What are the differential diagnoses for an elderly, obese woman with a history of smoking, lung disease (including two episodes of pneumonia and one episode of COVID-19), presenting with sudden, severe pain in her right shoulder, around the shoulder blade, without trauma?

Differential Diagnoses for Sudden Severe Right Shoulder/Scapular Pain in an Elderly, Obese Woman with Smoking History and Lung Disease

The most critical differential to rule out immediately is pulmonary pathology—specifically pneumonia, pulmonary embolism, or pneumothorax—given this patient's high-risk profile (elderly, obese, smoking history, recurrent pneumonia, and COVID-19 history) where referred pain from diaphragmatic or pleural irritation can present as isolated shoulder pain. 1

Life-Threatening Differentials (Rule Out First)

Pulmonary Causes with Referred Pain

• Pneumonia with diaphragmatic irritation: Right lower lobe pneumonia can present as isolated right shoulder pain via C4 sensory fibers in the phrenic nerve, which shares the same dermatome as the shoulder/scapular region 2, 3
• Pulmonary embolism: Elderly, obese patients with recent COVID-19 are at significantly elevated risk for thromboembolic complications 1
• Spontaneous pneumothorax: Can occur in COVID-19 patients even without mechanical ventilation, presenting with sudden severe pain and subcutaneous emphysema 4
• COVID-19 complications: Post-acute sequelae can include persistent pulmonary inflammation, myocardial involvement, or thromboembolic events 1

Cardiovascular Causes

• Acute coronary syndrome: Elderly women with multiple risk factors (obesity, smoking) may present with atypical symptoms including isolated shoulder pain 1
• Aortic dissection: Sudden severe pain in an elderly patient with cardiovascular risk factors requires immediate consideration 1

Red Flags Requiring Immediate Evaluation

Look specifically for these clinical features:

• Respiratory symptoms: Shortness of breath, cough (especially productive with purulent sputum), fever, tachypnea >30 breaths/min, or SpO2 <90% 1
• Systemic signs: Fever, unusual fatigue, night sweats, or weight loss 2
• Cardiovascular instability: Tachycardia, hypotension, or chest pressure 1
• Physical examination findings: Decreased breath sounds, dullness to percussion, subcutaneous emphysema in neck/chest wall, or elevated body temperature 2, 4, 3

Diagnostic Algorithm

Step 1: Immediate Clinical Assessment

• Vital signs: Temperature, respiratory rate, oxygen saturation, blood pressure, heart rate 1
• Focused pulmonary examination: Auscultation for decreased breath sounds or crackles, percussion for dullness, palpation for subcutaneous emphysema 2, 3
• Cardiac examination: Rule out signs of acute coronary syndrome or heart failure 1
• Shoulder examination: Assess if pain is truly mechanical (worsens with shoulder movement) or referred (unchanged with shoulder ROM) 2, 3

Step 2: Initial Imaging

• Chest X-ray (first-line): Appropriate for this patient who likely has moderate-to-severe symptoms given "sudden severe pain"; can identify pneumonia, pneumothorax, pleural effusion, or cardiac silhouette abnormalities 1
• CT chest with contrast: Consider if chest X-ray is negative but clinical suspicion remains high, particularly for pulmonary embolism or early pneumonia 1

Step 3: Laboratory Evaluation

• Complete blood count: Leukocytosis suggests bacterial infection 5
• Cardiac biomarkers: Troponin if cardiac etiology suspected 1
• D-dimer: If pulmonary embolism is in differential 1
• Procalcitonin: Levels >0.5 ng/mL support bacterial infection 5
• Blood cultures: If fever present and antibiotics being considered 5

Musculoskeletal Differentials (Lower Priority Given Presentation)

Only consider after excluding life-threatening causes:

• Rotator cuff pathology: Less likely given sudden onset without trauma and patient's risk profile 2
• Cervical radiculopathy: Would typically have neck pain and neurological symptoms
• Adhesive capsulitis: Gradual onset, not sudden severe pain
• Fracture: Unlikely without trauma, though pathological fracture from malignancy possible in smoker

Common Pitfalls to Avoid

• Don't assume musculoskeletal origin: When shoulder examination findings are negative for mechanical pain (pain unchanged with shoulder movement), pulmonary pathology must be excluded 2, 3
• Don't miss atypical pneumonia presentation: Elderly patients may present with minimal respiratory symptoms but significant referred pain 3
• Don't overlook post-COVID complications: This patient's COVID-19 history places her at ongoing risk for thromboembolic events and persistent pulmonary inflammation even months after acute infection 1
• Don't delay imaging: Given this patient's high-risk profile (elderly, obese, smoking history, recurrent pneumonia), chest imaging should be obtained urgently rather than attempting conservative musculoskeletal management 1

Risk Stratification for This Patient

This patient has multiple high-risk features for severe pulmonary complications:

• Age: Elderly patients are at significantly higher risk for severe disease 1
• Obesity: Independent risk factor for poor respiratory outcomes 1
• Smoking history: Increases risk of bacterial superinfection and severe COVID-19 outcomes 1, 5
• Chronic lung disease: History of recurrent pneumonia and COVID-19 indicates compromised pulmonary reserve 1

Given this constellation of risk factors, pulmonary pathology should be considered the primary differential until proven otherwise through appropriate imaging and clinical evaluation.