By Daniel Martínez
Popular Science Article

Parkinson’s disease is a neurodegenerative disorder affecting more than 4 million people around the world, and the number is expected to triple by 2030. Patients with Parkinson’s disease suffer from a wide variety of motor symptoms, such as tremor, stiffness, and slowness of movement, as well as non-motor symptoms, such as memory difficulties, depression, constipation, and sleep problems, among others. Overall, there are two subtypes of Parkinson’s disease, with some patients exhibiting tremor as the predominant symptom (TD) and others developing greater slowness of movement, stiffness, and gait difficulty (PIGD).

Parkinson’s disease is believed to have a more benign course in patients with tremor as the predominant symptom (TD). However, this is not true. Patients with the tremor-dominant subtype also experience some non-motor problems and, according to our observations, their disease tends to progress to other motor subtypes of Parkinson’s disease.

That’s why we set out to investigate whether the features of motor symptoms in patients with Parkinson’s disease remained the same or changed during 20 years of follow up.

Method

The first step was to conduct a statistical analysis using an artificial intelligence technique called clustering. Following our analysis of patient symptoms, several motor subtypes of Parkinson’s disease emerged: a type with tremor as the predominant symptom (TD), another type with slowness of movement, stiffness, and gait difficulty as predominant symptoms (PIGD), and an intermediate type. We applied this method again in two different populations, getting the same results. Then, we set out to follow patients for several years and analyze their data with the same method to find out what would happen.

Changes in Parkinson’s Disease Subtypes

Based on our study results, we identified two main populations: while most patients (88%) shifted motor subtype category over time, a minority of individuals remained within the same subtype category. Of the patients who shifted motor subtype category, 50.5% had been classified as TD and 38.6% as PIGD upon diagnosis. After the 20-year follow-up period, these numbers had changed: 20% of patients were classified as TD and 73.8%, as PIGD. We also noted a gradual decrease in the proportion of TD patients and an increase in the proportion of PIGD patients.

Disease Progression

Of the patients who maintained a stable motor subtype designation (11.6%), those diagnosed with the TD subtype at the start (tremor as the main symptom) experienced worsening of symptoms over 20 years. The same was found for patients with the PIGD subtype (slowness of movement, stiffness, and gait difficulty as predominant symptoms) as people who developed PIGD over time also experienced worsening of symptoms and the corresponding clinical difficulties.

Results

Based on our findings, we can conclude that the study method may be applied reproducibly to identify the motor subtypes of Parkinson’s disease. Besides, these results suggest that the motor symptoms of Parkinson’s disease do change over time in the majority of cases, progressing to the PIGD subtype.

Being able to identify patients who will progress to a slightly more complicated form of Parkinson’s disease, such as the PIGD subtype, will help us study and implement strategies to study disease modifiers and tailor treatment.

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About the author
Dr. Daniel Martínez Ramírez
is a research professor at the Tecnológico de Monterrey School of Medicine and Life Sciences. He received his M.D. from Universidad Autónoma de Nuevo León and completed his residency in Neurology at Tecnológico de Monterrey. He pursued fellowship training at the University of Florida and at Mexico’s National Institute of Neurology and Neurosurgery, where he completed the Parkison’s Disease and Movement Disorders Fellowship Program. Dr. Martínez-Ramírez has over 120 publications, which include research papers and presentations at national and international conferences. He co-authored the book “10 Secretos en Parkinson”, an Amazon bestseller. He is a member of the National System of Researchers (Level 2) and Mexico’s National Academy of Medicine. daniel.martinez-ramirez@tec.mx

Do you want to learn more?

Read the research paper:
Parkinson’s disease motor subtype changes during 20 years of follow-up, by Dr. Daniel Martínez, published this year in the scientific journal Parkinsonism & Related Disorders.

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