The present results suggest that prior to surgery patients with Parkinson's disease can be assigned to four distinct psychosocial profiles. Even three years after STN DBS this patient classification remained unchanged. Up to one year postoperatively there was transient improvement in mood which had no influence on group membership. The improvement disappeared in the three-year follow-up as scores returned back to baseline level. In conclusion, STN DBS only transiently improved mood and psychosocial functioning at one year. In the three-year follow-up this positive effect disappeared and returned to baseline. Thus, in the long run there was no deterioration in mood and psychosocial functioning compared to the preoperative state.
A cluster analysis revealed different psychosocial profiles that varied in well-being, depressive and anxious symptoms, distress and sickness impact. Two clusters were characterized by low well-being and moderate to high sickness impact. By comparison, the other groups were less impaired in psychosocial functioning.
Three, six and twelve months after surgery all patients improved their psychosocial characteristics but patients of cluster one and two still showed disadvantageous profiles. Three years postoperatively these ameliorations were absent but the profiles of all clusters remained relatively unchanged compared to baseline level.
Based on the patient classification of the cluster analysis it may possible to individually adjust psychosocial support to patients' needs. We assume that patients appending to cluster one or two might need more psychological support, patients of cluster three and four need less. The required amount of psychological support could be determined even prior to surgery as the psychosocial profiles remained unchanged in the course of time.
Up to one year after surgery comparisons of group means before and after surgery showed marked improvements in the majority of psychosocial variables. Well-being significantly increased, depressive and anxious symptoms, sickness impact as well as the distress level declined. These results are consistent with the findings of other groups [8
]. Scores of three subscales (depression, fatigue and vigor) of the POMS were diminished at three, six and twelve months but these results only showed a trend towards significance. At the three-year follow-up they returned to baseline level. The bottom line is no impairment in mood and psychosocial functioning evolved in the long-term follow-up. Concordantly, no significant changes in depressive or anxiety symptoms have been reported in other studies [35
]. Previous studies even reported worsening of depressive symptoms in a subgroup of patients [11
]. In a recent review the overall finding was that in larger subgroups STN DBS rather had an antidepressant than depressant effect [37
So far there are only few long-term studies with respect to mood alterations after STN DBS. One study revealed a reduction of depressive symptoms but increased apathy and thought disorders in the three-year follow-up [8
]. In agreement with our results other authors found less (although not significantly) depressive symptoms one year after surgery [5
]. Three and even five years after electrode implantation there was no difference to baseline level.
In line with previous studies the improvement of motor function declined to small extent but remained stable during the entire observation period [5
In a previous study depressive symptoms were significantly improved three months after surgery, but the extent of depressive symptoms increased at twelve months and did not differ from baseline level [7
]. Compared to baseline another group found no changes after STN DBS in depressive symptoms (six, 24 months and five years postoperatively) [38
]. Accordingly in our study beneficial effects on well-being, depressive symptoms, state and trait anxiety, as well as on sickness impact found up to one year after STN DBS disappeared three years postoperatively.
These results suggest that motor outcome is not related to psychosocial functioning. One might ask why mood and well-being of patients declined to the initial point even though motor symptoms remained improved three years after surgery. One possible explanation of that effect stems from economic psychology. According to the prospect theory values and preferences are not entirely stable [39
]. A recently gained profit or advantage soon becomes a matter of course. Based on that new status quo, losses are experienced more powerful even though they are smaller than the antecedent gains. This might be equally valid for the current results. Although ADL and motor function slightly declined in the long-term follow-up there still was a significant improvement compared to baseline. The bottom line was a net profit which may not have been perceived by patients as they only recognized the proportionally small loss. However, in conclusion STN DBS had beneficial effects on motor function and activities of daily living up to three years after surgery.
In summary, STN DBS did not induce deterioration of mood and psychosocial functions in our patients. The results showed beneficial short-term effects on mood and psychosocial functions after one year. In the three-year follow-up these beneficial effects were absent and scores returned to the preoperative level. Only amelioration of somatic symptoms and anxiety measured by the Symptom-Checklist-90-R persisted up to three years which may be related to the overall decline of motor symptoms. In this regard it is of note that a previous study reported of a gain of quality of life in parkinsonian patients twelve months after electrode implantation which however was restricted to physical aspects [40
]. Mental and social quality of life did not change in the course of time. Although they used PD specific scales their findings are in line with the current results.
Based on our data we found that patients can be assigned to distinct psychosocial profiles prior to surgery. Since patient classification did not change in the course of time the individual amount of psychosocial support can eventually be anticipated before surgery in order to prevent or early detect behavioural abnormalities after STN DBS. In this regard, further studies should determine how personality traits influence subjective well-being.
Before surgery patients of cluster 1 displayed clinical relevant depression and patients of cluster 2 and 3 were moderately depressed. Their depressive pathology ameliorated up to one year and long-term results revealed at least no worsening.
Inclusion criteria of the CAPSIT-PD panel recommend surgery only for patients free of behavioural abnormalities because mainly in single case studies deterioration has been observed after surgery [26
]. Besides, behavioural abnormalities mostly appeared to be transient and results are too heterogeneous to define universally valid selection criteria. Following the current inclusion criteria patients with diagnosed depression are usually meant to be excluded from STN DBS.
Despite some methodological limitations, especially the small number of patients, our findings show that STN DBS is an effective treatment PD patients with mild psychosocial disturbances. Based on the results of the cluster analysis it is possible to classify patients according to their psychosocial profile even before surgery. This allows individual determination of the extent of the collateral psychological support that is required before surgery and even in the long run.