Why are patients with a pheochromocytoma often hyperglycemic?

Patients with pheochromocytoma are often hyperglycemic because this tumor secretes large amounts of catecholamines. These hormones cause increased glycogenolysis, gluconeogenesis, and impaired peripheral glucose utilization. In other words, there is increased glucose production by the liver as well as decreased ability of the peripheral tissues to take up this glucose, resulting in hyperglycemia.

Additionally, catecholamines can inhibit insulin secretion which further adds to the hyperglycemia.