Tuesday, June 10, 2008

What is Dysautonomia? What is POTS?

Almost everyone I know is confused about exactly what POTS and dysautonomia are. These disorders are extremely difficult to diagnose. Many people (including myself) go many years and dozens of doctors without any diagnosis at all. A lack of diagnosis can be exhausting, disheartening, and frustrating, only increasing the severity of symptoms and disability. It is important that anyone with a so-called “mystery diagnosis” not give up and keep searching for answers until they find someone who can help them. That’s not to say that you will like the diagnosis, but at least you will KNOW and can focus your efforts towards fighting your disease.

This post is crazy long, but aimed at explaining a little more about what these disorders are. It does get a bit “scienc-y”, but I am a vet after all! I will try not to put any other posts as long as this one on in the future unless under extreme duress.


What is Dysautonomia?

Dysautonomia is a dysfunction of the autonomic nervous system (ANS). Some of the disorders that are types of dysautonomia include POTS, neutrally mediated syncope, pure autonomic failure, multiple system atrophy, shy drager syndrome, and familial dysautonomia, among others.

According to the Merck Manual, the autonomic nervous system is the part of the nervous system that supplies the internal organs, including the blood vessels, stomach, intestine, liver, kidneys, bladder, genitals, lungs, pupils and muscles of the eye, heart, and sweat, salivary, and digestive glands. The autonomic nervous system has two main divisions: the sympathetic and the parasympathetic. After the autonomic nervous system receives information about the body and external environment, it responds by stimulating body processes, usually through the sympathetic division, or inhibiting them, usually through the parasympathetic division. The autonomic nervous system controls blood pressure, heart and breathing rates, body temperature, digestion, metabolism (thus affecting body weight), the balance of water and electrolytes (such as sodium and calcium), the production of body fluids (saliva, sweat, and tears), urination, defecation, sexual response, and other processes.

Autonomic disorders commonly cause dizziness or light-headedness due to an excessive decrease in blood pressure when a person stands (orthostatic hypotension). People may sweat Photo courtesy of NIAMS less or not at all and thus become intolerant of heat. The eyes and mouth may be dry. After eating, a person with an autonomic disorder may feel prematurely full or even vomit because the stomach empties very slowly (gastroparesis). Some people pass urine involuntarily (urinary incontinence), often because the bladder is overactive. Other people have difficulty emptying the bladder (urine retention) because the bladder is underactive. Constipation may occur, or control of bowel movements may be lost. The pupils may not dilate and narrow (constrict) as light changes.


What is POTS?

POTS, or Postural Orthostatic Tachycardia Syndrome, is a disorder characterized by a pulse rate that is too fast when the patient stands. POTS is a type of non-familial dysautonomia that is seen most commonly in relatively young (14-45) women (5:1 over men). The cause of each form of POTS is usually unknown. It is thought that approximately 500,000 Americans suffer with from some type of this disorder. It can be completely disabling, keeping many from standing, walking, driving, cooking, concentrating, working, or showering without assistance. While many are lucky enough to be able to manage their symptoms and have a relatively normal life, some people are severely disabled indefinitely. Some of the most common symptoms felt by people with POTS include:

Photo courtesy of Piero Sierra

*Altered vision (blurred, "white outs", "black outs") * Dizziness * Heart palpitations * Fatigue * Headache * Exercise intolerance (frequently post-exercise malaise) * Tremulousness * Nausea * Difficulty breathing or swallowing *Difficulty with digestion * Muscle pain * Neurocognitive deficits (confusion, lack of concentration, forgetfulness, etc) * Sweating * Sleep problems * Pallor * Heat intolerance * Fainting * Other vasomotor (blood vessel) symptoms

Understanding of POTS pathophysiology remains incomplete. The central finding is upright tachycardia with symptoms of orthostatic intolerance, although hypotension (in children) and resting tachycardia may also be present. That POTS is related to thoracic hypovolemia (low blood volume) is well established. Adults can experience hypertension; some individuals have both high and low BP.

POTS remains a syndrome; only thoracic hypovolemia is needed. Thus, dehydration might serve as a model for POTS. Indeed, a large fraction of patients with POTS have reduced blood volumes and paradoxical disturbances in the renin-angiotensin-aldosterone system.

Conversely, reduced intravascular volume can activate the autonomic nervous system; thus, the hypovolemia may be either the cause or the effect. Similar heart rate, BP, catecholamine (neurotransmitter) changes, and blood volume differences have been described in a subset of patients with POTS but not in others with relative hyporeninism. Supportive evidence from volume loading and vasoconstrictor experiments has shown transient success in remediating POTS. Similar interesting findings have also appeared in the Chronic Fatigue Syndrome literature. Although these findings have largely been interpreted within a framework of the hypothalamus-pituitary-adrenal axis, the findings also make sense within the POTS paradigm. (from emedicine Orthostatic Intolerance: An Overview at http://www.emedicine.com/ped/topic2860.htm).

An extremely helpful article for understanding POTS and its different forms and treatments is The Postural Tachycardia Syndrome: A Concise Guide to Diagnosis and Management by Grubb, B.D., Kanjwal,Y, and Kosinski, D.J. from the Journal of Cardiovascular Electrophysiology. 2006;17(1):108-112. According to this article:

The hallmark of these disorders is orthostatic intolerance, defined as the provocation of symptoms on standing, which are relieved when becoming supine. Patients often relate complaints of palpitations, exercise intolerance, fatigue, lightheadedness, tremor, headache, nausea, near syncope, and syncope.[2] Patients may be severely limited as activities such as housework, bathing, and even meals may exacerbate symptoms. Recent studies have shown that many patients with POTS may suffer the same degree of functional impairment as patients with chronic obstructive pulmonary disease or congestive heart failure, yet these patients are often misdiagnosed as having chronic anxiety or panic disorder.[3] POTS is classified as being either primary or secondary. The primary forms are idiopathic and not associated with other diseases. The secondary forms occur in association with a known disease or disorder. Proper recognition of subtypes is essential in management[4] (Fig. 1).

http://images.medscape.com/images/522/421/art-jce522421.fig1.gif


Pharmacotherapy is initiated with the goal of getting patients well enough to pursue reconditioning. No drug is currently approved by the US FDA for the treatment of POTS; therefore, any use of pharmacotherapy is done "off label." Knowing the subtype is important in choosing appropriate pharmacotherapy ( Table 3 ).

In the partial dysautonomic POTS, patient therapy is directed at augmenting fluid volume and increasing vascular resistance. We often begin with fludrocortisone, a mineral corticoid that promotes sodium and fluid retention, and also sensitizes peripheral alpha adrenergic receptors. The drug appears to be most helpful in younger patients. Next, we add a vasoconstrictor such as midodrine, starting at 5 mg orally three times a day. Since patients are most symptomatic early in the morning, we often advise patients to take their midodrine dose approximately 15 minutes prior to getting out of bed. We also advise patients that they can take an extra 5 mg dose as needed if severe breakthrough symptoms occur. If midodrine is not tolerated methylphenidate can be an effective alternative, especially because it comes in several long-acting preparations.

If patients continue to be symptomatic, we add either a serotonin reuptake inhibitor (SSRI) or a norepinephrine reuptake inhibitor. While the SSRIs are very useful in the prevention of neurocardiogenic syncope, the norepinephrine reuptake inhibitors are somewhat more helpful in POTS patients. We usually employ bupropion in the XL form. Of all the currently available SSRIs, we have noted that those with combined serotonin and norepinephrine reuptake inhibition (such as venlafaxine and duloxetine) are often the most effective. A very promising new therapy is pyridostigmine, an acetylcholinesterase inhibitor that facilitates neural transmission at the ganglionic level of both sympathetic and parasympathetic nerves. The drug is particularly useful in postviral POTS patients as well as patients with POTS secondary to a primary autoimmune disorder (such as Sjogren's syndrome or Lupus).

In severely affected patients, where other forms of therapy have either been poorly tolerated or ineffectual, we employ the drug erythropoietin. Originally developed for the treatment of anemia, it is also a potent vasoconstrictor that is quite useful in the treatment of orthostatic disorders. Due to the fact that erythropoietin (EPO) has to be administered by subcutaneous injection and because of its considerable expense, we normally reserve its use to patients who have proven refractory to or intolerant of other forms of therapy.

Another potential therapy is the somatostatin analog octreotide, which has potent vasoconstrictive effects. While some PD POTS patients may benefit from small doses of beta blockers (i.e., metoprolol 25 mg orally once or twice daily), the majority tend to feel worse on these agents.

The hyperadrenergic form of POTS is best treated by agents that block the release of norepinephrine or block its effects, such as clonidine. Labetalol is often effective, due to its alpha and beta blocking effects. Methyldopa is also helpful in select patients. Both the SSRIs and the norepinephrine reuptake inhibitors have been helpful in controlling patients' symptoms.

There is only limited data available at present on the prognosis of POTS patients. We are still in the process of following patients and analyzing their outcomes. Nonetheless some general trends have been noted. In patients suffering from postviral onset POTS, roughly one-half will make a good practical recovery over a 2–5 year period. Here, we define recovery as the relative absence of orthostatic symptoms with the ability to perform the normal activities of daily living with little or no restriction. However there are some patients that will not enjoy this degree of recovery and occasionally patients experience a progressive decline in functional status over time. In general, the younger the patient, the better the prognosis. In adolescents with the "developmental" form of POTS, approximately 75% will experience a significant recovery by the time they are in their early to mid-twenties. The vast majority of patients (~90%) will respond to a combination of physical therapy and pharmacotherapy. Patients with the hyperadrenergic form of POTS usually require treatment indefinitely. The prognosis of patients with the secondary POTS syndromes is usually determined by the prognosis of the underlying causative disorder.

The NDRF Handbook states that “Often these treatments, while helpful, do not bring the patients back to a sense of normal health. Over the course of months or even years, the patients can improve, or else they learn to cope with a chronic, debilitating, but not life-threatening disorder”. This extensive guide to the causes, symptoms, management, and coping for dysautonomias can be found at http://www.ndrf.org/NDRFHandbook.htm

NINDS states that “the prognosis for individuals with POTS varies. Many patients improve with treatment, although severe POTS can be disabling for years. The disorder is not thought to progress to a cardiac disease”. They have a very short synopsis of POTS symptoms, treatments, and prognosis at http://www.ninds.nih.gov/disorders/postural_tachycardia_syndrome/postural_tachycardia_syndrome.htm

So…now if you’ve gotten this far without falling asleep, you know some of the basics about dysautonomia and POTS. I could fill 200 pages with info about different ideas of what might be going on in POTS. More research is essential to getting anywhere. I’m going to stop now before everyone refuses to ever check my blog again! I hope this has been helpful in understanding a little more about what goes on in POTS and dysautonomia.

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