Ataxia and tolerance after thalamic deep brain stimulation for essential tremor.

BACKGROUND: Deep brain stimulation (DBS) of the ventral intermediate nucleus (VIM) thalamus is highly effective to treat medication-refractory essential tremor (ET). Complications of stimulation-induced ataxia and tolerance have been reported in limited series, ranging from 5 to 40%. OBJECTIVE: We analyzed a large single-center cohort of ET patients treated with thalamic DBS to assess rates of ataxia and tolerance. METHODS: Retrospective study of all ET patients that underwent VIM DBS at Mayo Clinic from 2010 to 2014. Demographic, clinical and DBS data were extracted. Risk factors, complications and time to onset of tolerance and ataxia were examined. RESULTS: One hundred and thirteen ET patients (51% male) of mean age 68 ± 10 years and mean ET duration 27 ± 18 years underwent DBS during the study period. Of these, 98 (87%) had follow-up of ≥6 months (mean 4.0 ± 1.5 years) and were included for analysis. Complications of isolated ataxia (26%), isolated tolerance (4%), both tolerance and ataxia (9%), or neither (61%) were identified. Development of ataxia was about 3 times more common than tolerance (35% vs. 13%). The mean time to ataxia was 5.5 ± 0.3 years postoperatively. Risk factors for ataxia were baseline ataxic features, older age, and shorter ET disease duration. Small sample size limited calculation of risk factors and onset time for tolerance. CONCLUSIONS: Stimulation-related ataxia occurred in one-third of ET patients, while tolerance was less common. Presence of baseline ataxia, age, and disease duration may aid counseling of stimulation-related ataxia risk. Larger studies are warranted to confirm these findings and further assess risk factors for tolerance.

STN Versus GPi Deep Brain Stimulation for Action and Rest Tremor in Parkinson's Disease.

OBJECTIVE: To investigate the effects of subthalamic nucleus (STN) and globus pallidus internus (GPi), deep brain stimulation (DBS) on individual action tremor/postural tremor (AT) and rest tremor (RT) in Parkinson's disease (PD). Randomized DBS studies have reported marked benefit in tremor with both GPi and STN and DBS, however, there is a paucity of information available on AT vs RT when separated by the surgical target. METHODS: We retrospectively reviewed the 1-year clinical outcome of PD patients treated with STN and GPi DBS at the University of Florida. We specifically selected patients with moderate to severe AT. Eighty-eight patients (57 STN and 31 GPi) were evaluated at 6 and 12 months for changes in AT and RT in the OFF-medication/ON stimulation state. A comparison of "response" was performed and defined as greater than or equal to a 2-point decrease in tremor score. RESULTS: STN and GPi DBS both improved AT at 6- and 12-months post-implantation (p < 0.001 and p < 0.001). The STN DBS group experienced a greater improvement in AT at 6 months compared to the GPi group (p = 0.005) but not at the 12 months follow-up (p = 0.301). Both STN and GPi DBS also improved RT at 6- and 12-months post-implantation (p < 0.001 and p < 0.001). There was no difference in RT scores between the two groups at 6 months (p = 0.23) or 12 months (p = 0.74). The STN group had a larger proportion of patients who achieved a "response" in AT at 6 months (p < 0.01), however, this finding was not present at 12 months (p = 0.23). A sub-analysis revealed that in RT, the STN group had a larger percentage of "responders" when followed through 12 months (p < 0.01). CONCLUSION: Both STN and GPi DBS reduced PD associated AT and RT at 12 months follow-up. There was no advantage of either brain target in the management of RT or AT. One nuance of the study was that STN DBS was more effective in suppressing AT in the early postoperative period, however, this effect diminished over time. Clinicians should be aware that it may take longer to achieve a similar tremor outcome when utilizing the GPi target.

Parkinson's disease: Diagnosis and appreciation of comorbidities.

Parkinson's disease (PD) is a complex neuropsychiatric disorder that manifests with a variety of motor and nonmotor symptoms. Its incidence increases with age. It is important for clinicians to be able to distinguish symptoms of aging and other comorbidities from those of PD. The diagnosis of PD has traditionally been rendered using strict criteria that mainly rely on the cardinal motor symptoms of rest tremor, rigidity, and bradykinesia. However, newer diagnostic criteria proposed by the Movement Disorders Society for diagnosis of PD collectively reflect a greater appreciation for the nonmotor symptoms. The treatment of PD remains symptomatic and the most noticeable improvements have been documented in the motor symptoms. Levodopa remains the gold standard for therapy, however there are now many other potential medical and surgical treatment strategies. Nonmotor symptoms have been shown to affect quality of life more than the motor symptoms. There is ongoing research into symptomatic and disease modifying treatments. Given the multisystem involvement in PD, an interdisciplinary patient-centered approach is recommended by most experts. This chapter addresses first the diagnostic approach and the many geriatric considerations. This is followed by a review of the nonmotor symptoms. Finally, a summary of current treatment strategies in PD is presented along with potential treatment complications.