Why Your Cough Won't Stop - Differential Diagnosis and Management of Cough Lasting 3+ Weeks

Definition and Epidemiology of Chronic Cough

Cough is classified by duration: acute cough (less than 3 weeks), subacute cough (3-8 weeks), and chronic cough (8 weeks or more). Many acute coughs are caused by infections such as colds or influenza and resolve on their own. However, cough persisting beyond 3 weeks requires consideration of non-infectious causes.

Chronic cough is considered common in adults, and its impact on quality of life is not small. Sleep disruption from coughing, conversation interruption, stress urinary incontinence, rib fractures (from severe coughing), and social embarrassment create cumulative physical and psychological burden. Women have higher cough reflex sensitivity than men and tend to have higher chronic cough prevalence.

Cough-Variant Asthma - The Most Common Cause of Chronic Cough

Cough-variant asthma is a form of asthma where cough is the only main symptom, without wheezing or breathing difficulty. In Japan, it is considered a common cause of chronic cough. Chronic airway inflammation and heightened hypersensitivity are the underlying factors, with cough triggered by cold air, exercise, perfume, cigarette smoke, and house dust.

Characteristic features include cough worsening from nighttime to early morning, exacerbation during seasonal transitions, and cough relief with bronchodilator (beta-2 agonist) inhalation. Diagnosis involves exhaled nitric oxide (FeNO) measurement, airway hyperresponsiveness testing, and response to bronchodilators. First-line treatment is inhaled corticosteroids, and it can take several weeks for effects to appear. For the relationship between allergies and cough, see our article on seasonal allergy lifestyle management.

Post-Nasal Drip Syndrome (Upper Airway Cough Syndrome)

Post-nasal drip is a condition where nasal secretions flow down the back of the throat. These secretions are thought to irritate the pharynx and larynx, causing chronic cough. Allergic rhinitis, chronic sinusitis, and vasomotor rhinitis are common causes. Post-nasal drip is also one of the main causes of chronic cough.

Characteristic symptoms include the sensation of something dripping down the back of the throat, frequent throat clearing, phlegmy cough upon waking, and concurrent nasal congestion or runny nose. Treatment depends on the underlying cause and may include antihistamines, nasal corticosteroid sprays, antibiotics (for bacterial sinusitis), and nasal irrigation (saline nasal rinse).

Gastroesophageal Reflux Disease (GERD) Cough

Stomach acid refluxing up the esophagus and reaching the pharynx or trachea in small amounts can trigger the cough reflex. GERD-related cough is another cause of chronic cough, and "silent GERD" without typical reflux symptoms like heartburn is not uncommon. Suspect GERD if cough worsens after meals or at bedtime, voice becomes hoarse, or there is a sensation of something in the throat.

Diagnosis is often made by whether cough improves with a trial of proton pump inhibitors (PPIs) for 2-3 months. Lifestyle modifications include avoiding food 3 hours before bedtime, elevating the upper body 15-20cm during sleep, and reducing fatty foods, caffeine, alcohol, and carbonated beverages. For detailed acid reflux management, see our article on acid reflux lifestyle management.

Drug-Induced Cough and Post-Infectious Cough

ACE inhibitors (enalapril, lisinopril, etc.) are widely used as antihypertensives, but a dry cough has been reported as a side effect in 5-35% of users (American College of Chest Physicians guideline, 2006). The heightened airway cough reflex is thought to involve ACE inhibitors suppressing bradykinin degradation. It can appear within hours to months after starting the medication and usually resolves 1-4 weeks after discontinuation, though it may linger for up to 3 months.

Post-infectious cough is a condition where cough persists for 3-8 weeks after a cold or influenza. The cause is considered to be temporarily heightened cough reflex sensitivity due to airway mucosal damage from infection. It usually resolves naturally, but if it persists beyond 8 weeks, other causes should be investigated.

When to See a Doctor and What Tests to Expect

See a healthcare provider if: cough has lasted more than 3 weeks, there is blood in sputum, weight loss is occurring, night sweats are present, breathlessness is worsening, or you have a smoking history (lung cancer risk). A pulmonologist is ideal, but a general internist can also help initially.

Testing proceeds stepwise. First, chest X-ray rules out pneumonia, tuberculosis, and lung cancer. Next, pulmonary function testing (spirometry) evaluates asthma and COPD. FeNO measurement indicates eosinophilic airway inflammation (cough-variant asthma). If diagnosis remains unclear, chest CT, bronchoscopy, and 24-hour esophageal pH monitoring may be added.

Atopic Cough and Eosinophilic Bronchitis

Atopic cough is a condition where eosinophilic airway inflammation causes persistent cough, but unlike cough-variant asthma, there is no airway hyperresponsiveness. It is common in people with atopic predisposition (allergic constitution), characterized by dry cough with throat irritation. Antihistamines and inhaled corticosteroids are used. Eosinophilic bronchitis similarly involves eosinophilic inflammation but is diagnosed by elevated sputum eosinophils. Differentiating these conditions from cough-variant asthma is important, as they are distinguished by differences in treatment response.

Home Remedies for Cough Relief

Alongside medical consultation, incorporate home measures. Humidification prevents airway mucosal drying and helps reduce cough. Maintain indoor humidity at 50-60% and use a humidifier at bedtime. Honey (1-2 teaspoons) has been shown in multiple clinical trials to be as effective as or superior to cough suppressants (contraindicated under age 1).

Warm beverages (honey lemon, ginger tea) moisten the throat and can help temporarily suppress the cough reflex. Elevating the upper body slightly during sleep tends to reduce cough from post-nasal drip or acid reflux. For smokers, quitting is the basic measure. Avoid secondhand smoke as well. Since stress can worsen cough, understanding how chronic stress affects the body and working on stress management is also important.

Prolonged coughing depletes energy and accumulates sleep disruption and social interference. Do not dismiss it as "just a cough" - always see a doctor if it persists beyond 3 weeks. Once the cause is identified, most chronic coughs can be expected to improve with appropriate treatment. Multiple overlapping causes are not uncommon, so if one treatment does not help, continue investigating other causes.