Transcranial direct current stimulation helps with Parkinson’s disease-related pain

A study in Spain has found that transcranial direct current stimulation (tDCS) can alleviate certain aspects of Parkinson’s disease-related pain. The benefit was observed after ten 20-minute sessions, where a 2mA current was applied over the primary motor cortex on the side of the brain opposite the pain. The findings were published in Clinical Neurophysiology.

Parkinson’s disease is a progressive neurological disorder that primarily affects movement. It develops due to the degeneration of nerve cells in the part of the brain called the substantia nigra, which produces the neurotransmitter dopamine. The decrease in dopamine levels leads to abnormal brain activity, resulting in impaired movement and other symptoms.

Common symptoms of Parkinson’s include tremors, stiffness, and balance and coordination difficulties. As the disease progresses, it affects speech, writing, and other fine motor skills. Non-motor symptoms may include sleep disturbances, sensory changes, emotional fluctuations, and cognitive decline. Pain in Parkinson’s disease typically arises from muscle stiffness and rigidity, as well as the abnormal postures that often develop, contributing to considerable muscular discomfort.

Study author Yeray González-Zamorano and his colleagues wanted to assess whether tDCS over the primary motor cortex region of the brain could be used to alleviate pain related to Parkinson’s disease. The primary motor cortex is a region of the brain located in the frontal lobe, responsible for generating neural impulses that control the execution of movement.

Transcranial direct current stimulation is a non-invasive technique that modulates neuronal activity by delivering a low-intensity electrical current through electrodes placed on the scalp. The goal of tDCS is to enhance or inhibit brain activity.

The study included 22 individuals with Parkinson’s disease who were experiencing pain related to the condition. They were recruited from an outpatient clinic in Madrid, Spain.

Participants were randomly assigned to either receive actual tDCS or a placebo (sham) stimulation. Each group underwent ten 20-minute sessions, with the setup visible to participants. In the real stimulation group, electricity was activated, while in the sham group, it was only on for the initial 30 seconds to mimic the sensation of stimulation. Participants were aware that they might receive the sham treatment but could not ascertain their actual group.

The therapist, unaware of the treatment type, activated the stimulation by entering a code that initiated either the actual or sham procedure, ensuring any observed effects were due to the stimulation rather than psychological influences.

Before treatment, two days after completing the treatment, and 15 days later, a trained physical therapist evaluated the patients. Assessments of depression, anxiety, movement-related pain fear, and catastrophizing thinking were conducted at the beginning. Pain assessments included the King’s Parkinson’s disease Pain Scale, Brief Pain Inventory, widespread mechanical hyperalgesia assessment, temporal summation task, and conditioned pain modulation task.

Results indicated that the active treatment group showed improvement in specific pain indicators 15 days post-treatment, which were less pronounced two days after treatment ended. Improvements were notable in fluctuation-related pain, nocturnal pain, and discoloration/edema/swelling.

Conditioned pain modulation, which reduces pain perception in one area when a second pain stimulus is applied elsewhere, also improved in the active group. This finding suggests enhanced central nervous system function in regulating pain. Additionally, the treatment ameliorated symptoms of widespread mechanical hyperalgesia, indicating reduced sensitivity to pain from mechanical sources like pressure or touch.

“We found that tDCS over M1 [primary motor cortex region of the brain] effectively reduced clinical perceived pain, improved WMH [widespread mechanical hyperalgesia] and enhanced CPM [conditioned pain modulation] compared to sham stimulation. However, tDCS did not significantly improve overall pain intensity, pain interference nor TS [temporal summation i.e., repeated stimulation of the same intensity increasing the perceived intensity of pain over time). Interestingly, improvements in PD-pain and WMH were observed after 15 days of treatment, while CPM enhancement was immediate and sustained,” the study authors concluded.

The study sheds light on the effects of tDCS on Parkinson’s disease-related pain. However, it should be noted that the number of study participants was very small. Because of that, even quite substantial effects could easily have gone unnoticed as they could not be differentiated from random variations in data with sufficient confidence.

The paper, “TDCS for Parkinson´s disease-related pain: a randomized trial,” was authored by Yeray González-Zamorano, Francisco José Sánchez-Cuesta, Marcos Moreno-Verdú, Aida Arroyo-Ferrer, Josué Fernández-Carnero, K. Ray Chaudhuri, Anna Fieldwalker, and Juan Pablo Romero.