Differential Diagnosis

• Single most likely diagnosis
  • Atherosclerosis: Given the patient's history of bilateral femur avascular necrosis (AVN) and now presenting with left subclavian artery thrombosis and symptoms suggestive of posterior circulation stroke, atherosclerosis is a strong consideration. The history of AVN could be related to long-standing steroid use or other risk factors that also predispose to atherosclerosis.
• Other Likely diagnoses
  • Hypercoagulable state: Conditions such as Factor V Leiden, antithrombin III deficiency, or protein C/S deficiency could lead to recurrent thrombotic events, including the AVN and the current subclavian artery thrombosis.
  • Vasculitis (e.g., Takayasu arteritis): Although less common, vasculitis could explain both the AVN (through vascular inflammation) and the subclavian artery thrombosis, especially if there's a history of systemic symptoms or other vascular involvement.
  • Paroxysmal Nocturnal Hemoglobinuria (PNH): A rare cause of thrombosis, PNH could potentially explain the AVN and the arterial thrombosis, though it would be less likely without other supporting evidence like hemolytic anemia.
• Do Not Miss diagnoses
  • Thromboembolic disease (e.g., paradoxical embolism): Given the patient's presentation with stroke and limb ischemia, it's crucial to consider sources of embolism, including cardiac (e.g., atrial fibrillation) or paradoxical embolism through a patent foramen ovale.
  • Aortic dissection: Although the primary complaint involves the subclavian artery, aortic dissection could lead to similar symptoms, including limb ischemia and stroke, and is a medical emergency.
  • Fibromuscular dysplasia: A condition affecting medium and large arteries, it could lead to thrombosis and ischemic events, including stroke.
• Rare diagnoses
  • Ehlers-Danlos syndrome: A genetic disorder affecting connective tissue, it could potentially lead to vascular complications, including aneurysms and thrombosis, though it's much less common.
  • Homocystinuria: A genetic disorder leading to elevated homocysteine levels, which is a risk factor for thrombosis and could potentially explain the patient's presentation, though it's rare and typically presents with other systemic manifestations.
  • Antiphospholipid syndrome: An autoimmune disorder that increases the risk of thrombosis, it could be a consideration, especially if there's a history of recurrent thrombotic events or other autoimmune symptoms.