A 58-year-old man presents to the primary care clinic complaining of a burning sensation in his hands and feet, which he describes as “hot and swollen” for the past few weeks. He also reports generalized intense itching that worsens significantly after taking a hot shower. Recently, he has been experiencing frequent headaches, dizziness, and a feeling of fullness in his left upper abdomen. His medical history is significant for well-controlled hypertension. He denies any history of smoking, venous or arterial thrombosis, or recent travel to high altitudes. His family history is unremarkable. On general appearance, he is a well-developed man who appears visibly ruddy with facial plethora, sitting comfortably on the examination table. His blood pressure is 142/88 mmHg, heart rate is 86 bpm, respiratory rate is 16 breaths per minute, and he is afebrile with an oxygen saturation of 98% on room air.