If the test is diagnostic, specific treatment is started.
The last diagnostic step, and only in special cases after an individual assessment, is the performance of a bronchofibroscopy and / or CT of the chest (the latter, for example, in the investigation of bronchiectasis or of lung or mediastinal lesions that are not clearly visible on the X-ray). chest). If the chest X-ray is normal, bronchofibroscopy is generally uneconomical to establish the causal diagnosis of cough. This could have been indicated initially for other reasons such as an alteration in the chest X-ray, due to hemoptysis or suspicion of a foreign body.
Sometimes, after completing the entire study, a final diagnosis cannot be reached. At this time and as a diagnosis of exclusion, psychogenic cough will be taken into account, especially in adolescents and in patients with emotional problems; in these cases, a psychological evaluation and eventual psychiatric treatment will be required.
When despite the complete study the cause of the cough is not found or it does not disappear with the previous treatment, it is indicated to initiate a symptomatic treatment that is aimed at eliminating the cough reflex. It would also be indicated at any level of the protocol, if cough complications can pose a danger to the patient (for example, rib fractures in a patient with osteoporosis), or when the known cause does not have definitive treatment, such as lymphangitis carcinomatous.