With Pierpaolo Turcano, MD
In early 2026, Rush will offer surface electromyography, an advanced, noninvasive diagnostic tool that objectively measures tremor frequency, amplitude and muscle activation patterns, to help clinicians distinguish Parkinson’s disease from other movement disorders and guide more precise, evidence-based treatment decisions.
Tremor is one of the defining features of Parkinson’s disease, but it shows up in a lot of other conditions — essential tremor, dystonia, even medication effects or functional movement disorders. Rest tremor, which we often think of as Parkinsonian, can actually occur in many people with essential tremor. That overlap is why only about half of patients get the right diagnosis in the first five years.
Surface EMG gives us an objective way to look under the hood. It measures things like tremor frequency, amplitude and muscle activation patterns. For example, Parkinson tremor tends to show an alternating pattern between agonist and antagonist muscles, while essential tremor or drug-induced tremor looks synchronous.
Dystonic tremor often shows a baseline co-contraction. In atypical parkinsonism, such as multiple system atrophy, tremor frequency is usually higher and more irregular. Those patterns help narrow the differential when the exam alone isn’t enough.
Some retrospective reviews found that electrophysiologic testing clarified the clinical diagnosis in about three-quarters of patients and identified functional tremor features in roughly a third. Among patients referred for medication-refractory essential tremor, about one in seven actually had a functional component. Identifying that ahead of time can prevent unnecessary invasive procedures such as deep brain stimulation or MR-guided focused ultrasound thalamotomy.
We look for variability in tremor frequency greater than 2 Hz, distractibility or entrainment during tapping tasks, and shifts in tremor direction or amplitude when the patient changes position. When those features dominate, the tremor is functional. When they coexist with a fixed-frequency pattern, it’s often a mix of functional and organic features.
Surface EMG complements the bedside exam. For tremor cases that don’t fit neatly into Parkinson’s, essential tremor or dystonia, EMG provides objective data that improves confidence, guides management, and in some cases, spares patients from invasive interventions.
