Understanding Parkinson’s Disease

90,000 new cases are diagnosed every year in the U.S.; the average age at diagnosis: 70 years

By Eva Briggs, M.D.

 

Parkinson’s disease affects about one million people in the U.S., and about 90,000 new cases are diagnosed every year.

It’s a degenerative neurological disease that is more common in older individuals. The average age at diagnosis is 70 years. But there is no blood test or imaging study to tell whether a person has Parkinson’s. So it is a clinical diagnosis.

The disease is named for a doctor named James Parkinson who published a detailed description in 1817.

If there is no simple test, you are probably wondering how does a doctor know that a person has Parkinson’s? This article explores the clinical features of this illness.

First, Parkinson’s is a motor (movement) disorder. It is progressive, worsening over time. It is secondary to a deficiency of the neurotransmitter dopamine in a brain region called the substancia nigra. When dopamine levels are low, it requires greater effort to move the body. Most cases are idiopathic, meaning we really don’t know why it happens. Some cases are secondary to brain injury, drug induced such as prolonged use of certain antipsychotics or exposure to pesticides such as Agent Orange.

The motor symptoms can be thought of as the four S’s: shaky, slow, stiff and stumbling.

Shaky refers to a resting tremor. It goes away during sleep and voluntary movement. Tremor is common in idiopathic Parkinson’s. It typically starts in one arm or leg, eventually progressing to affect both sides of the body. The tremor resembles pill rolling or foot tapping. Tremor is rare in drug-induced Parkinson’s.

Slow movements are technically called bradykinesia. This can be disabling early on. Bradykinesia affects fine motor tasks such as dressing. It can cause handwriting to become small, known as micrographia. Patients may appear to be staring all the time because of a decreased blink rate.

Stiff indicates rigidity caused by increased muscle tone.

Stumble refers to balance problems causing falls. These gait problems include decreased arm swing and retropulsion, the inability to stop. Parkinson’s patients often have rapid shuffling steps while leaning forward.

Although considered a motor disorder, some nonmotor symptoms can appear years before the movement difficulties begin. These include insomnia, disorders of smell, sleep problems, speech difficulties, disorders of mood and memory troubles.

Parkinson’s can affect the autonomic nervous system leading to orthostatic hypotension (low blood pressure when standing up), excessive sweating, urinary incontinence, altered sexual function, constipation and double vision.

When the clinical picture fits, there is no definitive test. Technically a brain biopsy would confirm the diagnosis but that’s too invasive for practical use. MRI can exclude conditions that might mimic Parkinson’s such as a basal ganglia stroke.

The symptoms of Parkinson’s disease don’t develop until 65% of the dopamine producing neurons are lost. From there a typical course is the pre-motor symptoms (mood, sleep, smell, etc.) described above. This phase lasts about two to five years. The motor symptom phase (shaky, slow, stiff, stumbling) gradually worsens with time. Later symptoms can include more falls, cognitive issues and communication problems. The disease is often fatal about 15 years after diagnosis.

There are medications and procedures to treat Parkinson’s. Because the timing of when to start treatment with which drug is nuanced, it’s beyond the scope of this article.