The classification and nomenclature of autonomic disorders--ending chaos, resolving conflict and hopefully achieving clarity

Vascular Analysis of Individuals with Drop Attacks

The authors used magnetic resonance angiography to examine the intracranial and cervical vascular structures of individuals who suffer from drop attacks. Normal structural configurations of the circle of Willis and the vertebrobasilar arterial system were compared to the vascular patterns of 10 subjects with these episodic tonic or atonic attacks. Overall, multiple areas of arterial occlusion, stenosis, or hypoplasia were visualized in the images of 8 of the 10 subjects. Specific anomalies of the vertebral and basilar arteries were identified in 4 individuals, and 8 images depicted nonvisualization of the posterior communicating arteries. We suggest that the pathological aberrations in the regional circulation of the hindbrain support the hypothesis that a transient hypovolemic episode may have an impact upon the neural activity involved in maintenance of motor tone and postural stability.

Orthostatic hypotension: definition, diagnosis and management

Orthostatic hypotension commonly affects elderly patients and those suffering from diabetes mellitus and Parkinson's disease. It is a cause of significant morbidity in the affected patients. The goal of this review is to outline the pathophysiology, evaluation, and management of the patients suffering from orthostatic hypotension.

Dysautonomia in Parkinson disease

Dysautonomias are conditions in which altered function of one or more components of the autonomic nervous system (ANS) adversely affects health. This review updates knowledge about dysautonomia in Parkinson disease (PD). Most PD patients have symptoms or signs of dysautonomia; occasionally, the abnormalities dominate the clinical picture. Components of the ANS include the sympathetic noradrenergic system (SNS), the parasympathetic nervous system (PNS), the sympathetic cholinergic system (SCS), the sympathetic adrenomedullary system (SAS), and the enteric nervous system (ENS). Dysfunction of each component system produces characteristic manifestations. In PD, it is cardiovascular dysautonomia that is best understood scientifically, mainly because of the variety of clinical laboratory tools available to assess functions of catecholamine systems. Most of this review focuses on this aspect of autonomic involvement in PD. PD features cardiac sympathetic denervation, which can precede the movement disorder. Loss of cardiac SNS innervation occurs independently of the loss of striatal dopaminergic innervation underlying the motor signs of PD and is associated with other nonmotor manifestations, including anosmia, REM behavior disorder, orthostatic hypotension (OH), and dementia. Autonomic dysfunction in PD is important not only in clinical management and in providing potential biomarkers but also for understanding disease mechanisms (e.g., autotoxicity exerted by catecholamine metabolites). Since Lewy bodies and Lewy neurites containing alpha-synuclein constitute neuropathologic hallmarks of the disease, and catecholamine depletion in the striatum and heart are characteristic neurochemical features, a key goal of future research is to understand better the link between alpha-synucleinopathy and loss of catecholamine neurons in PD.

Blood pressure disorders during Parkinson’s disease: epidemiology, pathophysiology and management

Blood pressure disorders are highly prevalent in the course of Parkinson's disease (PD). They relate to autonomic failure and are frequently associated with orthostatic hypotension, postprandial hypotension and supine hypertension. Supine hypertension, which may concern up to 50% of patients with PD and autonomic failure, is driven by residual sympathetic activity and changes in sensitivity of vascular adrenergic receptors. It can also be induced or worsened by antihypotensive drugs. Even if little data is available, a set of arguments suggests that supine hypertension sometimes requires treatment. This review will focus on recent data on the pathophysiology and the management of supine hypertension in the context of its association with orthostatic hypotension.

Arterial hypertension, a tricky side of Parkinson's disease: physiopathology and therapeutic features

The role of arterial hypertension (HT) as risk factor for Parkinson's disease (PD) is still debated. Case-control and retrospective studies do not support an association between HT and PD and the risk of PD seems to be lower in hypertensive than in normotensive subjects. In addition, the use of calcium-channel blockers (CCBs) and angiotensin-converting enzyme inhibitors seems to have a protective effect on the risk of developing PD. In clinical practice, a crucial finding in subjects with PD is the high supine systolic blood pressure (SBP) coupled with orthostatic hypotension (OH). It is not clear whether this SBP load could be a risk factor for target organ damage as this load can be largely due to the drugs used to treat OH (i.e., fludrocortisone acetate, midodrine) or PD itself (i.e., monoamine oxidase inhibitors, dopamine D2-receptor antagonists). This blood pressure (BP) load is largely independent of medications as the 40 % of subjects with PD have a non-dipping pattern of BP during 24 h ambulatory monitoring (24-h ABPM). In PD, nocturnal HT is usually asymptomatic and 24-h ABPM should be used to track both supine HT and OH. Treatment of HT in PD is difficult because the reduction of supine BP could worsen OH. To avoid this, short-acting dihydropyridine CCBs, clonidine or nitrates are recommended, assuming between meals, in late afternoon or in the evening in avoiding an aggravation in the post-prandial hypotension characteristic of PD.

Lower limb and abdominal compression bandages prevent progressive orthostatic hypotension in elderly persons: a randomized single-blind controlled study

OBJECTIVES

This study sought to assess the efficacy of compression bandage of legs and abdomen in preventing hypotension and symptoms.

BACKGROUND

Progressive orthostatic hypotension can occur in elderly people during standing.

METHODS

Twenty-one patients (70 +/- 11 years) affected by symptomatic progressive orthostatic hypotension underwent 2 tilt-test procedures, with and without elastic bandage of the legs (compression pressure 40 to 60 mm Hg) and of the abdomen (compression pressure 20 to 30 mm Hg) in a randomized crossover fashion. Leg bandage was administered for 10 min and was followed by an additional abdominal bandage for a further 10 min. Symptoms were evaluated by a 7-item Specific Symptom Score (SSS) questionnaire before and after 1 month of therapy with elastic compression stockings of the legs (prescribed in all patients irrespective of the results of the tilt study).

RESULTS

In the control arm, systolic blood pressure decreased from 125 +/- 18 mm Hg immediately after tilting to 112 +/- 25 mm Hg after 10 min of sham leg bandage and to 106 +/- 25 mm Hg after 20 min despite the addition of sham abdominal bandage. The corresponding values with active therapy were 129 +/- 19 mm Hg, 127 +/- 17 mm Hg (p = 0.003 vs. control), and 127 +/- 21 mm Hg (p = 0.002 vs. control). In the active arm, 90% of patients remained asymptomatic, versus 53% in the control arm (p = 0.02). During the month before evaluation, the mean SSS score was 35.2 +/- 12.1 with dizziness, weakness, and palpitations accounting for 64% of the total score. The SSS score decreased to 22.5 +/- 11.3 after 1 month of therapy (p = 0.01).

CONCLUSIONS

Lower limb compression bandage is effective in avoiding orthostatic systolic blood pressure decrease and in reducing symptoms in elderly patients affected by progressive orthostatic hypotension.

Neurocirculatory Abnormalities in Parkinson Disease With Orthostatic Hypotension

Patients with Parkinson disease often have orthostatic hypotension. Neurocirculatory abnormalities underlying orthostatic hypotension might reflect levodopa treatment. Sixty-six Parkinson disease patients (36 with orthostatic hypotension, 15 off and 21 on levodopa; 30 without orthostatic hypotension) had tests of reflexive cardiovagal gain (decrease in interbeat interval per unit decrease in systolic pressure during the Valsalva maneuver; orthostatic increase in heart rate per unit decrease in pressure); reflexive sympathoneural function (decrease in pressure during the Valsalva maneuver; orthostatic increment in plasma norepinephrine); and cardiac and extracardiac noradrenergic innervation (septal myocardial 6-[ 18 F]fluorodopamine-derived radioactivity; supine plasma norepinephrine). Severity of orthostatic hypotension did not differ between the levodopa-untreated and levodopa-treated groups with Parkinson disease and orthostatic hypotension (−52±6 [SEM] versus −49±5 mm Hg systolic). The 2 groups had similarly low reflexive cardiovagal gain (0.84±0.23 versus 1.33±0.35 ms/mm Hg during Valsalva; 0.43±0.09 versus 0.27±0.06 bpm/mm Hg during orthostasis); and had similarly attenuated reflexive sympathoneural responses (97±29 versus 71±23 pg/mL during orthostasis; −82±10 versus −73±8 mm Hg during Valsalva). In patients off levodopa, plasma norepinephrine was lower in those with (193±19 pg/mL) than without (348±46 pg/mL) orthostatic hypotension. Low values for reflexive cardiovagal gain, sympathoneural responses, and noradrenergic innervation were strongly related to orthostatic hypotension. Parkinson disease with orthostatic hypotension features reflexive cardiovagal and sympathoneural failure and cardiac and partial extracardiac sympathetic denervation, independent of levodopa treatment.

Clinical pharmacokinetics of the norepinephrine precursor L-threo-DOPS in primary chronic autonomic failure

BACKGROUND

Oral L-threo-3,4-dihydroxyphenylserine (L-DOPS), a synthetic catechol amino acid, increases standing blood pressure and improves standing ability in patients with neurogenic orthostatic hypotension, by conversion of L-DOPS to norepinephrine (NE) outside the brain. This study assessed the pharmacokinetics of L-DOPS, NE, and dihydroxyphenylglycol (DHPG), the main neuronal metabolite of NE, in patients with primary chronic autonomic failure from pure autonomic failure (PAF) or multiple system atrophy (MSA).

METHODS

In 5 MSA and 4 PAF patients, antecubital venous blood was drawn during supine rest and plasma levels of catechols measured at various times for 48 hours after a single oral dose of 400 mg of L-DOPS.

RESULTS

Plasma L-DOPS peaked at 1.9 microg/ml (9 micromol/L) about 3 hours after drug administration, followed by a monoexponential decline with a half-time of 2-3 hours in both patient groups. Plasma NE and DHPG also peaked at about 3 hours, but at much lower concentrations (4 and 42 nmol/L). Compared to the MSA group, the PAF group had a smaller calculated volume of distribution of L-DOPS and up to 10-fold lower plasma NE levels at all time points. Plasma NE was above baseline in MSA even at 48 hours after L-DOPS.

CONCLUSIONS

The relatively long half-time for disappearance of L-DOPS compared to that of NE explains their very different attained plasma concentrations. The similar NE and DHPG responses in PAF and MSA suggests production of NE from LDOPS mainly in non-neuronal cells. Persistent elevation of plasma NE in MSA suggests residual release of NE from sympathetic nerves.

Postural Blood Pressure Changes and Orthostatic Hypotension in the Elderly Patient

With age our ability to maintain haemodynamic homeostasis during position changes becomes less effective. This predisposes elderly patients to significant changes in blood pressure upon standing and orthostatic hypotension (OH). The prevalence of OH varies according to the population being studied. A range of between 5% and 60% has been reported with the lower rate in elderly individuals living in the community and higher rates in those living in an institution or in the acute-care setting. Multiple factors have been linked to OH including age, bed rest, low body mass index and medications. Although antihypertensive medications can theoretically, as a group, worsen OH, the majority of cross-sectional studies have found no association. In addition, prospective randomised trials have demonstrated an improvement in postural blood pressure (PBP) changes with antihypertensive medications. When considering the individual classes, peripheral vasodilators, specifically alpha-adrenoceptor antagonists and nondihydropyridine calcium channel antagonists, can exacerbate PBP changes and lead to OH. ACE inhibitors, angiotensin-receptor antagonists and beta-adrenoceptor antagonists with intrinsic sympathomimetic activity are less likely to worsen OH. Careful management of electrolyte disturbance can decrease the risk of developing OH with diuretic use. With the aging population, this problem will be encountered by the clinicians at a much higher rate. A detailed patient history, an accurate orthostatic blood pressure measurement and careful evaluation of the autonomic nervous system can provide clinical guidance for management of OH. In hypertensive individuals with no pre-treatment OH, the use of antihypertensive medication can be safe and lead to a low risk of developing OH. In individuals with pre-treatment OH or who develop OH while on antihypertensive medications avoidance of the classes that may exacerbate OH and a judicious use of antihypertensive classes that may improve PBP changes may be safe and adequate treatment.

Functional Neuroimaging of Sympathetic Innervation of the Heart

Many concepts about acute and chronic effects of stress depend on alterations in sympathetic nerves supplying the heart. Physiologic, pharmacologic, and neurochemical approaches have been used to evaluate cardiac sympathetic function. This article describes a fourth approach that is based on nuclear scanning to visualize cardiac sympathetic innervation and function and relationships between the neuroimaging findings and those from other approaches. Multiple-system atrophy with orthostatic hypotension (formerly the Shy-Drager syndrome) features normal cardiac sympathetic innervation and normal entry of norepinephrine into the coronary sinus (cardiac norepinephrine spillover), in contrast to Parkinson disease with orthostatic hypotension, which features neuroimaging and neurochemical evidence for loss of cardiac sympathetic nerves. This difference may have important implications not only for diagnosis but also for understanding the etiology of Parkinson disease. By analysis of curves relating myocardial radioactivity with time (time-activity curves) after injection of a sympathoneural imaging agent, it is possible to obtain information about cardiac sympathetic function. Abnormal time-activity curves are seen in common disorders such as heart failure and diabetic neuropathy and provide an independent, adverse prognostic index. Analogous abnormalities might help explain increased cardiovascular risk in psychiatric disorders such as melancholic depression.

Dysautonomia in Parkinson's disease: neurocardiological abnormalities

Symptoms of abnormal autonomic-nervous-system function occur commonly in Parkinson's disease (PD). Orthostatic hypotension in patients with parkinsonism has been thought to be a side-effect of treatment with levodopa, a late stage in the disease progression, or, if prominent and early with respect to disordered movement, an indication of a different disease, such as multiple system atrophy. Instead, patients with PD and orthostatic hypotension have clear evidence for baroreflex failure and loss of sympathetic innervation, most noticeably in the heart. By contrast, patients with multiple system atrophy, which is difficult to distinguish clinically from PD, have intact cardiac sympathetic innervation. Post-mortem studies confirm this distinction. Because PD involves postganglionic sympathetic noradrenergic lesions, the disease seems to be not only a movement disorder with dopamine loss in the nigrostriatal system of the brain, but also a dysautonomia, with norepinephrine loss in the sympathetic nervous system of the heart.

Association between supine hypertension and orthostatic hypotension in autonomic failure

Supine hypertension occurs commonly in primary chronic autonomic failure. This study explored whether supine hypertension in this setting is associated with orthostatic hypotension (OH), and if so, what mechanisms might underlie this association. Supine and upright blood pressures, hemodynamic responses to the Valsalva maneuver, baroreflex-cardiovagal gain, and plasma norepinephrine (NE) levels were measured in pure autonomic failure (PAF), multiple-system atrophy (MSA) with or without OH, and Parkinson's disease (PD) with or without OH. Controls included age-matched, healthy volunteers and patients with essential hypertension or those referred for dysautonomia. Baroreflex-cardiovagal gain was calculated from the relation between the interbeat interval and systolic pressure during the Valsalva maneuver. PAF, MSA with OH, and PD with OH all featured supine hypertension, which was equivalent in severity to that in essential hypertension, regardless of fludrocortisone treatment. Among patients with PD or MSA, those with OH had higher mean arterial pressure during supine rest (109+/-3 mm Hg) than did those lacking OH (96+/-3 mm Hg, P=0.002). Baroreflex-cardiovagal gain and orthostatic increments in plasma NE levels were markedly decreased in all 3 groups with OH. Among patients with PD or MSA, those with OH had much lower mean baroreflex-cardiovagal gain (0.74+/-0.10 ms/mm Hg) than did those lacking OH (3.13+/-0.72 ms/mm Hg, P=0.0002). In chronic autonomic failure, supine hypertension is linked to both OH and low baroreflex-cardiovagal gain [corrected]. The finding of lower plasma NE levels in patients with than without supine hypertension suggests involvement of pressor mechanisms independent of the sympathetic nervous system.

Neurocardiovascular instability in cognitive impairment and dementia

Neurocardiovascular instability (NCVI, neurally mediated disorders causing hypotension with or without bradycardia) represents abnormal neural control of the cardiovascular system and presents as dizziness, syncope, or falls. The mechanisms underpinning NCVI are incompletely understood. The three most common disorders are carotid sinus syndrome (CSS), orthostatic hypotension (OH), and vasovagal syndrome (VVS): CSS, cardioinhibition > 3 s and/or vasodepressor response > or = 50 mmHg drop in systolic pressure during carotid sinus stimulation; OH: fall in systolic blood pressure > 20 mmHg during standing; VVS: cardioinhibition > 3 s and/or vasodepressor response > 50 mmHg during prolonged head-up tilting. In fallers with cognitive impairment or dementia, the prevalence of NCVI is 70%. Multifactorial interventions, including treatment of NCVI, significantly reduce falls and syncope. The predominant components of NCVI in fallers with cognitive impairment and dementia are CSS and OH. In Lewy body and Alzheimer's dementia, the prevalence of NCVI is up to 60%, again predominantly CSS and OH. The prevalence of cardioinhibitory carotid sinus hypersensitivity is particularly high in Lewy body dementia-41% compared with 12% in Alzheimer's disease and 3% in case controls. In addition, patients with Lewy body dementia have greater heart rate slowing (>2 s) and falls in systolic blood pressure (>20 mmHg) than those with Alzheimer's disease or controls during carotid sinus stimulation. The extent of deep white matter hyperintensities on MRI correlates with systolic fall during carotid sinus stimulation (R = 0.58; p < 0.005), suggesting a possible causal association between bradyarrhythmia-induced hypotension and microvascular pathology. NCVI is common in patients with dementia and may be a reversible cause of falls and syncope. Repeated hypotensive episodes may exaggerate cognitive decline in these patients.

Syncope resulting from autonomic insufficiency syndromes associated with orthostatic intolerance

The disorders of autonomic control associated with orthostatic intolerance are a diverse group that can result in syncope and near-syncope. A basic understanding of these disorders is essential to diagnosis and proper treatment. Ongoing studies should help to define better the spectrum of these disorders and to elaborate better diagnostic and treatment modalities.

Decreased sympathetic inhibition in gastroesophageal reflux disease

This study was undertaken to evaluate autonomic nervous system function in patients with gastroesophageal reflux disease. Based on clinical criteria, 28 consecutive patients with no history of heart, metabolic, or neurologic disease (mean age 41 y, range 20-62 y) reporting with upper gastrointestinal symptoms typical of gastroesophageal reflux underwent esophageal manometry, ambulatory 24-hour pH study with electrocardiographic monitoring, power spectral analysis of heart rate variability, and cardiovascular tests. Twelve healthy subjects served as controls. A positive result of prolonged esophageal pH study (pH in the distal esophagus less than 4, lasting more than 4.2% of recording time) was observed in 21 patients (reflux group); seven patients were categorized in the nonreflux group. No patient showed arrhythmias or any correlation between heart rate variability changes during electrocardiographic monitoring and episodes of reflux (pH less than 4, lasting more than 5 minutes). A decrease of sympathetic function occurred only in the reflux group (p <0.05) supported by the lower increase of systolic/diastolic blood pressure at sustained handgrip. No other cardiovascular tests showed statistically significant differences in the control or nonreflux groups. Total time reflux showed an inverse correlation with sympathetic function in the reflux group (r = -0.415, p <0.028). We concluded that there is some evidence for a slightly decreased sympathetic function in patients with gastroesophageal reflux disease that is inversely correlated with total time reflux. In these patients, decreased sympathetic function may cause dysfunction of intrinsic inhibitory control with increased transient spontaneous lower-esophageal sphincter relaxations, thus resulting in gastroesophageal reflux disease.

Noninvasive detection of sympathetic neurocirculatory failure

In sympathetic neurocirculatory failure (SNF), reflexive sympathetically mediated cardiovascular stimulation does not compensate for decreased cardiac filling. This explains orthostatic hypotension in chronic primary autonomic failure (CPAF). During phase 2 of the Valsalva maneuver (phase 2_L), blood pressure increases from its peak. During phase 4, blood pressure normally "overshoots" the baseline. Because these changes depend on sympathetically mediated cardiovascular stimulation, a progressive decrease in pressure during phase 2 and absence of the overshoot in phase 4 may indicate SNF. Moreover, because beat-to-beat blood pressure can be measured noninvasively using a photoplethysmographic or tonometric device, evaluating reflexive pressure responses might enable noninvasive diagnosis of SNF. This study assessed the relative frequencies of abnormal phase 2_L and phase 4 blood pressure in patients with CPAF and orthostatic hypotension and whether noninvasive measurement of beat-to-beat blood pressure can be used to diagnose SNF in patients. Twenty patients with chronic primary autonomic failure and orthostatic hypotension and 50 comparison patients, including several with CPAF but lacking orthostatic hypotension, underwent arterial pressure monitoring during performance of the Valsalva maneuver. Of the 20 patients with CPAF and orthostatic hypotension, all had an abnormal phase 2_L or phase 4 pressure response (sensitivity 100%), whereas only 3 of the 50 comparison patients had an abnormal response in either phase (specificity 94%). Seventeen patients with CPAF and orthostatic hypotension had abnormal responses in both phases (sensitivity 85%), but none of the comparison patients had such findings in both phases (specificity 100%). Of 13 patients in whom beat-to-beat blood pressure was recorded simultaneously invasively and noninvasively, all had abnormal blood pressure responses during phase 2_L and phase 4, whereas none of 29 comparison patients had such symptoms. Detection of abnormal blood pressure responses during phase 2_L or phase 4 of the Valsalva maneuver is a highly sensitive test for SNF. Abnormal pressure during these phases appears to identify SNF specifically. Noninvasive measurements can detect both of these abnormalities.

Pathophysiology and differential diagnosis of neurocardiogenic syncope

Syncope, the transient loss of consciousness and postural tone, is both a sign and a syndrome and may result from very diverse causes. Over the last decade, considerable attention has been focused on neurocardiogenic syncope, also known as vasovagal syncope. Research has demonstrated that the disorder is one aspect of a much broader group of disturbances of the autonomic nervous system that may lead to hypotension, orthostatic intolerance, and ultimately syncope. Recent discoveries have caused us to reevaluate our classification of autonomic disorders and to develop a new system that reflects current knowledge. A basic understanding of syncope and related disorders is essential to diagnosis and proper treatment. This article provides an overview of these conditions, their pathophysiology, and diagnosis.

Clinical disorders of the autonomic nervous system associated with orthostatic intolerance: an overview of classification, clinical evaluation, and management

The disorders of autonomic control associated with orthostatic intolerance are a diverse group of infirmities that can result in syncope and near syncope (as well as a host of other complaints). A basic understanding of these disorders is essential to both diagnosis and proper treatment. These infirmities are not new, what has changed is our ability to recognize them. It has been said that "the world undergoes change in the human consciousness. As this consciousness changes, so does the world." On going studies will continue to help better define the broad spectrum of these disorders, and to elaborate better diagnostic and treatment modalities.

Dysautonomic and reflex syncope syndromes

Both dysautonomic and reflex syncope are common problems that, although related to neurocardiogenic syncope, are somewhat distinct entities. Proper diagnosis and management require an adequate knowledge of these disorders. Further investigations will continue to advance knowledge of these various disorders of orthostatic control.

Sympathetic cardioneuropathy in dysautonomias

BACKGROUND

The classification of dysautonomias has been confusing, and the pathophysiology obscure. We examined sympathetic innervation of the heart in patients with acquired, idiopathic dysautonomias using thoracic positron-emission tomography and assessments of the entry rate of the sympathetic neurotransmitter norepinephrine into the cardiac venous drainage (cardiac norepinephrine spillover). We related the laboratory findings to signs of sympathetic neurocirculatory failure (orthostatic hypotension and abnormal blood-pressure responses associated with the Valsalva maneuver), central neural degeneration, and responsiveness to treatment with levodopa-carbidopa (Sinemet).

METHODS

Cardiac scans were obtained after intravenous administration of 6-[18F]fluorodopamine in 26 patients with dysautonomia. Fourteen had sympathetic neurocirculatory failure--three with no signs of central neurodegeneration (pure autonomic failure), two with parkinsonism responsive to treatment with levodopa-carbidopa, and nine with central neurodegeneration unresponsive to treatment with levodopa-carbidopa (the Shy-Drager syndrome). The rates of cardiac norepinephrine spillover were estimated on the basis of concentrations of intravenously infused [3H]norepinephrine during catheterization of the right side of the heart.

RESULTS

Patients with pure autonomic failure or parkinsonism and sympathetic neurocirculatory failure had no myocardial 6-[18F]fluorodopamine-derived radioactivity or cardiac norepinephrine spillover, indicating loss of myocardial sympathetic-nerve terminals, whereas patients with the Shy-Drager syndrome had increased levels of 6-[18F]fluorodopamine-derived radioactivity, indicating intact sympathetic terminals and absent nerve traffic. Patients with dysautonomia who did not have sympathetic neurocirculatory failure had normal levels of 6-[18F]fluorodopamine-derived radioactivity in myocardium and normal rates of cardiac norepinephrine spillover.

CONCLUSIONS

The results of 6-[18F]fluorodopamine positron-emission tomography and neurochemical analyses support a new clinical pathophysiologic classification of dysautonomias, based on the occurrence of sympathetic neurocirculatory failure, signs of central neurodegeneration, and responsiveness to levodopa-carbidopa.