Parkinson's Disease Tests

Parkinson's disease is a clinical diagnosis. No lab tests or imaging procedures can definitively confirm a diagnosis of Parkinson's; instead, a neurologist will make a judgment based on a complete medical history and a period of observation, during which it becomes clear exactly what symptoms are present and how they respond to treatment. Misdiagnosis remains an important issue. Postmortem examinations demonstrate that approximately 20 percent of patients with a diagnosis of Parkinson's actually have other disorders that mimic it.

A fairly common form of tremor known as essential tremor, for example, is often confused with the resting tremor of Parkinson's. However, essential tremor is an action tremor (brought on by movement) rather than a resting tremor. Furthermore, there is no associated rigidity, gait disturbance, or facial masking with the essential tremor.

In evaluating a patient with possible Parkinson's disease, the physician will take a careful history that includes a description of symptom development, family history, history of exposure to pesticides or toxins, and other medical conditions and medications. Any imaging such as MRIs will be reviewed. The patient will undergo a neurological exam and specifically an exam that looks at possible symptoms of Parkinson's. This includes rating a tremor as to whether it is a resting tremor, listening to the patient's voice, rating speed and amplitude of hand and leg movements, and checking the patient's gait and balance. Rating scales that are used to evaluate the extent of motor impairment include the Columbia University Rating Scale, the Northwestern University Disability Scale, and—most commonly—the Unified PD Rating Scale.

Another part of the examination may include what is called a Sinemet challenge—the Parkinson's medication Sinemet is given to the patient to see if the symptoms are improved. A significant improvement following the administration of medication often confirms the diagnosis, since a complete lack of response to these agents is rare in patients who truly are affected.

Clinical assessment is sensitive in detecting symptomatic Parkinson's, but it cannot detect preclinical disease. Functional imaging with positron emission tomography and single photon emission computed tomograhy provides a method for detecting preclinical changes in brain function. Numerous PET and SPECT tracers are capable of differentiating patients with Parkinson's from normal subjects. These may be useful tools for both preclinical diagnosis and monitoring of disease progression, but they are expensive and not widely available.