A 52-year-old woman with a 10-year history of rheumatoid arthritis (on methotrexate and sulfasalazine) presents with a 5-day history of progressive dyspnea and mild pleuritic chest pain. She denies leg swelling or recent travel. Vital signs: BP 128/82 mmHg, HR 102/min, RR 22/min, SpO₂ 94% on room air. Bilateral lower-limb examination is unremarkable. Chest X-ray shows a small left pleural effusion. D-dimer is 0.9 μg/mL (normal <0.5). ECG is normal. Arterial blood gas shows pH 7.42, PaCO₂ 32 mmHg, PaO₂ 72 mmHg, HCO₃⁻ 20 mEq/L. What is the most appropriate next diagnostic step?

Explanation

## Clinical Assessment **Key Point:** This patient has dyspnea, pleuritic chest pain, and an elevated D-dimer (0.9 μg/mL) despite normal ECG and stable hemodynamics. The combination of respiratory symptoms, abnormal gas exchange (PaO₂ 72 mmHg on room air), and elevated D-dimer mandates PE exclusion via imaging, even in the absence of classic DVT signs. **High-Yield:** D-dimer >0.5 μg/mL in a patient with dyspnea and chest pain has high sensitivity for PE (~95–98%) and warrants imaging. Normal D-dimer (<0.5) would allow safe exclusion of PE without further imaging. ## Why CTPA Is Indicated **Clinical Pearl:** Although this patient has rheumatoid arthritis (a risk factor for interstitial lung disease), the acute presentation with pleuritic pain, dyspnea, and elevated D-dimer is inconsistent with chronic ILD alone. PE must be excluded first because: 1. PE is an acute, life-threatening condition requiring immediate treatment 2. D-dimer elevation suggests acute thromboembolism 3. Pleural effusion can occur in PE (Hampton's hump, though rare) 4. Rheumatoid arthritis itself is a mild thrombotic risk factor (chronic inflammation) ## Differential Diagnosis & Reasoning | Finding | PE | RA-ILD | RA Pleuritis | CAP | | --- | --- | --- | --- | --- | | **D-dimer** | Elevated | Normal/mildly ↑ | Normal/mildly ↑ | May be ↑ | | **Onset** | Acute | Insidious | Acute/subacute | Acute | | **Pleural effusion** | Small, unilateral | Absent | Bilateral, exudative | Unilateral, exudative | | **ECG** | Often abnormal | Normal | Normal | Normal | | **CXR** | Often normal or wedge | Reticular opacities | Bilateral effusions | Lobar infiltrate | **Mnemonic:** PERIL = PE is Excluded by Ruling out Imaging (D-dimer + imaging algorithm) ## Diagnostic Algorithm ```mermaid flowchart TD A[Dyspnea + Pleuritic Chest Pain]:::outcome --> B[Check D-dimer]:::decision B -->|< 0.5 μg/mL| C[PE excluded clinically]:::outcome B -->|≥ 0.5 μg/mL| D[Obtain CTPA]:::action D --> E{PE confirmed?}:::decision E -->|Yes| F[Anticoagulation + ICU]:::action E -->|No| G[Pursue alternative diagnosis]:::action G --> H[Consider RA-ILD, pleuritis, CAP]:::outcome ``` **High-Yield:** In intermediate-risk patients (no shock, no DVT signs but elevated D-dimer), CTPA is the gold standard for PE diagnosis. Sensitivity and specificity both >95% [cite:Harrison 21e Ch 298].