What are the appropriate management and treatment options for a patient presenting with a dry cough, considering potential underlying conditions such as allergies, asthma, or chronic respiratory diseases?

Management of Dry Cough

For dry cough, begin with a first-generation oral antihistamine/decongestant combination as initial empiric treatment, targeting upper airway cough syndrome (UACS) as the most common cause, then proceed systematically through asthma and gastroesophageal reflux if cough persists. 1, 2

Initial Classification and Red Flag Assessment

• Classify cough by duration: acute (<3 weeks), subacute (3-8 weeks), or chronic (>8 weeks), as this determines the entire management pathway 3, 2
• Immediately discontinue ACE inhibitors if the patient is taking them, as this is a common reversible cause 1, 2
• Rule out life-threatening conditions such as pneumonia or pulmonary embolism before proceeding with algorithmic management of benign causes 1, 2
• Obtain chest radiography in all patients with chronic cough and those with acute cough showing atypical symptoms 1
• Perform spirometry in all patients with chronic cough to identify airflow obstruction 1

Systematic Treatment Algorithm for Chronic Dry Cough

The key principle is sequential and additive therapy because multiple causes frequently coexist 1, 2

Step 1: Treat Upper Airway Cough Syndrome (UACS) First

• Start with a first-generation oral antihistamine/decongestant combination as initial empiric treatment 1, 2, 4
• This targets post-nasal drip and rhinosinusitis, which are among the most common causes of chronic dry cough 5

Step 2: Evaluate and Treat Asthma Next

• If cough persists after UACS treatment, work up asthma as the next cause 1, 2
• Medical history is unreliable for ruling asthma in or out—spirometry or bronchoprovocation challenge must be performed 1
• If spirometry shows reversible airflow obstruction, treat with combination therapy of inhaled corticosteroids, inhaled β-agonists, or oral leukotriene inhibitors 1
• If bronchoprovocation challenge is unavailable, administer an empiric trial of anti-asthma therapy 1, 4

Step 3: Consider Non-Asthmatic Eosinophilic Bronchitis (NAEB)

• If UACS and asthma have been treated without eliminating cough, evaluate for NAEB with induced sputum testing for eosinophils 1, 2
• If induced sputum testing cannot be performed, give an empiric trial of corticosteroids 1
• Patients with normal spirometry and bronchodilator response suspected of having cough-predominant asthma or eosinophilic bronchitis should receive a therapeutic trial of prednisolone 1

Step 4: Treat Gastroesophageal Reflux Disease (GERD)

• If cough responds only partially or not at all to interventions for UACS and asthma/NAEB, institute treatment for GERD 1, 2
• GERD is frequently overlooked as an extrapulmonary cause of chronic cough 1

Symptomatic Antitussive Therapy

When disease-specific treatment fails or for symptomatic relief:

• Use dextromethorphan 30-60 mg for short-term use only, as the standard OTC dose is subtherapeutic and maximum cough reflex suppression occurs at 60 mg 3
• Do not prescribe codeine or codeine-containing products, as they have no greater efficacy than dextromethorphan but significantly more adverse effects 3
• The FDA label for dextromethorphan warns against use in chronic cough that occurs with smoking, asthma, or emphysema, or cough with excessive phlegm 6
• For idiopathic chronic cough (diagnosis of exclusion only), treatment options include dextromethorphan, baclofen, nebulized local anesthetics, and low-dose morphine 1, 2

Special Considerations and Contraindications

• Cough suppression is relatively contraindicated in pneumonia and bronchiectasis where cough clearance is important 1, 2
• In patients with interstitial lung disease, evaluate for asthma, UACS, or GERD before attributing cough to the lung disease itself 7
• Predominantly middle-aged women with idiopathic cough often present with long-standing chronic dry cough starting around menopause, with evidence of heightened cough reflex and lymphocytic airway inflammation 1

Common Pitfalls to Avoid

• Do not rely on cough characteristics (timing, quality) for diagnosis—they have minimal diagnostic value 2
• Do not treat only one cause—therapy must be given in sequential and additive steps as multiple etiologies frequently coexist 1, 2
• Do not diagnose idiopathic cough prematurely—ensure thorough evaluation and treatment trials of UACS, asthma, NAEB, and GERD first 1, 2
• Do not prescribe antibiotics reflexively for viral causes, as this contributes to antimicrobial resistance 3, 2
• Do not use subtherapeutic doses of dextromethorphan—60 mg is required for maximum effect 3

When to Refer

• Refer to a cough specialist if cough remains undiagnosed after all sequential treatments have been attempted and uncommon causes have been ruled out 1, 2
• Consider high-resolution CT scan and bronchoscopy if cough persists despite appropriate sequential treatment or if red flag symptoms are present 2