A cough is a sudden, often repetitive, spasmodic contraction of the thoracic cavity, resulting in a violent release of air from the lungs, and usually accompanied by a distinctive sound. A cough by itself is not a complete diagnosis but rather a symptom of an underlying condition, despite this, it accounts for one of the most common indications for visits to the general practitioners and family physicians with a good proportion of these cases resulting in a pulmonology referral.

Coughing is an action the body takes to get rid of substances that are irritating the air passages. The act of coughing can be triggered by a myriad of conditions physiologic and otherwise, A cough is mostly initiated to clear a buildup of phlegm within the trachea. Coughing can also be triggered by a bolus of food entering the trachea and other parts of the respiratory tree rather than the esophagus due to a failure of the epiglottis. During the management of cough the duration is an important tool utilized by the clinicians; and when presented with a history of frequent or chronic coughing the presence of an underlying disease should be suspected. In non-smoking patients with a normal chest X-ray, chronic cough in 93% of these patients’ cohort can be attributed to asthma, heartburn or post-nasal drip. Other causes of chronic cough include chronic bronchitis and medications such as ACE inhibitors. Coughing can happen voluntarily as well as involuntarily.

The uncleanness of most cases of cough with regard to etiology, duration, and other precipitating symptoms coupled with the lack of a universal guideline for quantifying cough results in variability during its assessment. Thus, a thorough evaluation should be done to isolate the etiology of the patient’s cough when they present, and before initiating therapy for symptomatic relief.

The accepted classification of cough is that of the ACCP(American college of chest physicians).Cough is classified into 3 types depending on its duration.

• Acute cough: last less than 3 weeks
• Sub-acute cough: last between 3 and 8 weeks.
• Chronic cough: last longer than 8 weeks.

The act of coughing is a vital one that leads to the mucociliary clearance of excess secretions from the airway and other parts of the respiratory tree.Cough occurs via a complex neurophysiologic cough reflex arc.

There are various causes of cough,the most common causes are:

• Allergic Rhinitis
• Asthma
• Bronchiectasis
• Gastroesophageal Reflux Disease (GERD)
• Post-nasal drip

Cough causes can also be classified according to the organ system, see the segment on cough causes for details.

Making a differential diagnosis when a patient presents with a cough can be challenging however when the clinician asks about the other associated symptoms such as fever, vomiting, night sweats, weight loss, sputum production, and quantity, smoking history, drug use and most importantly the duration of the cough, making a differential diagnosis becomes less challenging.See the segment on Cough differential diagnosis for an extensive overview of the various differential diagnosis of cough.

Cough is a protective reflex, however, some factors can increase one’s risk of having a cough.

• Allergies.
• Smoking.
• Air pollution due to aerosolized chemicals, dust, smoke, etc.
• Uncontrolled Bronchial asthma & other chronic diseases.

The various complications associated with cough can be categorized according to systems involved also, Cough complications can also be acute or chronic. See the segment on Cough natural history, complications, and prognosis.

There is no single diagnostic study of choice for the diagnosis of cough.

A detailed cough history should cover the following:

• Onset of symptoms.
• Dry vs Productive cough.If productive, sputum content, color, amount, etc.
• Duration.
• Exacerbating/relieving factors.
• Previous episodes.
• Frequency.
• Drug use eg:ACEIs

• Fever.
• Chills and Rigor.
• Weight loss.
• wheezing.
• Associated hemoptysis
• Post nasal dripping
• Allergy history
• Smoking history
• Environmental or Occupational exposure to air pollutants.

Once an in-depth history is taken from the patient, a detailed physical examination consisting of inspection, palpation, percussion, and auscultation should be done when evaluating coughing patients.

Some laboratory test used when evaluating cough are:

• Complete blood count
• CRP
• Nasopharyngeal swab
• Sputum analysis & culture

Chest X-rays are a go-to investigative tool used by most clinicians when evaluating cough. Despite the routine use of CXR when evaluating cough, the most common causes of cough in the general population such as Gerd, Asthma and Post nasal drip cannot readily be diagnosed by CXR.

The use of a high resolution CT may identify pulmonary parenchymal lesions/diseases that were not readily picked up by CXR in patients with chronic cough.

The use of MRI in the diagnosis of cough is particularly useful when red flags are noted during the detailed medical history and physical examination of the patient.

• Bronchoscopy.
• Sinus imaging.

Treatment of cough depends on its etiology. Cough treatment is mostly medical with the use of cough syrups, antibiotics, modifying lifestyle, etc. The use of surgery limited to few cases refractory to medical therapy. See the chapter on Cough medical therapy and Cough surgery for a detailed algorithm on cough treatment.

Avoiding smoking, areas with air pollution, and proper hand hygienic practices can prevent one from acquiring cough due to other causes.

There are no established guidelines for the secondary prevention of cough.

The accurate classification of cough is the first step to accurately diagnosing it. in 1998 the American college of chest physicians (CHEST), Expert cough panel postulated that cough should be classified based on its duration. Prior to this, a detailed patient history about the character, timing, sputum production, etc was utilized when evaluating cough; however, the panel found out that these parameters are not sufficient in establishing a definite etiology of cough.

The first expert panel in 1998 had initially classified cough as acute cough( ie lasting < 3 weeks) and chronic cough (ie, lasting 3-8 weeks) but the second American college of chest physicians ACCP panel in 2006 reclassified cough into 3 categories based on its duration as listed below.

Cough may be classified into 3 groups:^[1]

• Acute coughs last less than 3 weeks.
• Subacute coughs last between 3 and 8 weeks.
• Chronic coughs last longer than 8 weeks.

2006 ACCP Cough Panel classification based on duration.^[2]

There is limited information about the historical perspective of cough.

There is limited information about the historical perspective of cough.

The act of coughing is a vital one that leads to the mucociliary clearance of excess secretions from the airway and other parts of the respiratory tree.Cough occurs via a complex neurophysiologic cough reflex arc.

The cough reflex is constituted by three main components ie

• The Afferent pathway: This is made up of sensory nerve fibers of the ciliated epithelium found in the upper airways. The afferent impulses are transmitted into the medulla.

• Central pathway: This is a central area located within the pons and brainstem. It coordinates the cough reflex arc.^[1]

• The efferent pathway: cough impulses that are originated from the cough central travels via the vagus nerve,phrenic nerve, and spinal motor nerves to the diaphragm and abdominal wall muscles.

There are 3 major classes of afferent sensory nerves,this classification is based on there conduction velocity(A-fiber, > 3 m/s; C-fiber, < 2 m/s),origin ,myelination,neurochemistry etc.

• Rapidly adapting receptors (RARs)
• Slowly adapting stretch receptors (SARs)
• C-fibres.

For an effective cough to be produced, a sequence of timed mechanical events divided into 3 phases has to take place.^[2]

• The inspiratory phase: Here, there is inhalation of an appropriate amount of gas, the amount of gas inhaled tends to vary from 50% of the tidal volume to about 50% of the vital capacity.^{[3] [4]}The inspiratory phase also bring about a structural change in the architecture of the expiratory muscles ie lenghtning and strentning of the expiratory muscles thus leading to the a generation of the required amount of intrathoracic pressure.
• The Compression Phase: The contraction of the muscles of the chest wall, abdominal wall, and the diaphragm against a closed glottis brings about a rapid increase in intrathoracic pressure.The pressure developed in the glotts during this compression phase could be as high as 300mmhg.^[5]
• The Expiratory Phase: At this last phase, the glottis is open and the large intrathoracic pressure that was developed in the compressive phase brings about a large expiratory airflow and the unique sound associated with coughing.^[5]

The ability to cough efficiently and effectively cannot be overstated and when patients have impaired ability to cough, they are at an increased risk of atelectasis, pneumonia, and other chronic airways diseases secondary to aspiration and retention of secretions. In patients with chest wall deformities, abdominal wall deformities and other neuromuscular disorders may have problems generating the required flow pressure needed to clear respiratory secretions effectively.^[6][7]

This is a very rare nerve disorder associated with chronic cough, in patients with this disorder, the stimulation of the external auditory meatus leads to the activation of the auricular branch of the vagus nerve(Arnold’s nerve) thus stimulating the cough reflex. Treatment of patients with this condition and other sensory vagal neuropathy with chronic coughis with gabapentin.^[8]

Coughing during an injection can lessen the pain of the needle stick caused by a sudden, temporary rise in pressure in the chest and spinal canal, inhibiting the pain-conducting structures of the spinal cord.^[9]

A cough is a protective reflex that helps clear secretions and foreign material from the airways. In adults, cough is commonly classified by duration as acute (less than 3 weeks), subacute (3 to 8 weeks), and chronic (more than 8 weeks).^[1]

A persistent cough can be debilitating, socially distressing, and adversely impair quality of life(Qol). One of the more common presentations to a medical practitioner is a dry cough. The common causes of chronic dry coughing include post-nasal drip, gastroesophageal reflux disease, asthma, post viral cough and certain drugs such as beta blockers, ACE inhibitors and aspirin. If a cough lasts for more than three weeks, multiple causes are likely and symptoms will abate only when all the causes are treated will the patient be symptom-free. Individuals who smoke often have a smoker’s cough, a loud, hacking cough which often results in the expiration of phlegm.

Coughing may also be used for psychological or social reasons, such as the coughing before giving a speech. This is known as psychogenic, habit or tic coughing, and may increase in frequency in social situations featuring conflict.

Given its irritant nature to mammal tissues, capsaicin is widely used to determine the cough threshold and as a tussive stimulant in clinical research of cough suppressants.^[2][3]

• Allergic Rhinitis
• Asthma
• Bronchiectasis
• Gastroesophageal Reflux Disease (GERD)
• Post-nasal drip

Chronic cough often has more than one contributing cause, and symptoms may not resolve until all contributing conditions are addressed.^[1]

Common or important causes to consider in adults with chronic cough include:

• **Upper airway cough syndrome** (often related to rhinitis or sinus disease)

• Upper airway symptoms may be minimal or absent. Consider allergic rhinitis, nonallergic rhinitis, and chronic rhinosinusitis. First generation antihistamines with anticholinergic effects and intranasal therapies are often used as initial management in appropriate clinical contexts.^[1]

• **Asthma and cough variant asthma**

• Cough can be the predominant symptom. Bronchoprovocation testing may support the diagnosis, but response to anti inflammatory therapy is also important clinically.^[1]

• **Nonasthmatic eosinophilic bronchitis**

• Presents with chronic cough and airway eosinophilia without variable airflow obstruction. It may respond to inhaled glucocorticoids. Fractional exhaled nitric oxide or induced sputum (when available) can support the diagnosis in the right setting.^[1]

• **Gastroesophageal reflux and reflux related cough**

• Reflux can contribute even without classic reflux symptoms. Acid suppression alone may be insufficient, and non acid reflux may play a role. Improvement can require an adequate therapeutic trial, and cough may take weeks to months to abate after effective control of contributing reflux mechanisms.^[1]

• **Medication related cough**

• ACE inhibitor cough is a classic cause. Medication reconciliation is essential, especially when cough began after a new medication was started or intensified.^[1]

• **Smoking related disease and chronic airway disease**

• Smoking can cause chronic bronchitis and contribute to cough. Evaluate for Chronic Obstructive Pulmonary Disease and other smoking related airway disease based on history and spirometry findings.^[1]

• **Interstitial lung disease**

• Consider when there is dyspnea, crackles, abnormal imaging, or systemic features. Importantly, common non ILD causes of cough can coexist in patients with ILD, so the presence of ILD does not exclude other treatable contributors.^[1]

• **Airway lesions and less common structural disease**

• Tracheobronchial disease, bronchial obstruction, or aspirated foreign body should be considered when there are focal findings, recurrent pneumonia, hemoptysis, or unexplained symptoms. Bronchoscopy may be considered in selected patients, including those with persistent cough despite guideline based evaluation and management, even when imaging is not clearly diagnostic.^[1]

After evaluation and appropriate treatment trials for common and relevant causes, some patients have persistent cough that is either:

• **Refractory chronic cough**: cough persists despite treatment of identified causes
• **Unexplained chronic cough**: no cause is identified after a systematic evaluation

A key concept is **cough hypersensitivity**, in which cough reflex pathways are overly sensitive and cough can be triggered by low level mechanical, chemical, or thermal stimuli. Patients may report throat tickle, laryngeal paresthesia, or cough triggered by talking, odors, cold air, or eating. This diagnosis is typically considered only after other etiologies have been reasonably excluded and treated.^[1]

• Smoker’s cough
• Aspiration
• Congestive heart failure
• Postnasal drip

  • Most common cause of chronic cough in nonsmokers

• GERD

  • Second most common cause of chronic cough in nonsmokers

• Asthma/reactive airway disease
• ACE inhibitor use
• Pneumonia

  • Typical pneumonia is characterized by acute or subacute onset of fever, dyspnea, fatigue, pleuritic chest pain, and cough
  • Atypical pneumoniais characterized by more gradual onset, dry cough,headache, fatigue, and minimal lung signs

• Acute bronchitis

  • Most commonly caused by viruses
  • Postviral bronchitis may last beyond 6 weeks

• Aspirated foreign body
• Lung cancer
• COPD
• Sarcoidosis
• Cryptogenic organizing pneumonia
• Filarial disease

• Postnasal drip
• Tuberculosis
• COPD
• Lung cancer
• Smoker’s cough
• Asthma with secondary infection
• Pneumonia
• Bronchitis

Making a differential diagnosis when a patient presents with a cough can be challenging however when the clinician ask about the other associated symptoms such as fever, vomiting, night sweats, weight loss, sputum production and quantity, smoking history, drug use and most importantly the duration of the cough,making a differential diagnosis becomes less challenging.

For the differential diagnosis of productive cough, click here.
For the differential diagnosis of acute cough, click here.
For the differential diagnosis of chronic cough, click here.
For the differential diagnosis of cough and hemoptysis, click here.
For the differential diagnosis of cough and weight loss, click here.
For the differential diagnosis of cough and fever, click here.
For the differential diagnosis of cough and wheeze, click here.
For the differential diagnosis of cough, fever, and hemoptysis, click here.
For the differential diagnosis of cough, fever, and weight loss, click here.
For the differential diagnosis of cough, hemoptysis, and weight loss, click here.

The incidence/prevalence of cough is approximately 10 % of the adult population worldwide.

The incidence/prevalence of cough is approximately 10 % of the adult population worldwide.

^[1]

Common risk factors in the development of cough include Allergies, Smoking, Air pollution, and Upper respiratory tract infections.

Common risk factors in the development of cough include:

• Upper respiratory tract infections.
• Allergies.
• Smoking.
• Air pollution due to aerosolized chemicals, dust, smoke, etc.
• Uncontrolled Bronchial asthma & other chronic diseases.

^[1]

The mechanics of cough as described under cough pathophysiology demonstrate the role of various body systems and organ in the production of a cough. The various complications associated with cough can be categorized according to systems involved also,Cough complications can also be acute or chronic.

The complications of coughing can be classified as either acute or chronic. Acute complications include cough syncope (fainting spells due to decreased blood flow to the brain when coughs are prolonged and forceful), insomnia, cough-induced vomiting, rupture of blebs causing spontaneous pneumothorax, subconjunctival hemorrhage or “red eye“, coughing defecation and in women with a prolapsed uterus, cough urination. Chronic complications are common and include abdominal or pelvic hernias, fatigue fractures of lower ribs and costochondritis.The table below shows the various complications of cough. ^[1]