Deep Brain Stimulation Improves Olfactory Symptoms in Parkinson's Disease Patients Better than Medication

Newswise — It is estimated that 60,000 new cases of Parkinson's disease (PD) are diagnosed each year, adding to the estimated one to 1.5 million Americans who currently have the disease. The latest epidemiology studies indicate that by 2030, 8.7 million people worldwide will be affected by the disease. There were an estimated 19,660 PD-related deaths in the United States in 2006.

Early in the disease, there is a loss of brain cells that produce the chemical dopamine. Normally, dopamine operates in a delicate balance with other neurotransmitters to help coordinate the millions of nerve and muscle cells involved in movement. Without enough dopamine, this balance is disrupted, resulting in tremor (trembling in the hands, arms, legs and jaw); rigidity (stiffness of the limbs); slowness of movement; and impaired balance and coordination " the hallmark symptoms of PD. One early sign of PD is the loss of the sense of smell (dysosmia), which often occurs prior to any abnormal movements. The exact reason for this loss is still under investigation, although it may be due to the loss of the brain cells that are used to sense and/or process odors.

Researchers at the University of Massachusetts Medical School investigated the effects of deep brain stimulation (DBS) on PD patients suffering from dysosmia. The results of this study, DBS-implanted Parkinson's Disease Patients Show Better Olfaction Than Those Treated Medically, will be presented by Mary Linton B. Peters, MS, 4:21 to 4:30 p.m. on Wednesday, May 6, 2009, during the 77th Annual Meeting of the American Association of Neurological Surgeons in San Diego. Co-authors are Julie G. Pilitsis, MD, PhD, Sathish Kumar Dundamadappa, MD, Jean King, PhD, Peter Novak, MD, PhD, Paula Ravin, MD, and Joan Swearer, PhD.

DBS is an accepted treatment for advanced PD. DBS involves the placement of small electrodes into deep brain structures for the treatment of a variety of neurological disorders. The electrodes are connected via wires to a battery that is placed in the chest wall. Everything is under the skin, but may be adjusted with a magnet outside the body. The system functions much like a pacemaker for the heart. However, DBS is presumed to help modulate abnormal brain activity, so that the brain can function more effectively. DBS has several advantages over other neurosurgical procedures because it does not damage brain tissue and it may be regulated in the clinic setting, requiring only short sessions.

A recent study (JAMA, 7 Jan 2009) showed that DBS was more effective than medical therapy for controlling PD in patients with advanced disease, although as may be expected, there were greater adverse side effects associated with surgery than medication. "Two prior studies suggested that DBS patients have improved odor discrimination in stimulation-on state. However, it is unclear whether this improvement was treatment related or secondary to stimulation effects," stated Ms. Peters.

Of the 45 PD patients enrolled in this study, 9 had bilateral subthalamic nucleus (STN) DBS and 36 were medically treated. The 45 patients' scores were compared to those of 44 healthy people of the same age and gender. Patients were tested in stimulation on/medication on-state and medication-on-state respectively. Olfactory testing was done via the University of Pennsylvania Smell Identification Test (UPSIT), in conjunction with a battery of psychological tests. The following results were noted:

"¢The subset analysis of PD patients with and without DBS placement revealed no difference in apathy (Apathy Evaluation Scale), depression (Beck Depression Inventory), and nonmotor symptoms (UK PD Society questionnaire).

"¢DBS patients were significantly younger, however intergroup differences in UPSIT scores exceeded those seen in the control group with similar ages.

"¢Patients receiving high versus lower medication doses showed no olfactory difference.

"¢DBS patients exhibited better olfaction on UPSIT (p<0.05).

"¢No difference was noted in Hoehn and Yahr status, gender, smoking status, medication dosing, or maximal olfactory sulcus depth on MRI.

As expected, PD patients had impaired performance compared to patients without PD. The difference between the groups on each survey was statistically significant, and the results for sense of smell were the most dramatic. These findings, however, do not mean that individuals with a poor sense of smell are at greater risk for PD.

"This study provides further evidence that PD patients treated with DBS have improved olfaction. It also may suggest that DBS with medication improves dysosmia to a greater extent than medication alone. The combination of the neurologist's clinical suspicion with sense of smell and apathy surveys has potential as a screening tool that could aid in earlier and more accurate diagnosis of the disease. By studying the sense of smell and its link to early-stage PD, we hope to better understand what causes neurons to be lost, and perhaps how to slow their death. The promising results of this study warrant further investigation," concluded Ms. Peters.

Founded in 1931 as the Harvey Cushing Society, the American Association of Neurological Surgeons (AANS) is a scientific and educational association with more than 7,400 members worldwide. The AANS is dedicated to advancing the specialty of neurological surgery in order to provide the highest quality of neurosurgical care to the public. All active members of the AANS are certified by the American Board of Neurological Surgery, the Royal College of Physicians and Surgeons (Neurosurgery) of Canada or the Mexican Council of Neurological Surgery, AC. Neurological surgery is the medical specialty concerned with the prevention, diagnosis, treatment and rehabilitation of disorders that affect the entire nervous system, including the spinal column, spinal cord, brain and peripheral nerves.

The author reports no conflicts of interest.

Media Representatives: If you would like to cover the meeting or interview a neurosurgeon " either on-site or via telephone " please contact the AANS Communications Department at (847) 378-0517 or call the Annual Meeting Press Room beginning Monday, May 4 at (619) 525-6252.