Differential Diagnosis for a 56-year-old Male with Chest Pain, Dizziness, Dyspnea, Fever, and Nausea

Single Most Likely Diagnosis

• Acute Pericarditis: The presence of chest pain, pericardial friction rub, fever, and electrical alternans on ECG are highly suggestive of acute pericarditis, especially given the recent upper respiratory infection which could be a triggering factor.

Other Likely Diagnoses

• Pulmonary Embolism (PE): Although less likely given the normal chest X-ray and the presence of a pericardial friction rub, PE could explain dyspnea, chest pain, and hypotension. The recent history of an upper respiratory infection could be a risk factor for PE due to immobilization or hypercoagulability.
• Myocarditis: Given the recent upper respiratory infection, myocarditis is a possibility, especially with symptoms like chest pain, dyspnea, and fever. However, the presence of a pericardial friction rub and electrical alternans leans more towards pericarditis.

Do Not Miss Diagnoses

• Cardiac Tamponade: Although the patient is hypotensive and has a decrease in blood pressure with inspiration (pulsus paradoxus), which can be seen in cardiac tamponade, the absence of significant echocardiographic evidence (not mentioned but implied by the normal chest X-ray and the specific mention of pericardial friction rub) makes it less likely. However, cardiac tamponade is a life-threatening condition that must be considered, especially with hypotension and pulsus paradoxus.
• Aortic Dissection: This is a critical diagnosis to consider in any patient with chest pain and hypotension. Although less likely given the specific findings of pericardial friction rub and the clinical context, it's a condition that could present with similar symptoms and is often fatal if not promptly diagnosed and treated.

Rare Diagnoses

• Pneumonia with Complications: Although the chest X-ray is normal, atypical presentations of pneumonia, especially in older adults, can sometimes have a normal initial chest X-ray. The recent upper respiratory infection could be a predisposing factor.
• Lymphoma or Other Malignancies Involving the Pericardium: These conditions can cause pericarditis and cardiac tamponade but are less common and would typically have other systemic symptoms or findings on imaging studies.