Patterns of failure of deep brain stimulation

The importance of Deep Brain stimulation (DBS) for the treatment of movement disorders is still growing. Many reports have been published so far on safety and effectiveness of DBS. For Parkinson symptoms STN has been determined as the target of choice, for tremor dominant disorders the VIM and the Gpi for dystonia. In order to evaluate predictors for the outcome of DBS we retrospectively reviewed and analyzed the cases of failure of DBS surgery.

Between 1996 and 2004 303 deep brain electrodes were implanted in 166 patients in two centres. Parkinson's disease (PD) was found in 94 patients, of which the first 8 PD patients underwent GPi surgery. Since STN was found to be the more effective target for DBS, we used this target for PD patients, regardless of the predominant symptom. Among 57 tremor patients, 4 suffered from posttraumatic tremor, 13 from tremor related to multiple sclerosis, different types of essential tremor was the indication for surgery in another 40 patients. VIM was the target for tremordominant disorders, 15 patients with Dystonia were treated with GPi electrodes.

For the evaluation of PD patients UPDRS III motor score was performed. Tremor patients were evaluated according to the Essential Tremor Rating scale. Severity of dystonia was measured using BFMDRS. Activity of daily living score was determined in all patients.

We considered the operation as successful, if both a significant improvement in the Activity of Daily living was reported by the patients and if no permanent morbidity was determined at the 6 months follow-up.

There was a significant improvement (p<0,001) in motor function (UPDRS III) for PD patients stimulated in the STN (preop. med on/off: 31/51, 6 m postop. stim on -med on/ stim off -med off: 19/51). Tremor patients also significantly benefited from surgery (ETRS preop/6 months postop.: 65.6/26.6). In dystonia patients different results were achieved: While DYT-1-positive patients markedly improved, the success in secondary dystonia was only limited. The overall surgery related complication rates were 18% for the STN (16/86 patients), 7% for the VIM (4/57) and 17% for the GPi (4/23). Several reasons for failure of surgery were determined: in 2 patients retrospectively Multi System Atrophy was considered, in 2 patients effective stimulation in the STN lead to manic behaviour, 5 patients developed progressive dementia in the follow-up course. Psychotic deteriorations commonly occurred in cases of bilateral DBS in the STN (26 out of 86 patients). However, these were transient in most of the patients. In 5 patients permanent deficits lead to a reduction of DBS success. In 6 patients suboptimal electrode position limited the benefit from stimulation.

In conclusion it became obvious that careful selection of patients, accurate target determination, state of the art imaging techniques) and sophisticated neuropsychological screening are required to avoid DBS failure.