Analysis of Cutaneous Phosphorylated Alpha-Synuclein to Identify Patients at Risk of Progressing From Essential Tremor to Parkinson's Disease

Inclusion Criteria:

* Age 50-85 years old
* Diagnosis of ET as defined by the 2018 MDS Task force paper "1) isolated tremor syndrome of bilateral upper limb action tremor 2) at least 3 years' duration 3) with or without tremor in other locations (e.g., head, voice, or lower limbs) 4) absence of other neurological signs, such as dystonia, ataxia, or parkinsonism." OR
* Diagnosis of ET-Plus as stated by the 2018 MDS Task force paper, "Tremor with the characteristics of ET and additional neurological signs of uncertain significance such as impaired tandem gait, questionable dystonic posturing, memory impairment, or other mild neurologic signs of unknown significance that do not suffice to make an additional syndrome classification or diagnosis. ET with tremor at rest should be classified here."
* Willing to participate in all study procedures
* Able and willing to provide written informed consent

Exclusion Criteria:

* Under age 50, Over age 85
* Clinical evidence of severe peripheral vascular disease
* Clinically active coronary artery or cerebrovascular disease
* Participant is currently on anticoagulant or dual anti-platelet therapy
* Alcoholism
* Allergic reaction to local anesthesia
* History of or increased risk for impaired wound healing, scarring, or keloid formation
* Diagnosis of ET or ET-Plus that is clinically determined to likely be secondary to brain injury or vascular compromise
* History of other neurodegenerative disorder or evidence of neurological co-pathology
* Abnormal DaTscan
* Participant is currently receiving treatment with carbidopa-levodopa for PD
* Isolated focal tremors (head, voice)
* Task-specific tremor (e.g., primary writing tremor)
* Position-specific tremors that does not otherwise meet clinical diagnostic criteria for ET
* Sudden onset and step-wise deterioration
* Prior to enrollment, receipt of an intracranial procedure intended to treat tremor or parkinsonism, including thalamic deep brain stimulation (DBS) implantation or focused ultrasound (FUS) thalamotomy. Other prior intracranial surgery is exclusionary only when, in the investigator's or Sponsor's Chief Medical Officer's judgment, it could materially affect motor assessments, diagnostic classification, participant safety, or interpretation of study outcomes.