Bipolar Disorder as you are probably familiar manifests with extreme mood swings. Pheochromocytoma is a tumor of the adrenaline gland that episodically secretes high level of catecholamines. The sufferer presents with attacks of sweating, palpitations, nervousness and high blood pressure, somewhat similar to panic attacks. It is important to note that pheochromocytoma is rare.
When a patient with symptoms suggestive of bipolar disorder does not improve with mood stabilizers (Lithium, Depakote) the psychiatrist may consider other causes, for the mood swings. Medications, drugs or medical disorders may cause symptoms similar to bipolar. Pheochromocytoma is not likely to cause depressed mood as in bipolar and can be easily diagnosed by lab tests (presence of VMA metabolites).
Best wishes to your brother.
*Keywords: Bipolar, Pheochromocytoma