Differential Diagnosis for 91-year-old with Substernal Chest Pain, Small Left Pneumothorax, and Left Pleural Effusion

Single Most Likely Diagnosis

• Pulmonary Embolism (PE): Given the patient's age and presentation with substernal chest pain, a small pneumothorax, and a pleural effusion, PE is a leading consideration. The pleural effusion can be a complication of PE, especially if there is pulmonary infarction.

Other Likely Diagnoses

• Aortic Dissection: Although less common, aortic dissection can present with substernal chest pain and can lead to a pneumothorax or pleural effusion if there is involvement of the aorta near the lung or if there is a rupture into the thoracic cavity.
• Pneumonia: Community-acquired or hospital-acquired pneumonia can lead to pleural effusion and, in severe cases, can cause a pneumothorax, especially if there is necrosis of lung tissue.
• Lung Cancer: In an elderly patient, lung cancer with metastasis to the pleura or direct invasion of the pleura could explain the pleural effusion and, if there is necrosis or tumor erosion into the airway, could lead to a pneumothorax.

Do Not Miss Diagnoses

• Myocardial Infarction (MI): Although the presentation is atypical for MI, especially with a pneumothorax and pleural effusion, it's crucial not to miss an MI, as timely intervention can significantly improve outcomes.
• Pulmonary Arteriovenous Malformation (AVM) Rupture: Rare, but potentially life-threatening, rupture of a pulmonary AVM could present with hemoptysis, pneumothorax, and pleural effusion.
• Trauma: Even minor trauma in an elderly patient could lead to a pneumothorax and pleural effusion, especially if there are underlying lung diseases.

Rare Diagnoses

• Lymphangioleiomyomatosis (LAM): A rare lung disease that primarily affects women, leading to cystic lung lesions and can cause pneumothoraces.
• Eosinophilic Granuloma with Langerhans Cell Histiocytosis: Part of a spectrum of diseases that can cause lung cysts and pneumothoraces.
• Catamenial Pneumothorax: Associated with endometriosis, this condition can cause recurrent pneumothoraces in women, typically around the time of menstruation, though it's extremely rare and less likely in a 91-year-old patient.

Each of these diagnoses requires careful consideration of the patient's history, physical examination, and diagnostic tests such as CT scans, echocardiography, and possibly angiography or bronchoscopy to determine the specific etiology of the symptoms.