Mental Side Effects of Deep Brain Stimulation (DBS) for Movement Disorders: The Futility of Denial

Abstract

The benefits of deep brain stimulation for parkinsonian patients are well documented and have established the method as mainstay in the late stages of the disease (Deuschl et al., 2006). However, early in the history of the method reports of mental side effects were published. In 1995 Limousin and colleagues reported transient confusion and hallucinations with one of their first patients (Limousin et al., 1995). Further reports with disturbing side effects accumulated over time (Krack et al., 2001; Berney et al., 2002; Herzog et al., 2003a). While cognitive squeals were studied in numerous papers (Funkiewiez et al., 2004; Contarino et al., 2007) but are generally conceived to have little impact on the quality of life (Schupbach et al., 2006), the field of psychiatric effects was more hesitantly explored. Results to the latter remain ambiguous with a tendency toward less severe side effects in the large series of experienced centers (Deuschl et al., 2006; Weaver et al., 2009). Adverse events in this domain were largely attributed to acute effects weaning over a short period (Herzog et al., 2003b). However, over the years I have seen a considerable number of patients both operated by myself but also from other experienced centers who showed psychological symptoms that counteracted the improvements in motor function. This personal experience is in line with patients and their representatives who voice concern over these phenomena with their deleterious impact on the wellbeing of patients, their families and caregivers (personal communication, F-W. Mehrhoff, Geschaftsfuhrer, Deutsche Parkinsonvereinigung, Nov. 2014). Such concerns also appear quite regularly in patient support group meetings. My impression is, that patients and their representatives feel their concerns not appropriately reflected in the scientific literature and expert opinions. This comment responds to such observations with the aim to reposition the defense of DBS for Parkinson's disease. Reluctance to delve into this subject may in my opinion eventually leave those who offer the procedure defenseless toward reproach from patients, referring colleagues and the general public. One may counter such observations by outlining that, particularly in case of complex psychiatric side effects, there are no objective means of deciding when a treatment has to be considered a failure or a success. Patients and relatives have also the propensity to underestimate their preoperative disabilities (Herzog et al., 2003b). This is further complicated by the fact that PD is a disease with cognitive, affective, and behavioral symptoms and thus has a neuropsychiatric impact on the patient as well. DBS may even in some cases restore the original personality, which then is simply not fitting any more into the actual social and familial setting. Finally, also medication-based therapies for PD can have severe neuropsychiatric effects (Cools et al., 2003). Nevertheless, there remains a substantial proportion of DBS patients with severe and lasting behavior disturbances, which were credibly not present in the ultimate preoperative phase and that also has led to critical comments in the literature (Moro, 2009). These comprise reckless driving or other forms of risk-seeking behavior and even aggressive and contemptuous behavior toward relatives and spouses. In some cases this can be remedied by moving the active contacts outside the STN with subsidence of aggressive behavior within hours. This hints to a direct effect of stimulation. Unfortunately in some patients stimulation must be markedly reduced or switched off completely to ameliorate psychiatric effects. Numerous reports and case series have contributed to this issue with delineation of alarming psychiatric disturbances ranging from hypomania to suicidal ideation and suicide (Herzog et al., 2003a; Morgan et al., 2006; Schupbach et al., 2006; Witt et al., 2008). At the same time other publications failed to find relevant changes of personality and behavior (Schuepbach et al., 2013), considered significant changes as not relevant for overall quality of life (Morgan et al., 2006) or even found much higher incidence of psychoses in the control group compared to the DBS group. I will now elaborate on these issues in some more detail.