Parkinson's disease and Huntington's disease, we all know them as movement disorders with uncontrolled movements such as trembling and shaking as the most prominent symptoms. Therefore, the treatment of these diseases is mainly focused on these motor symptoms.

In fact, Parkinson's disease was initially seen as a neurological disorder. In the 1990s, however, it became known that psychiatric symptoms are also common in these patients. One of these complaints is depression. In 2003, for his own doctorate, Prof. Dr. Leentjens conducted research into the validity of depression scales in parkinsonian patients, among other things. It turned out that the cut-off points in these scales were not valid because of the overlapping symptoms in depression and Parkinson's disease.

As a result of this research and others, the Movement Disorder Society began a program to validate numerous measurement scales for use in Parkinson's disease, including psychiatric scales for not only depression, but also apathy, anxiety and hallucinations.

Slowly, a paradigm shift occurred in which movement disorders were no longer seen as neurological, but neuropsychiatric disorders. Such disorders require a multidimensional and multidisciplinary approach, according to Leentjens.

Machine learning

In addition to research on Parkinson's disease, Leentjens has since then extended his research to Huntington's disease and Tourette's syndrome. To better understand the complicated relationship between psychiatric and neurological symptoms, he proposes ecological momentary assessments. This involves taking measurements through an app.

Each day the patient fills out a questionnaire several times on both motor and psychiatric symptoms, revealing fluctuations in symptoms and interrelationships between them. A report of this is sent to the treating physician, allowing him to better tailor treatment to the patient's individual situation.

The use of "machine learning" techniques can also shed more light on complex relationships between symptoms. Research into the possibility of predicting disease course with this technique is already underway in Huntington's disease, and application will be extended to Parkinson's and Alzheimer's disease.

Deep Brain Stimulation

In addition to this research, Prof. Dr. Leentjens also works clinically as a psychiatrist within the care line of deep brain stimulation (DBS). DBS is applied within psychiatry at the Maastricht University Hospital (MUMC+) in compulsive disorders and on an experimental basis also in tourette patients. For the latter indication, the MUMC is the only institution in the Netherlands.