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Stereotactic surgical ablation of the thalamic nucleus (thalamotomy) has long been applied to parkinsonian tremor, rigidity, and levodopa induced dyskinesias.1–3 Chronic high frequency deep brain stimulation (DBS) of the thalamus, the globus pallidus internus (GPi), and the subthalamic nucleus (STN) has been widely used as an alternative to ablative surgery in the treatment of Parkinson’s disease (PD). STN stimulation has become increasingly popular because it can result in a striking improvement of motor symptoms and the ability for PD patients to pursue the activities of daily living.45 We report that STN stimulation markedly alleviated axial motor symptoms in a PD patient who had undergone bilateral thalamotomy more than 20 years earlier.
This 70 year old right handed woman presented for the first time to our university hospital in early 2002. Around 1968, she developed right sided tremor and bradykinesia and was diagnosed with PD. Although she initially responded well to medication, her symptoms progressed, with worsening motor fluctuations including dyskinesia. Left and right thalamotomy, performed in 1976 and 1982 respectively, resulted in marked improvement of her tremor and dyskinesia. She received optimised medication and for the next 10 years was able to continue her job as a secretary. However, she developed slowly worsening postural instability with hesitant and shuffling gait, and suffered occasional falls.
Admission examination in March 2002 disclosed no neurological signs apart from parkinsonism. Under the administration of carbidopa/levodopa (4×5.0/50 mg/day), cabergoline (3×1.0 mg/day), amantadine hydrochloride (3×50 mg/day), and l-threo-DOPS (3×100 mg/day), neither rest tremor nor rigidity were apparent. Her bradykinesia was slight and more pronounced on the left side. Among her parkinsonian disabilities, axial symptoms including postural instability and gait disorder were the most pronounced. In the sitting position, her upper body was bent to the left. Without assistance she could not easily stand up, and her feet quickly froze when she attempted to walk forward. Shuffling hesitant steps were more marked on the left side and were particularly evident when turning, initiating gait, and walking backwards (fig 1A). They were not alleviated by visual aids such as stripes on the floor or by the use of an inverted walking cane. Her facial expression and speech were slightly affected and she manifested micrographia. On medication, her total and Part III motor scores on the Unified Parkinson’s Disease Rating Scale were 38 and 19, respectively. Magnetic resonance imaging (MRI) revealed no obvious abnormalities except for the surgical lesions produced 20 years earlier in the bilateral thalamic nuclei (fig 1B, C). Because she had experienced occasional transient drug induced psychoses that disappeared when the dosages were reduced, we concluded that it was not possible to improve her symptoms by pharmacotherapy alone and decided to perform stereotaxy. Prior informed consent was obtained from the patient and her family.
STN stimulation using two ventral contacts (contacts 0 and 1) gave rise to a striking improvement of her axial symptoms. Contacts 0 and 1 were used as cathode (fig 1D) and the pulse generator as anode. After extensive trials, the optimal stimulation parameters were determined to be 130 Hz frequency, 60 μsecond pulse width, and 1.8 V and 2.6 V amplitude at the first and final session, respectively. Under stimulation, she was able to stand up with ease and without assistance, and could initiate gait fluently. Her shuffling hesitant steps almost disappeared even when turning and walking backwards (fig 1E). Compared to preoperative baselines, her total and Part III motor scores were reduced from 38 and 19 to 11 and 5, respectively. She continued to take the same medication at the same doses as before and the beneficial effects of STN stimulation were unchanged at 9 months post-treatment.
Medically intractable PD has been addressed with different types of surgery. Our patient initially underwent staged bilateral thalamotomy. Although this procedure produced long lasting benefits and her tremor, rigidity, and dyskinesias were improved, bilateral, even staged, thalamotomy carries significant risks and is no longer considered a viable treatment option.2 Nonetheless, we recognised the long lasting effectiveness of bilateral thalamotomy; our patient was operated on 20 years earlier by Dr. Narabayashi.1 However, because of the recent aggravation of her axial parkinsonian symptoms, for which thalamotomy is generally thought to be ineffective,2 she was referred to our hospital for further treatment.
While STN DBS can markedly improve all levodopa responsive motor features of parkinsonism including axial symptoms,6 STN DBS appears to exhibit greater anti-parkinsonian effects than GPi DBS. Therefore, we chose STN stimulation for our patient. We initially thought that bilateral surgery was necessary. However, we found that unilateral (right) STN DBS contralateral to the more severely affected side markedly alleviated her axial symptoms, and led to the almost complete disappearance of her shuffling, hesitant steps and falling. At present, we do not know whether she will eventually require additional contralateral (left) STN DBS.
In patients with PD, various combinations of different stereotactic interventions have produced varying results and there is currently no consensus regarding their efficacy [for examples, see references 7 and 8]. Based on the experience reported here, we suggest that PD patients with a prior successful thalamotomy may be good candidates for STN stimulation.