Nonmotor features can differentiate Parkinson’s from essential tremor
Differences include nonmotor symptom severity, urinary symptoms, smell loss
People with tremor-dominant Parkinson’s disease experience a higher burden of nonmotor symptoms than people with essential tremor (ET), according to a recent report.
Overall nonmotor symptom severity, urinary symptoms, and loss of smell are among the factors that most clearly diverged between the two conditions.
Researchers believe the information can be used to help clinicians accurately diagnose these diseases, which often get confused with one another because they’re both characterized by the predominant motor symptom of tremors.
“As our understanding of these diseases deepens, future diagnostic criteria and treatment guidelines should more comprehensively consider the impact of NMS [nonmotor symptoms],” researchers wrote.
The study, “Nonmotor Symptoms Differ Between Essential Tremor and Tremor-Dominant Parkinson’s Disease,” was published in Brain and Behavior.
Tremors among most common motor symptoms of Parkinson’s
Tremors are involuntary muscle contractions that cause shaking or trembling body parts. They’re among the most common motor symptoms of Parkinson’s disease, where they usually appear as resting tremors — meaning they happen when the muscles are relaxed and still.
These involuntary movements are also the primary feature of ET, another progressive movement disorder. There, the more prevalent type of tremor is an action tremor, where the symptom occurs during voluntary movements.
Because of their overlap, it can be difficult for doctors to accurately diagnose these diseases based on motor symptoms. It becomes even more challenging when a person has tremor-dominant Parkinson’s, where tremor is the most prominent symptom relative to other common Parkinson’s motor issues that aren’t usually seen with ET.
A possible way to better distinguish Parkinson’s from ET is to look for differences in nonmotor symptoms, the array of symptoms unrelated to movement that are early and common features of Parkinson’s and which can also occur in ET.
In the study, scientists examined differences in nonmotor symptom profiles between tremor-dominant Parkinson’s and ET patients who were seen across centers in China. The analysis included 558 Parkinson’s patients, 584 ET patients, and a control group of 514 healthy adults.
Parkinson’s patients were older than those with ET and had been living with their disease for a shorter time, while ET patients were more likely to have a family history of the disease.
Tremors in Parkinson’s more often resting, asymmetrical, affecting lower limbs
Tremors in Parkinson’s patients were more often resting, asymmetrical (affecting one side of the body), and involving the lower limbs, while ET tremors were more often action, symmetrical, and affecting the head.
Nonmotor symptoms were evaluated with the Nonmotor Symptoms Scale (NMSS), where a higher score reflects more severe symptoms.
Total NMSS scores were significantly higher for both ET and Parkinson’s patients than for controls, and were also significantly higher in Parkinson’s patients than in those with ET, suggesting that Parkinson’s patients have the highest overall nonmotor symptom burden.
Parkinson’s patients also had significantly higher NMSS scores than both controls and ET patients across most specific symptom domains. Compared with the ET group, Parkinson’s patients had more severe symptoms in the domains of sleep/fatigue, mood/cognition, perceptual problems, gastrointestinal symptoms, urinary symptoms, and others.
The seven most frequently reported nonmotor symptoms were mood problems, urinary symptoms, fatigue, insomnia, constipation, loss of smell (hyposmia), and excessive sweating.
The Parkinson’s group most commonly experienced urinary symptoms (60.8%), fatigue (49.1%), and mood disturbances (47.5%). In ET, the most common symptoms were insomnia (42%), mood disturbances (34.8%), urinary symptoms (32.9%), and fatigue (31%).
People with Parkinson’s or ET at higher risk of common nonmotor symptoms
Generally, people with Parkinson’s or ET were at a higher risk of all seven of the common nonmotor symptoms compared to the control group.
Parkinson’s patients were also at a higher risk of all of those symptoms except insomnia relative to the ET group. The most notable difference was in smell loss, for which Parkinson’s patients were at a nearly eight times higher risk than ET patients.
Total NMSS scores, urinary symptoms, and smell loss were the factors that could most strongly distinguish Parkinson’s patients from the ET group. A statistical model combining these factors, along with family history, was the most accurate for differentiating the two diseases.
“Our research highlights the importance of considering NMS in the differential diagnosis of ET and PD-TD [tremor-dominant Parkinson’s],” the researchers wrote. “Identifying NMS … assists clinicians in making more accurate diagnoses, offering more personalized treatment options for patients.”
The researchers noted certain nonmotor symptoms, such as anxiety, depression, and REM sleep behavior disorder, are not captured in the NMSS and thus were not evaluated.
“Future studies should consider employing a longitudinal design and expanding the sample size to allow for a comprehensive assessment of NMS, further exploring the role of NMS in differentiating and managing ET and PD-TD,” the team concluded.
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