Pheochromocytoma (British English: phaeochromocytoma) is a rare tumor of the adrenal medulla composed of chromaffin cells and is a pharmacologically volatile, potentially lethal catecholamine-containing tumor of chromaffin tissue. It is part of the paraganglioma (PGL). These neuroendocrine tumors can be sympathetic, where they release catecholamines into the bloodstream which cause the most common symptoms, including hypertension (high blood pressure), tachycardia (fast heart rate), sweating, and headaches. Some PGLs may secrete little to no catecholamines, or only secrete paroxysmally (episodically), and other than secretions, PGLs can still become clinically relevant through other secretions or mass effect (most common with head and neck PGL). PGLs of the head and neck are typically parasympathetic and their sympathetic counterparts are predominantly located in the abdomen and pelvis, particularly concentrated at the organ of Zuckerkandl at the bifurcation of the aorta.
Signs and symptoms The symptoms of a sympathetic pheochromocytoma are related to sympathetic nervous system hyperactivity. The classic triad includes headaches (likely related to elevated blood pressure, or hypertension), tachycardia/elevated heart rate, and hyperhidrosis (excessive sweating, particularly at night). However, patients are unlikely to experience continuous symptoms. Due to the paroxysmal nature of catecholamine synthesis and release, patients may experience "attacks" or "spells" where they are suddenly overwhelmed with signs and symptoms of their tumor. Attacks can occur spontaneously (without warning) or may be triggered by a variety of pharmaceutical agents (including histamine, metoclopramide, glucagon, and adrenocorticotropic hormone), foods that contain tyramine (cheese and wine), intraoperative tumor manipulation, intubation, or during anesthetic induction.
Other clinical manifestations that have been reported include (in no particular order):
Pallor Heat intolerance Weight loss Chest or abdominal discomfort Palpitations Nausea/vomiting Constipation Orthostatic hypotension — becoming lightheaded or dizzy after swiftly changing positions Psychiatric manifestations Anxiety, panic attacks, nervousness, tremors Hyperglycemia (high blood sugar)
Complications While the symptoms of a pheochromocytoma are quite common, the disease has been referred to as "the great mimic". It is estimated that approximately 0.1% of patients with hypertension have a pheochromocytoma, and it is often misdiagnosed as essential hypertension. As symptoms are often paroxysmal (episodic/sporadic), patients may not immediately seek treatment as the problem "disappears on its own". Furthermore, when pictured in the ideal clinical scenario (an older woman in her mid-50s), the spontaneous attacks of flushing, sweating, and a racing heart may be mistaken for pre-menopausal related hot flashes. Unmanaged pheochromocytoma is dangerous and can lead to serious, potentially fatal complications, including stroke and hypertension-induced organ damage. The cardiovascular system is the most commonly involved. In pregnancy, pheochromocytoma is associated with significant maternal and fetal mortality, mainly due to hypertensive crisis in the mother and intrauterine growth restriction in the fetus. Misdiagnosis of pheochromocytoma can be deadly, as beta blockers, often prescribed for hypertension, can lead to unopposed alpha-adrenergic receptor stimulation in the context of pheochromocytoma. Most mortality associated with diagnosed pheochromocytoma came from surgery and hypertensive crisis, but mortality has greatly improved.
Cardiovascular system Hypertensive crisis: Pheochromocytoma-related hypertensive emergencies are one of the most feared clinical manifestations. Attacks are random and may occur secondary to a trigger (see Signs and Symptoms above) or spontaneously after a catecholamine surge. The prevailing symptom is elevated systolic blood pressure (> 200 mmHg) that is unresponsive to traditional treatment regimens and threatens end-organ damage. Patients require immediate, life-saving treatment to prevent further damage to other organs and/or death. Myocardial ischemia/Infarction: A heart attack is often caused by a significant build-up of plaque (atherosclerosis) in the coronary vessels. Patients with pheochromocytoma present with myocardial infarctions despite an overall lack of plaque build-up, indicating a different mechanism for the myocardial infarction. Current research hypothesizes that the tumor secretes massive amounts of catecholamines, which directly interact with myocardial (heart) tissue and exert negative effects, including oxygen deprivation, leading to accelerated scarring and cell death. Toxic myocarditis: Even in patients without myocardial damage, excessive catecholamines can result in abnormal ST changes on an ECG. Norepinephrine (a catecholamine) is hypothesized to result in damaged cardiac tissue by inhibiting coronary blood flow and depriving cells of oxygen, thus resulting in ischemic tissue. Fortunately, following tumor excision and the subsequent quelling of catecholamines, the damage has been proven reversible. Cardiomyopathy: Pheochromocytomas have been implicated in various types of cardiomyopathy, including myocarditis (see above), dilated cardiomyopathy, and stress-induced or Takotsubo cardiomyopathy. As with the other cardiovascular-related complications, excess catecholamines are responsible for the increased myocardial burden and significant physiologic stress. Current literature indicates that most of the catecholamine-induced damage is reversible, thereby strengthening the argument for early and accurate diagnosis to allow for cardiac remodeling and prevent further destruction. Arrhythmias: Sinus tachycardia is the most common abnormal heart rhythm associated with a pheochromocytoma and is experienced by patients as the feeling of a "fluttering heart" or palpitations. Many other tachyarrhythmias (fast heart rate) have also been reported.
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