One of the distinctive features of Parkinson's disease is muscle rigidity, a pathological increase in muscle tone manifested by sustained and involuntary contraction, which constitutes a disabling limitation of mobility, sometimes associated with chronic pain. To date, the mechanisms underlying this phenomenon, for which no reliable instrumental measurement is available, are still unclear.

An international study, coordinated by Sapienza in collaboration with University College London and the National Institutes of Health (NIH), Bethesda (USA), introduces a new interpretative hypothesis according to which stiffness is linked to the dysfunction of a specific neural circuit that includes functional connections between the spinal cord, cerebellum and the reticular formation of the brainstem.

The paper, which clarifies relevant pathophysiological aspects of rigidity and also addresses the problem of the experimental study of this clinical sign, was published in the journal Brain.

Thanks to a novel experimental protocol using innovative robotic instrumentation, combined and synchronised with specific neurophysiological and biomechanical measurements, researchers could use an algorithm to assess muscle characteristics and reflex nerve activity of 20 patients with Parkinson's disease and 25 healthy control subjects with similar age and anthropometric characteristics.

"The main scientific achievement of our study," says Antonio Suppa of the Department of Human Neuroscience of Sapienza University of Rome, "consists in the experimental demonstration that stiffness in Parkinson's disease depends on specific alterations in the nervous control of muscle tone (e.g. speed-dependent increase in long latency reflexes) that in turn reflect a dysfunction in the connections between the spinal cord, cerebellum and the reticular formation of the brainstem."

Parkinson's disease is a neurodegenerative pathology that is very frequent in the general population (about 300,000 patients in Italy) and, unfortunately, is constantly growing, according to the latest estimates of the World Health Organisation. More in-depth knowledge of its main clinical signs and symptoms is essential, also with a view to more appropriate planning and programming of specific public health interventions.

References:

Rigidity in Parkinson’s disease: Evidence from Biomechanical and Neurophysiological Measures, Francesco Asci, Marco Falletti, Alessandro Zampogna, Martina Patera, Mark Hallett,John Rothwell, e Antonio Suppa,  https://doi.org/10.1093/brain/awad114

Further Information

Antonio Suppa
Department of Human Neuroscience
antonio.suppa@uniroma1.it