A 52-year-old man with newly diagnosed hypertension is started on an ACE inhibitor. After 2 weeks, he develops a persistent dry cough. Which investigation is most appropriate to confirm drug-induced cough and rule out alternative causes?

Explanation

## Investigation of ACE Inhibitor–Induced Cough ### Clinical Context ACE inhibitor–induced cough is a common adverse effect occurring in 5–10% of patients, caused by accumulation of bradykinin in the lungs. However, persistent cough warrants investigation to exclude serious alternative diagnoses. ### Why Chest X-ray and HRCT? **Key Point:** Chest imaging is the investigation of choice to differentiate drug-induced cough from pulmonary pathology (pneumonia, pulmonary edema, malignancy, tuberculosis, interstitial lung disease). **Clinical Pearl:** ACE inhibitor–induced cough is a diagnosis of exclusion. Imaging must be performed before attributing the symptom to the drug, especially if the cough is productive, associated with fever, or accompanied by respiratory distress. **High-Yield:** The cough typically: - Develops within days to weeks of ACE inhibitor initiation - Resolves within 1–4 weeks of drug discontinuation - Is non-productive and persistent - Does not require specific treatment beyond stopping the ACE inhibitor ### Diagnostic Algorithm ```mermaid flowchart TD A[ACE inhibitor-induced cough suspected]:::outcome --> B{Cough characteristics?}:::decision B -->|Dry, non-productive, no systemic signs| C[Chest X-ray]:::action B -->|Productive, fever, dyspnea, or abnormal signs| D[Chest X-ray + HRCT]:::action C -->|Normal| E[Likely drug-induced]:::outcome D -->|Normal| E C -->|Abnormal| F[Alternative diagnosis identified]:::outcome D -->|Abnormal| F E --> G[Stop ACE inhibitor, switch to ARB or alternative]:::action F --> H[Treat underlying condition]:::action ``` ### Why Other Options Are Suboptimal | Investigation | Limitation | |---|---| | Serum ACE levels & angiotensin II | Not diagnostic for cough; ACE inhibitors work by blocking ACE, not by changing circulating levels in a way that predicts cough | | 24-hour ABPM | Assesses BP control, not the cause of cough | | Serum creatinine & potassium | Monitor for renal/electrolyte complications, not diagnostic for cough etiology | **Tip:** Remember that ACE inhibitor–induced cough is benign and reversible. The goal of imaging is to exclude serious underlying pathology before attributing symptoms to the drug.