Parkinson's Disease

By Eshita Shah

Parkinson's disease is a movement disorder that is characterized by the progressive degeneration of dopaminergic neurons in the brain, particularly in a region known as the substantia nigra. This region is part of the basal ganglia, which is responsible for the initiation, coordination, and overall control of movement. As the disease progresses, the lack of dopamine in the brain leads to loss of control over voluntary movements, causing symptoms such as tremor, bradykinesia, and rigidity in muscles. Non-motor symptoms of Parkinson's include depression and loss of smell.

Parkinson's disease affects nearly 6 million people worldwide, with 50,000-60,000 new cases in the United States alone per year. The disease is more common in men than women, reasons for which are unknown. The onset of Parkinson's is idiopathic, meaning the cause of the disorder is unknown; however, it is known that the Lewy Bodies that aggregate in dopaminergic neurons are composed primarily of alpha-synuclein. It is likely that these proteins are causing neuronal death in the substantia nigra.

While there is no cure for Parkinson's as of yet, there are various treatments available. The most common and effective drug therapy is a combination of carbidopa and levidopa; levidopa is a precursor of dopamine, so upon crossing the blood brain barrier, the drug is converted into dopamine and is able to make up for the lack of dopamine (to an extent). The neurosurgical approach to treating Parkinson's is known as Deep Brain Stimulation (DBS). DBS is a procedure in which an electrical stimulator and electrode are implanted in a patient, through which brief electrical pulses are sent to a specifically targeted region of the patient's brain. This method has been used widely to successfully reduce Parkinson's symptoms such as tremor and bradykinesia. The most common targets have been the ventral thalamic nuclei as well as the globus pallidus; however, more recently, stimulation of the subthalamic nucleus has yielded great results.

The mechanism of DBS is fascinating; the electrical stimulator inhibits the abnormal neural transmission that causes the motor dysfunctions in Parkinson's and overrides those signals with a "normal" electrical signal, diminishing Parkinson's symptoms. The effectiveness of the DBS device can be seen through both voluntary movements and tremors of the patients, and adjustments are made in terms of the frequency and amplitude of the signals being produced by the device. Very recently, doctors at Stanford University implanted a new type of DBS device in a patient. This device not only stimulated the subthalamic nucleus, but was able to detect and record the electrical output of the region. A clear benefit of this type of device is a more direct measurement of the effectiveness of the device, allowing for more accurate adjustments to be made based on the patient's unique response to the treatment. A previous study published by the Cleveland Clinic in Ohio demonstrated that DBS could be used in patients with depression and OCD. With further understanding of the mechanisms of DBS, hopefully it can be applied to treat patients with a variety of disorders, not just Parkinson's disease.