Study acquits drug of causing havoc
By Edward Edelson
HealthSCOUT Reporter
TUESDAY, Sept. 5 (HealthSCOUT) -- Parkinson's disease can affect nerves in the heart as well as the central nervous system, a finding that federal researchers say can affect how the condition is diagnosed and treated. The same kind of nerve damage in the brain that causes the trembling, slow body movements and rigid limbs of Parkinson's disease has been found in the heart and probably affects nerves elsewhere in the body, reports a group led by Dr. David S. Goldstein, chief of clinical neurocardiology at the National Institute of Neurological Disorders and Stroke (NINDS), in today's issue of the Annals of Internal Medicine.
The study looked for damaged heart nerves because of a longstanding issue in the treatment of the disease, says Goldstein. The standard medication is levodopa, "often a miraculous drug that emphatically reverses movement problems," he says. But many patients given the drug experience orthostatic hypotension, a severe drop in blood pressure that can make them faint when the stand up. Doctors have wondered whether the blood pressure problem is caused by the drug or the disease.
So the NINDS researchers began a study that included patients with Parkinson's disease and other nervous system problems associated with orthostatic hypotension. They looked mostly at the sympathetic nervous system, which controls many automatic functions of body organs.
Levodopa not to blame
So imaging tests "may help distinguish Parkinson's disease from similar conditions in which blood pressure decreases on standing," Goldstein says. And when a Parkinson's patient has orthostatic hypotension, the study shows that the underlying nerve problem, not levodopa, is the cause, and that can help determine how the patient is treated, he says. "This study says that the hypotension comes not from the drug treatment. It comes from the loss of sympathetic nerve terminals in the heart and elsewhere. If you recognize that it comes from sympathetic nerve failure, you can be straightforward in coming up with a treatment that helps the patient," Goldstein says.
The finding could definitely affect treatment, says Dr. Louis H. Weimer, assistant professor of neurology at Columbia University College of Physicians and Surgeons. "A lot of the drop in blood pressure has been blamed on levodopa. This may lessen the hesitance of doctors to use it," he says. It also can help diagnose the condition, he says. Because Parkinson's disease resembles multiple-system atrophy, "there may be quite a number of people who are said to have Parkinson's disease who actually have multiple-system atrophy." The new study helps outline "some clear clinical differences," he says. The finding gives some valuable basic information about the kind of damage done to specific nerves in specific centers of Parkinson's patients, says Goldstein: "What is enticing about this report is the suggestion that Parkinson's disease results from a process which in the brain leads to destruction of dopamine cells in the corpus striata [two regions of the brain] and which also destroys norepinephrine cells in the heart. They are both catecholamines. So maybe Parkinson's disease is a disease of the catecholamine system, not just these brain cells." He says neurologists can follow that lead in research that could produce better treatment of the disease.
What To Do
Patients with Parkinson's disease whose doctors have been reluctant to prescribe levodopa because of orthostatic hypotension can now take the medication without fear the drug causes that problem.