What is the differential diagnosis for a 67-year-old man with a chronic cough who is not taking an angiotensin-converting enzyme inhibitor and has no infectious symptoms?

Differential Diagnosis for Chronic Cough in a 67-Year-Old Male

In this 67-year-old man with chronic cough, not on an ACE inhibitor and without infectious symptoms, focus your diagnostic workup on the "big three" causes: Upper Airway Cough Syndrome (UACS), asthma (including cough-variant asthma), and gastroesophageal reflux disease (GERD)—which together account for 92-100% of chronic cough cases in nonsmokers with normal chest X-rays 1.

Primary Differential Diagnoses

The Big Three (Account for >90% of cases)

1. Upper Airway Cough Syndrome (UACS) - formerly called post-nasal drip syndrome

   • Can present as "silent" with cough as the only symptom
   • Due to various rhinosinus conditions
   • Most common single cause in multiple international studies 1

2. Asthma (including cough-variant asthma)

   • May present with cough alone, without wheezing or dyspnea
   • "Silent" presentation is common
   • Requires spirometry and bronchoprovocation testing for diagnosis 1

3. Gastroesophageal Reflux Disease (GERD)

   • Can be "silent" without typical heartburn or regurgitation
   • Note: Acid suppression alone is no longer recommended for treatment 2
   • Often coexists with other causes

Important Additional Considerations

1. Nonasthmatic Eosinophilic Bronchitis (NAEB)

   • Prevalence ranges from 13-33% in international studies 1
   • Characterized by eosinophilic airway infiltration with normal spirometry
   • Diagnosed via induced sputum eosinophil count
   • Responds predictably to inhaled corticosteroids 1

2. Chronic Bronchitis/COPD

   • Particularly relevant given patient's age (67 years)
   • Must assess smoking history (current or former)
   • Requires spirometry for diagnosis 3, 4

Critical Red Flags to Exclude First

Before pursuing the common causes, immediately evaluate for these warning signs 2:

• Hemoptysis
• Smoker >45 years with new or changed cough (or coexisting voice disturbance)
• Adults 55-80 years with 30 pack-year history (current smoker or quit within 15 years) - this patient's age makes lung cancer screening criteria relevant
• Prominent dyspnea (especially at rest or nocturnal)
• Hoarseness
• Systemic symptoms: fever, weight loss
• Peripheral edema with weight gain
• Dysphagia
• Recurrent pneumonia

Initial Diagnostic Approach

Step 1: Essential History Elements

• Smoking status (current, former, pack-years)
• Medication review - confirm no ACE inhibitor use; also check for sitagliptin 2
• Environmental/occupational exposures 2
• Duration of cough (chronic = >8 weeks) 2
• Associated symptoms: post-nasal drip sensation, heartburn, wheezing, dyspnea
• Past medical history: COPD, asthma, prior malignancy, tuberculosis, AIDS 1

Step 2: Initial Testing

• Chest X-ray - mandatory to exclude masses, infiltrates, bronchiectasis 2, 4
• Spirometry with bronchodilator response 3, 4
• Exhaled nitric oxide (FeNO) - if available, helps identify eosinophilic inflammation 3
• Blood eosinophil count 3

Step 3: Empiric Treatment Trials (4-6 weeks each)

If initial testing is normal or near-normal, proceed with empiric treatment for the most likely causes 2, 3:

1. Trial for UACS: First-generation antihistamine/decongestant combination or intranasal corticosteroid
2. Trial for asthma: Inhaled corticosteroid ± bronchodilator
3. Trial for GERD: Proton pump inhibitor PLUS lifestyle modifications (note: PPI alone is insufficient) 2

Critical caveat: These conditions frequently coexist—up to 62% of patients have multiple simultaneous causes 1. If partial response occurs, continue that treatment and add therapy for the next most likely diagnosis.

Less Common but Important Causes

• Bronchiectasis - consider if productive cough with purulent sputum
• Interstitial lung disease - if abnormal chest imaging or restrictive pattern on spirometry
• Endobronchial lesions - tumors, sarcoidosis, tuberculosis
• Congestive heart failure - if peripheral edema present
• Post-infectious cough - though often resolves during workup; consider pertussis in epidemic settings 1
• Medication-induced - sitagliptin (DPP-4 inhibitor) in addition to ACE inhibitors 2

Common Pitfalls to Avoid

1. Don't rely on cough characteristics: The timing, character, or presence/absence of sputum production has NO diagnostic value 1

2. Don't assume single etiology: Multiple causes coexist in the majority of cases—if one treatment partially helps, add therapy for other likely causes rather than abandoning the first 1

3. Don't overlook "silent" presentations: UACS, asthma, and GERD commonly present with cough as the ONLY symptom 1

4. Don't order extensive testing prematurely: If no red flags and normal chest X-ray, empiric treatment trials are more cost-effective than extensive diagnostic workup 2, 3

5. Don't forget NAEB: This diagnosis requires induced sputum analysis but is easily treated with inhaled corticosteroids—consider early in the workup 1

When to Refer or Escalate

• Presence of any red flags - immediate evaluation for malignancy, tuberculosis, or other serious pathology 2
• Failure to respond after 4-6 weeks of appropriate empiric therapy 2
• Refractory or unexplained chronic cough - refer to specialized cough clinic 2, 3
• Abnormal chest imaging requiring CT or bronchoscopy 4

Follow-Up Strategy

Patients should be routinely followed within 4-6 weeks after initial evaluation to assess treatment response and adjust therapy 2. Use validated cough severity tools to objectively measure outcomes 2.