What are the differential diagnoses for a patient with a persistent cough, postnasal drainage, and a history of severe allergies?

Differential Diagnoses for Persistent Cough with Postnasal Drainage and Severe Allergies

Primary Differential Diagnoses

The differential diagnosis for this patient includes Upper Airway Cough Syndrome (UACS) secondary to allergic rhinitis, perennial nonallergic rhinitis, postinfectious rhinitis, vasomotor rhinitis, bacterial sinusitis, and gastroesophageal reflux disease (GERD). 1

Upper Airway Cough Syndrome (UACS) - Most Likely

• UACS is the most common cause of chronic cough in adults and should be at the top of this differential. 1, 2
• The patient's persistent cough, postnasal drainage, and resolved sore throat are classic features of UACS. 1
• Notably, approximately 20% of patients have "silent" UACS without obvious postnasal drip symptoms yet still respond to treatment, so absence of visible drainage does not exclude this diagnosis. 1, 2
• The cobblestoning appearance of the oropharyngeal mucosa, if present on examination, would further support this diagnosis. 2

Allergic Rhinitis - Primary Underlying Etiology

• Given the patient's history of severe allergies worsening with seasonal changes and mold exposure, allergic rhinitis is highly likely driving the UACS. 1
• Allergic rhinitis affects up to 20% of individuals and is an IgE-mediated hypersecretory state. 1
• The patient's symptoms worsening with seasonal changes and mold exposure strongly suggest perennial allergic rhinitis with seasonal exacerbations. 1
• Indoor allergens such as mold, dust mites, and animal danders are commonly associated with perennial allergic rhinitis. 1

Perennial Nonallergic Rhinitis (Including Vasomotor Rhinitis)

• This includes vasomotor rhinitis and nonallergic rhinitis with eosinophilia (NARES), both diagnoses of exclusion. 1
• Vasomotor rhinitis presents with excessive watery secretions triggered by odors, temperature changes, or humidity changes, related to autonomic imbalance. 1
• NARES presents similarly to vasomotor rhinitis but includes nasal and ocular pruritus with eosinophils in nasal secretions despite negative allergy testing. 1
• These are less likely given the patient's documented severe allergies and clear seasonal/mold triggers. 1

Postinfectious Rhinitis/Upper Respiratory Infection

• The nearly one-week duration of symptoms following what appears to be a viral URI makes postinfectious rhinitis a strong consideration. 1
• Postinfectious cough can persist for weeks after the initial infection resolves. 2
• The resolved sore throat suggests the acute infectious phase has passed, but postinfectious inflammation continues. 1

Bacterial Sinusitis

• Should be considered if symptoms persist beyond 10-14 days or if sudden worsening occurs with facial/dental pain. 1
• The absence of fever and clear lung sounds make acute bacterial sinusitis less likely at this presentation. 1
• Mucosal thickening <8mm on imaging is associated with sterile cultures in 100% of cases, so imaging findings must be interpreted cautiously. 2

Gastroesophageal Reflux Disease (GERD)

• GERD frequently mimics UACS because it causes upper respiratory symptoms and can present with chronic cough and postnasal drip sensation. 1
• If symptoms fail to respond to upper airway treatment within 2 weeks, GERD should be strongly considered. 2
• GERD can coexist with UACS, making sequential or simultaneous treatment necessary in some cases. 2

Less Likely but Important Differentials

Rhinitis Due to Anatomic Abnormalities

• Includes septal deviation, nasal polyps, or turbinate hypertrophy causing mechanical obstruction. 1
• Less likely given no mention of chronic nasal obstruction or previous structural issues. 1

Rhinitis Medicamentosa

• Caused by overuse of topical decongestant sprays (rebound congestion). 1
• The patient is not currently using nasal sprays, making this unlikely. 1

Occupational or Irritant-Induced Rhinitis

• Exposure to physical or chemical irritants in the workplace or environment. 1
• Should be explored if environmental history reveals relevant exposures. 1

Critical Clinical Pitfalls to Avoid

• Do not dismiss the diagnosis of UACS simply because the patient lacks visible postnasal drainage or typical symptoms—"silent" UACS is common. 1, 2
• Failure to give an empiric trial of first-generation antihistamine/decongestant therapy before pursuing less common diagnoses is a major diagnostic pitfall. 1
• Newer-generation antihistamines like Zyrtec (cetirizine) are less effective for nonallergic causes of UACS compared to first-generation agents due to lack of anticholinergic properties. 2, 3
• The patient's concern about nosebleeds from nasal sprays can be mitigated by proper technique—spraying away from the nasal septum toward the lateral nasal wall. 2
• GERD can masquerade as UACS, so if upper airway treatment fails after 2 weeks, empiric proton pump inhibitor therapy for 8-12 weeks should be initiated. 2, 4