Thursday, January 5, 2017
Postural orthostatic tachycardia syndrome (POTS)
Postural orthostatic tachycardia syndrome is attributed to autonomic failure in response to standing, without orthostatic hypotension. The underlying pathophysiology of POTS involves patchy, sympathetic denervation in the lower extremities and kidneys, which causes orthostatic venous pooling and relative hypovolemia. Cerebral and cardiac sympathetic innervations remain intact. The compensatory increase in cerebral sympathetic outflow leads to elevated norepinephrine (NE) levels, which result in an increase in HR, myocardial contractility, and the characteristic POTS symptoms of palpitations and lightheadedness. Evidence for partial dysautonomia includes abnormal thermoregulatory sweat and sudomotor reflex test results in the presence of intact autonomic adrenergic reflexes, which were demonstrated in more than 50% of patients diagnosed with POTS. Postural orthostatic tachycardia syndrome can be primary or secondary. The primary form is often idiopathic, and is categorized as neuropathic or hyperadrenergic. Neuropathic POTS is the most common primary form, and is usually precipitated by a febrile illness, sepsis, pregnancy, surgery, or trauma. The sympathetic response is not excessive, and serum NE levels may be high normal or slightly elevated. Some patients with neuropathic POTS may demonstrate a mild decrease in standing BP (<20/10 mm Hg) in addition to orthostatic tachycardia. The ganglionic acetylcholine receptor antibody is present in a substantial percentage of patients with neuropathic POTS, indicating a possible autoimmune etiology in some cases.
In hyperadrenergic POTS, the underlying pathophysiology involves excessive cerebral sympathetic outflow, mostly with patchy, peripheral sympathetic denervation, leading to a markedly elevated standing NE level (>600 pg/mL, and frequently >1000 pg/mL). Isolated, excessive sympathetic discharge was documented in some patients. Patients with hyperadrenergic POTS sometimes exhibit elevated standing BP, and more than 50% may also suffer from migraine headaches. Hyperadrenergic POTS is less common and has a more insidious course than the neuropathic type. This type of POTS is usually idiopathic, but it may be genetically linked and may be present in more than 1 family member. A point mutation in NE transport was documented in these patients, leading to excessively high serum NE levels because of a diminished clearance of NE
The secondary form of POTS occurs in association with a variety of other medical illnesses, such as diabetes mellitus, amyloidosis, sarcoidosis, alcoholism, lupus, Sjögren syndrome, chemotherapy, paraneoplastic syndrome, multisystem atrophy, or heavy metal poisoning. Prolonged bed rest and medications that impair autonomic regulation or NE levels (vasodilators, diuretics, antidepressants, anxiolytic agents, or central α-2 agonists) may also cause a secondary form of POTS.
Healthcare providers should be cognizant of POTS when treating young women who present with symptoms of orthostatic imbalance, particularly in the absence of orthostatic hypotension. Postural orthostatic tachycardia syndrome can be a chronic disease, and patients may present at either a physician’s office or an emergency department because of worsening symptoms. The diagnosis may be confirmed with a standing or tilt-table test. Because of the debilitating nature of the disease and its recurrent symptoms despite ongoing therapy, patients may feel discouraged and will benefit from both physical care and psychological support. Awareness of this syndrome is important in rendering the proper diagnosis and providing appropriate treatment for this autonomic disorder.