Differential Diagnosis

The patient's symptoms, which include pain in the posterior left leg, swollen feet, increased blood pressure, decreased oxygen saturation, and shortness of breath, suggest a complex clinical picture that could be attributed to several conditions. Here's a categorized differential diagnosis:

• Single Most Likely Diagnosis

  • Deep Vein Thrombosis (DVT) with Pulmonary Embolism (PE): The patient's history of a long car ride (immobility), followed by leg pain and swelling, is highly suggestive of DVT. The subsequent development of shortness of breath, decreased oxygen saturation, and increased blood pressure could indicate a pulmonary embolism, which is a known complication of DVT. The normalization of blood pressure about 4 days later could be due to the body's compensation mechanisms or the start of treatment.

• Other Likely Diagnoses

  • Muscle Strain or Trauma: The initial pain in the posterior left leg could be due to a muscle strain from the long car ride, especially if the patient had to sit in an uncomfortable position for an extended period. However, this wouldn't fully explain the systemic symptoms that developed later.
  • Cellulitis: Infection of the skin and subcutaneous tissues could cause leg pain and swelling. While it could lead to systemic symptoms like fever and increased heart rate, it less commonly causes decreased oxygen saturation or increased blood pressure in the absence of sepsis.
  • Chronic Venous Insufficiency: This condition could cause leg swelling and pain, especially after prolonged periods of standing or sitting. However, it wouldn't typically cause acute shortness of breath or decreased oxygen saturation.

• Do Not Miss Diagnoses

  • Pulmonary Embolism (PE) without DVT: Even if DVT is not present or diagnosed, a PE could still occur, especially in the context of recent immobility. It's crucial to consider PE due to its high mortality rate if untreated.
  • Disseminated Intravascular Coagulation (DIC): Although less likely, DIC could present with leg pain (due to thrombosis) and systemic symptoms like shortness of breath and hypotension (in later stages). It's a condition that requires prompt recognition and treatment.
  • Cardiac Conditions (e.g., Heart Failure, Myocardial Infarction): These could cause shortness of breath, decreased oxygen saturation, and increased blood pressure. While they might not directly cause leg pain and swelling, they are critical to rule out due to their potential for severe outcomes.

• Rare Diagnoses

  • Thrombophlebitis: Inflammation of veins due to a blood clot, which could cause pain and swelling in the leg. It's less common than DVT but could potentially lead to PE.
  • Compartment Syndrome: A condition resulting from increased pressure within a muscle compartment, which could cause severe leg pain and swelling. It's less likely given the description but is a medical emergency if present.
  • Neoplastic Conditions: Certain cancers could increase the risk of thrombosis (Trousseau’s syndrome), but this would be less likely without other supporting evidence of malignancy.