Parkinson's Disease: Its Over-Diagnosis and Under-Diagnosis

In this era of genuinely marvelous, high-tech, medical devices, it is sometimes surprising that certain diseases are still diagnosed "clinically," meaning that the clinician makes the call based on just the story of symptoms and the physical exam. Parkinson's disease is one such disease. There is no "Parkinson scan" or "Parkinson blood-test" to rely upon. MRI scans, CT scans and blood tests are usually normal in people with this disease.

Of course, once upon a time—before scans and blood-tests even existed—this is how all diagnoses were made. So, in a sense, diagnosing Parkinson's disease gets back to the very roots of what doctors are supposed to do. But when there are no corroborative tests available to prove or disprove a diagnosis, even the doctor sometimes gets it wrong.

Before delving into the challenges of diagnosing Parkinson's disease, let's first consider what is known about this condition.In 1817 James Parkinson, an English surgeon and apothecary, published a classic, short book entitled "An Essay on the Shaking Palsy." In it, Parkinson identified a consistent pattern of physical abnormalities in six patients he had examined. Although people with identical abnormalities had doubtlessly been around for thousands of years, Parkinson was the first to recognize this pattern of abnormalities as a distinct condition. For this important achievement, the disease was eventually named for him.

In the book's opening sentence Parkinson wasted no time in laying out prominent features of this disease: "Involuntary tremulous motion, with lessened muscular power, in parts [of the body] not in action and even when supported; with a propensity to bend the trunk forwards, and to pass from a walking to a running pace: the senses and intellects being uninjured."

Subsequently, scientists discovered that degeneration of a limited group of brain cells containing the chemical transmitter dopamine was responsible for these clinical changes. (The group of brain cells involved is too slight to show up on brain scans in all but the most advanced of cases.) In 1967, levodopa (one of two ingredients in brand-name Sinemet) a drug the body can convert into dopamine, was found helpful in alleviating many of the symptoms. Later, other drugs (dopamine agonists) were created that improved symptoms by mimicking the action of the missing dopamine. These include bromocriptine (brand name Parlodel), pergolide (Permax), pramipexole (Mirapex) and ropinirole (Requip). To date, there are no treatments that reliably stop or reverse the underlying disease-process.

As a condition that affects about one percent of people over the age of 60, Parkinson's disease is usually on the radar screen of patients and doctors alike when new symptoms are present that suggest the disease. That other conditions can resemble it was not news to James Parkinson who devoted a chapter of his 1817 book to "Shaking palsy distinguished from other diseases with which it may be confounded."In my consultation practice of neurology, I see both over-diagnosis and under-diagnosis of Parkinson's disease. The problem usually centers on one of the most visible of symptoms, the tremor. When tremor of the hands is present, doctors often diagnose Parkinson's disease, even when another condition is to blame. When tremor is absent, doctors often fail to consider Parkinson's disease, even when it is present. One key to accurate diagnosis is to focus on the characteristics of the tremor itself. The Parkinsonian tremor usually affects one hand first, and at all stages of the disease the initially affected hand remains more tremulous than the other hand. And, as Parkinson himself emphasized, the tremor is most evident when the hand is at rest or supported, and decreases when the hand is in the air or put to use. In other conditions that cause hand-tremors, the hands are more equally affected, and the tremor is more evident when the hands are in the air or put to use.

What about cases in which no tremor is present? Because symptoms of Parkinson's disease worsen slowly—year by year instead of month by month—patients and their families often mistake these changes as due to normal, healthy aging. Non-tremor symptoms of Parkinson's disease can include relative immobility of body-parts (hypokinesia), especially of the face which can show a mask-like lack of expression. Movements, once initiated, are slow (bradykinesia). Walking, as James Parkinson noted, involves a bent-forward posture with shuffling, short steps and reduced swinging of the arms. Sometimes the body's center of gravity gets ahead of the feet's ability to catch up, resulting in the passing "from a walking to a running pace" that Parkinson described and is known as festination.

The physical exam also shows clumsiness in hands and feet. Increased muscle tone, called "rigidity," is encountered in the patient's neck and arm muscles, even while they are supposed to be relaxed.

Patients who have Parkinson's disease without tremor are often the most gratifying cases to treat. Having developed their problems slowly and having believed all along that their symptoms were due to aging, they are happily astonished by the rapid improvement in function produced by appropriate medication.

(C) 2005 by Gary Cordingley