Autonomic Sweat Responses in REM Sleep Behavior Disorder and Parkinsonism

The value of electrochemical skin conductance measurement by Sudoscan® for assessing autonomic dysfunction in peripheral neuropathies beyond diabetes

The diagnosis and follow-up of peripheral neuropathies involving small-diameter nerve fibers require specific examinations beyond conventional nerve conduction studies which only concern large-diameter nerve fibers. Among these tests, some are dedicated to the investigation of cutaneous innervation by the autonomic nervous system, mainly by unmyelinated sympathetic C fibers. To this end, various laboratory tests have been proposed, but the measurement of electrochemical skin conductance (ESC) by Sudoscan® is increasingly becoming the most widely used technique, because it allows a quick and simple assessment of the sudomotor function of the limb extremities. This technique is based on the principles of reverse iontophoresis and chronoamperometry and since its introduction in 2010, has been the source of nearly 200 publications. In the clinical field, most of these publications concern the evaluation of diabetic polyneuropathy, for which the value of Sudoscan® no longer needs to be demonstrated. However, there is also evidence for a role for Sudoscan® in the testing of the autonomic nervous system in various peripheral neuropathies of other origins or diseases primarily affecting the central nervous system. In this article, a comprehensive review of the literature on the clinical value of Sudoscan® outside of diabetes is presented, detailing ESC changes in neuropathies associated with various clinical conditions, such as hereditary amyloidosis or other genetic pathologies, chemotherapy neurotoxicity, dysimmune or infectious disorders, fibromyalgia, parkinsonism or other neurodegenerative diseases.

Sleep and wakefulness disturbances in Parkinson's disease: A meta-analysis on prevalence and clinical aspects of REM sleep behavior disorder, excessive daytime sleepiness and insomnia

Sleep disorders (SDs) are common non-motor symptoms of Parkinson's disease (PD) with wide variability in their prevalence rates. The etiology of SDs in PD is multifactorial because the degenerative processes underlying the disease and their interaction with drugs and clinical features may promote REM sleep behavior disorder (RBD), excessive daytime sleepiness (EDS) and insomnia. Therefore, we designed a meta-analytic study to provide a reliable estimate of the prevalence and associated clinical and neuropsychiatric aspects of SDs in PD. A systematic literature search was performed up to February 2022. Pooled RBD prevalence was 46%, and its occurrence was associated with older age, lower education, longer disease duration, higher levodopa equivalent daily dose (LEDD), worse motor and autonomic manifestations, poorer quality of life and autonomy, and more severe neuropsychiatric symptoms. The pooled prevalence of EDS was 35% and was associated with older age, longer disease duration, worse motor and autonomic symptoms, higher LEDD, reduced autonomy, and more severe neuropsychiatric symptoms. Insomnia was reported in 44% of PD patients and was related to longer disease duration, higher LEDD, and more severe depression. SDs are associated with a more severe PD clinical phenotype; further studies should explore the pathophysiological mechanisms underlying SDs and develop targeted therapeutic strategies.

Impact of rapid eye movement sleep behavior disorder and autonomic disorders on Parkinson's disease: a review

Parkinson's disease (PD) has heterogeneous clinical manifestations and prognoses. It is accompanied by a group of motor and non-motor symptoms ranging from independence to total disability, limiting work and personal care activities. Currently, disease subtype markers for informing prognosis remain elusive. However, some studies have reported an association between rapid eye movement (REM) sleep behavior disorder (RBD) and faster motor and non-motor symptom progression, including autonomic dysfunction and cognitive decline. Moreover, since autonomic dysfunction has been described in idiopathic forms of RBD, and they share some central regulatory pathways, it remains unclear whether they have a primary association or if they are more severe in patients with PD and RBD, and thus are a disease subtype marker. This article aimed at critically reviewing the literature on the controversies about the prevalence of RBD in PD, the higher incidence of PD non-motor symptoms associated with RBD, the evidence of faster motor worsening in parkinsonian patients with this parasomnia, and the main pathophysiological hypotheses that support these findings.

Autonomic dysfunction and phenoconversion in idiopathic REM sleep behavior disorder

BACKGROUND

REM sleep behavior disorder (RBD) is a common finding among patients with synucleinopathies. We aimed to determine the degree of autonomic dysfunction in patients presenting with idiopathic RBD (iRBD), and the predictive value of autonomic dysfunction for phenoconversion to a defined neurodegenerative disease.

METHODS

We searched our electronic medical record for patients diagnosed with iRBD who also underwent standardized autonomic function testing within 6 months of iRBD diagnosis, and who had clinical follow-up of at least 3 years following iRBD diagnosis. The composite autonomic severity score (CASS) was derived and compared between phenoconverters and non-converters using chi-square and Wilcoxon rank-sum tests.

RESULTS

We identified 18 patients who fulfilled inclusion and exclusion criteria. Average age at autonomic testing was 67 ± 6.6 years. Twelve (67%) patients phenoconverted during the follow-up period; six developed Parkinson's disease (PD), and the other six, dementia with Lewy bodies (DLB). Fifteen (83%) patients had at least mild autonomic dysfunction. There were no significant differences between overall converters and non-converters in total CASS or CASS subscores. However, iRBD patients who developed DLB had significantly higher total and cardiovagal CASS scores compared with those who developed PD (p < 0.05), and a trend for higher adrenergic CASS scores compared to those who developed PD and those who did not phenoconvert.

DISCUSSION

Autonomic dysfunction was seen in 83% of iRBD patients, and more severe baseline cardiovagal autonomic dysfunction in iRBD was associated with phenoconversion to DLB but not PD. Prospective studies are needed to confirm the value of autonomic testing for predicting phenoconversion and disease phenotype in iRBD.

Small fiber neuropathy and phosphorylated alpha-synuclein in the skin of E46K-SNCA mutation carriers

BACKGROUND AND OBJECTIVE

In 2004 we described the E46K mutation in alpha-synuclein gene (E46K-SNCA), a rare point mutation causing an aggressive Lewy body disease with early prominent non-motor features and small fiber denervation of myocardium. Considering the potential interest of the skin as a target for the development of biomarkers in Parkinson's Disease (PD), in this work we aimed to evaluate structural and functional integrity of small autonomic nerve fibers and phosphorylated alpha-synuclein (p-synuclein) deposition in the skin of E46K-SNCA carriers as compared to those observed in parkin gene mutation (PARK2) carriers and healthy controls.

PATIENTS AND METHODS

We studied 7 E46K-SNCA carriers (3 dementia with Lewy bodies, 2 pure autonomic failure, 1 PD and 1 asymptomatic), 2 PARK2 carriers and 2 healthy controls to quantify intraepidermal nerve fiber density and p-synuclein deposition with cervical skin punch biopsies (immunohistochemistry against anti PGP9.5/UCHL-1, TH and p-synuclein) and sudomotor function with electrochemical skin conductance (ESC) (SudoScan).

RESULTS

All E46K-SNCA carriers had moderate to severe p-synuclein deposits and small fiber neurodegeneration in different epidermal and dermal structures including nerve fascicles and glands, especially in carriers with Pure Autonomic Failure, while p-synuclein aggregates where absent in healthy controls and in one of two PARK2 carriers. The severity of the latter skin abnormalities in E46K-SNCA were correlated with sudomotor dysfunction (lower ESC) in hands (p = 0.035).

INTERPRETATION

These results together with our previous findings support the relevance of E46K-SNCA mutation as a suitable model to study small fiber neuropathy in Lewy body diseases.