In 98% of cases there is sustained or episodic hypertension (high blood pressure). True episodic hypertension occurs in less than 50% of cases. In truth, phaeochromocytomas are "great mimics" like syphilis in days old and not so old. The symptoms are explained by the adrenaline and noradrenaline released by the tumour.
An abrupt release of catecholamines from a phaeochromocytoma will cause a diffuse and powerful stimulation of adrenaline receptors around the body (massive sympathetic nervous system activation). Less than half of those affected by phaeochromocytomas will experience these paroxysms, which may last for a few minutes to several hours. During these attacks blood pressure will rise dramatically, and patients may experience the signs and symptoms mentioned above. In between attacks the blood pressure returns to normal, and the symptoms disappear. The episodic nature of the attacks is a guide in distinguishing phaeochromocytomas from chronic anxiety attacks. Certain drugs may cause signs and symptoms indistinguishable from a phaeochromocytoma crisis. These include clonidine withdrawal, monoamine oxidase inhibitors and of course the factitious use of adrenaline and noradrenaline (Munchhausen's syndrome).
There are certain triggers that may precipitate these attacks. Certain twisting movements, applying force to the area of the adrenal gland, and surgical procedures can all induce a paroxysm. Phaeochromocytomas in the bladder can present on passing urine as episodic hypertension. A phaeochromocytoma crisis is a medical emergency, and may cause sudden death.