Q: Can Parkinson’s disease cause dementia?

A: Parkinson’s disease (PD) was first described in 1817 by Dr. James Parkinson who was evaluating patients with a progressive motor system neurological disorder, but as noted below there are many possible non-motor system manifestations of PD and this includes dementia. Today there are over a million Americans living with this PD, and 60,000 more are diagnosed every year. PD affects four per 100 people over age 50, and men have a 1.5 times higher risk than women.

The loss of certain cells certain cells in the brain (and possibly elsewhere in the body) and development of Lewy Bodies (abnormal collections of the protein alpha-synuclein) are noted to occur in PD patients. However, the specific cause of these findings, and whether there are other pathophysiological aspects of the disease, is not well understood.

PD is usually thought of as a neurodegenerative disease affecting the patient’s motor system with the cardinal symptoms of:


Bradykinesia (slow movement) or akinesia (loss of movement)
Rigidity of the muscles (often evaluated on physical exam by noting a ‘cogwheel-like’ motion as the clinician moves the patient’s limb)
Resting tremor (typically of the hands which is usually 4 to 6 beats per second and which usually improves with volitional movement; it is often described as a ‘pill rolling’ motion of the hands) that often starts as a subtle symptom and becomes more obvious as the disease progresses
Instability upon standing (this usually does not manifest until later in the course of the disease).

However, PD may manifest with many other motor symptoms, such as:


Tremor involving the legs, lips, jaw and even the tongue
Involvement of the eyes, face (sometimes described as ‘mask-like’) and/or head
Gait abnormalities.

Non-motor symptoms of PD may include:


Neuropsychiatric conditions (up to 50 percent have depression, a third have anxiety, and many have others neuropsychiatric conditions such as psychosis or hallucinations)
Dementia (eventually affecting up to 40 percent of patients)
Other cognitive deficits
Loss of the sense of smell
Sleep disturbances
Other symptoms.

There is no specific test for PD, although a single photon emission computed tomography imaging test (SPECT scan) using a specialized radiotracer can help make the diagnosis when it is uncertain. Many patients with suspected PD will have a magnetic resonance imaging (MRI) scan done to rule out other possible causes of their symptoms. The diagnosis of PD is made based on the clinical symptoms and the physical examination.

The diagnosis of PD relies on the presence of bradykinesia in addition to a rest tremor or muscle rigidity. The presence of other criteria (such as significant improvement when dopaminergic medications are started, and/or certain other PD symptoms as noted above) supports the diagnosis. Certain ‘red flags’ make a diagnosis of PD much less likely. Most of these ‘red flags’ involve a progression of certain types of symptoms that are more rapid than expected with PD, or the absence of certain symptoms after a specified period of time during which patients with PD would usually have them. Finally, other causes of the patient’s symptoms should be considered (for example Essential Tremor, Dementia with Lewy bodies, many other conditions) and determined to be less likely than PD.

There is presently no cure for PD. Medications can help minimize the symptoms, although as the disease progresses over time increasing doses of medications, additional medications, and even specialized surgical treatments may be required. The surgical treatments for PD include deep brain stimulation (DBS, where an electrode is inserted into a specific area of the brain and an impulse generator utilized to send electrical signals) and surgically implanting a tube through the stomach into the small intestines to deliver a gel form of a certain PD medication.

There are several new medications being developed to treat PD. There is even some early research showing a medication usually used to treat type 2 diabetes might slow progression of the disease. Other therapies, for example MRI guided focused ultrasound (which uses ultrasound energy under MRI guidance to ablate a small area in the brain, and which has been shown to be useful in some patients with Essential Tremor), are being evaluated for PD.

Jeff Hersh, Ph.D., M.D., can be reached at DrHersh@juno.com