What is the most likely diagnosis and recommended next steps for a 41-year-old male with an 18‑day dry cough and sensation of trapped phlegm, hoarseness and metallic taste after burping, partial relief with Gaviscon (sodium alginate, sodium bicarbonide, calcium carbonate) and a 5‑day prednisone course, hyperthyroidism treated with methimazole, and a swollen non‑erythematous left nasal turbinate with normal vital signs?

Most Likely Diagnosis and Management

This is a classic case of post-infectious cough with concurrent upper airway cough syndrome (UACS), and the next step is to initiate inhaled ipratropium bromide as first-line therapy while simultaneously treating the upper airway inflammation with a first-generation antihistamine-decongestant combination plus intranasal corticosteroid. 1

Clinical Reasoning: Timeline-Based Diagnosis

Post-infectious cough is diagnosed when cough persists 3–8 weeks following an acute respiratory infection, which precisely matches this patient's 18-day timeline (dry cough → hoarseness → current productive-sounding cough). 1 The key diagnostic features present here include:

• Initial URI symptoms (dry cough, hoarseness) for 3 days, followed by persistent cough for >7 days 1
• Non-purulent sputum character (no bacterial infection) 1
• No fever, clear lungs except transient sounds that clear with coughing 1
• Otherwise healthy nonsmoker 1

Upper airway involvement is confirmed by the swollen left nasal turbinate and history of metallic taste after burping (suggesting both rhinitis and possible reflux). 1 Approximately 20% of UACS cases present as "silent" postnasal drip with minimal overt symptoms, yet still respond to treatment. 2

Immediate Management Algorithm

First-Line Therapy (Start Today)

1. Inhaled Ipratropium Bromide 1

• Dose: 2–3 puffs (17–34 mcg per puff) four times daily
• This has the strongest evidence for attenuating post-infectious cough 1
• Expected response: 1–2 weeks 1

2. First-Generation Antihistamine-Decongestant Combination 2

• Example: Chlorpheniramine 4 mg + sustained-release pseudoephedrine 120 mg twice daily 2
• Critical: First-generation agents are superior to newer non-sedating antihistamines due to anticholinergic properties 2
• To minimize sedation: start once daily at bedtime for 2–3 days, then advance to twice daily 2
• Expected response for UACS: days to 1–2 weeks 1

3. Intranasal Corticosteroid 2

• Fluticasone propionate 100–200 mcg daily (1–2 sprays per nostril) 2
• Full trial duration: 1 month 2
• Addresses the swollen turbinate and upper airway inflammation 2

Supportive Measures

• Guaifenesin 200–400 mg every 4 hours (up to 6 times daily) for symptomatic relief of phlegm 1
• Honey and lemon for central cough reflex modulation 1
• Adequate hydration, warm facial packs, steamy showers, head-of-bed elevation 1

Critical Management Pitfalls to Avoid

Do NOT prescribe antibiotics. 1 The prior prednisone course was appropriate for laryngitis, but antibiotics are explicitly contraindicated for post-infectious cough because the cause is non-bacterial. 1 Colored phlegm does NOT indicate bacterial infection—most post-viral coughs produce colored sputum. 1

Do NOT jump to oral prednisone. 1 Reserve prednisone 30–40 mg daily for 5–10 days only for severe paroxysms that significantly impair quality of life, and only after ruling out UACS, asthma, and GERD. 1

Monitor for decongestant side effects: The pseudoephedrine component can cause insomnia, jitteriness, tachycardia, and worsening hypertension. 2 Check blood pressure after initiating therapy. 2

Addressing the Gastroesophageal Reflux Component

The metallic taste after burping and occasional epigastric acidity suggest "silent GERD," which frequently presents with cough as the sole respiratory manifestation. 3 However, since the patient has partial relief with Gaviscon, continue this for now. If cough persists beyond 2 weeks despite adequate upper airway treatment, initiate high-dose PPI therapy:

• Omeprazole 40 mg twice daily (before meals) for at least 8 weeks 1
• Add dietary modifications (avoid late meals, elevate head of bed, avoid trigger foods) 1
• Response time: 2 weeks to several months 1

Reassessment Timeline and Red Flags

Follow-up at 2 weeks: 1

• If no improvement → proceed to sinus imaging (CT) to evaluate for chronic sinusitis 3
• If partial improvement → continue all therapies (do not stop partially effective treatments) and add GERD therapy 1

Reclassify as chronic cough if persisting >8 weeks: 1

• Systematic evaluation for asthma (bronchoprovocation testing or empiric inhaled corticosteroid trial) 3
• Consider non-asthmatic eosinophilic bronchitis (induced sputum eosinophil count >3%) 3

Return immediately if: 1

• Fever develops
• Hemoptysis occurs
• Dyspnea worsens
• Symptoms fail to improve within 3–5 days

Special Consideration: Hyperthyroidism

The patient's methimazole therapy is appropriate and should be continued. 4 Thyroid disease can occasionally present with chronic cough as a manifestation, but given the clear post-infectious timeline and upper airway findings, this is not the primary driver here. 3

Why This Approach Works

Chronic cough is frequently multifactorial (93.6% of cases involve UACS, asthma, or GERD alone or in combination). 5 This patient likely has both post-infectious airway inflammation and concurrent UACS. The cough will not resolve until all contributing causes are effectively treated. 1 Partial improvement with one treatment means continuing that therapy and adding the next intervention in the algorithm, rather than stopping and switching. 1