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Quality of Life in DBS-STN: Introduction and Review

The Parkinson Alliance/DBS-STN Research Team

According to the World Health Organization: "Health is a state of complete physical, mental and social well-being, and not merely the absence of disease or infirmity" (WHO, 1952). This definition of health clearly conveys the importance of examining the concept of quality of life (QOL) and its role in medical illness. Although not easy to define, QOL generally refers to a patient's perception of the effects of an illness and its consequences on his or her life. Relevant components of QOL include "physical status and functional ability, psychological status, social interactions, economic and vocational status, and religious and spiritual issues" (Martinez-Martin, 1998). Thus, QOL concerns one's well-being above and beyond specific symptoms or disease severity. More and more, medical research is recognizing the need to assess QOL to more fully understand the effectiveness of various prevention, monitoring, and intervention techniques.(Devinsky, 1995).

A large amount of research has examined QOL in Parkinson's disease (PD). (Global Parkinson's Disease Steering Committee, 2002). This research has shown that many issues can influence a PD patient's subjective experience of QOL. Although an implicit assumption in the treatment of PD is that improvement in the cardinal symptoms of PD (rigidity, bradykinesia, tremor) will lead to an improvement in QOL, research has shown that QOL is not simply related to disease or symptom severity. (Schrag et al., 2000). Non-motor symptoms, psychiatric symptoms, social adjustment, vocational functioning, cognitive functioning, and other issues all play a role in QOL in PD. (Damiano et al., 1999).

Although many "generic" QOL measures have been used with PD patients, it is important to also use disease-specific tests of QOL (Patrick & Deyo, 1989). This is because symptoms of PD uniquely effect certain functions that are not relevant to all medical illnesses, such as communication (speech, handwriting, typing), eating (chewing, swallowing), and cognition (visual hallucinations, language, memory), among other issues. Although at least four PD specific QOL measures have been reviewed in detail (Marinus et al., 2002), the most commonly used measure is the Parkinson's disease questionnaire-39 (PDQ-39) (Peto et al., 1998). Very recently, another innovative QOL measure was developed specifically for PD patients undergoing deep brain stimulation (DBS) (Kuehler et al., 2003). A complete review of QOL in PD is beyond the scope of this article. What follows is a review of studies that have specifically examined QOL in patients who have undergone DBS of the subthalamic nucleus (STN). Our literature review identified 8 articles that formally measured QOL in DBS-STN patients. Of these, two (Gray et al., 2001; Mariz et al., 2003) studies included only a few patients with DBS-STN (6 and 3, respectively) among mixed samples of patients undergoing surgical treatment (e.g., thalamotomy, pallidotomy) or DBS of other brain regions (e.g., thalamus, pallidum).
 Unfortunately, these studies are limited because results were not reported specifically for the DBS-STN patients. A brief summary of a study reported in 2001 (Capus et al., 2001) found that in a sample of 7 patients with advanced PD, scores on the PDQ-39 improved by 50% at a six month follow-up evaluation. Unfortunately, this study only reported overall improvement and did not provide more detailed information about the specific dimensions of QOL assessed by the PDQ-39.

The largest study to date examined QOL in 60 patients with DBS-STN (Lagrange et al., 2002). Patients were administered the Parkinson's Disease Quality of Life scale (PDQL) (deMoer et al. 1996) before and 12 months after surgery. The results showed that the PDQL total score improved by 43%. In addition, emotional functioning improved by 29% and social functioning improved by 63%. Clearly, these results suggest that QOL improvements are seen in many patients following DBS-STN.

A study of 11 patients who underwent DBS-STN (Just & Ostergaard, 2002) found that, compared to a wait-list control group, significant improvements were evident across many, but not all, subscales of the PDQ-39 at three and six months post-surgery. Specifically, at six months post-surgery, the mobility, activity of daily living, and cognition subscales were significantly improved relative to controls. However, subscales measuring communication, bodily discomfort, social support, and emotional functioning were not significantly improved relative to the wait-list PD patients. This study stresses the importance of examining all of the dimensions of QOL in DBS-STN treatment research because some areas may improve while others do not.

In a study of 17 patients undergoing DBS-STN (Martinez-Martin et al. 2002), the PDQ-39 was administered before surgery and six months following surgery. This study found that the dimensions of mobility, activities of daily living, emotional functioning, stigma, and bodily discomfort all improved significantly. However, the areas of social support, communication, and cognition did not improve significantly. In a study of 20 DBS-STN patients (Daniele et al., 2003) using the PDQL, patients followed for 12 months showed an average improvement in QOL of 35%.

The most recent study of QOL in DBS-STN patients used the PDQ-39 in a sample of 26 patients who were followed for three months following surgery (Troster et al., 2003). This study showed an average improvement in PDQ-39 scores of 31%. Again, however, this study did not include information about specific subscale improvements and thus it is not possible to examine changes in specific functional domains. Importantly, this study did assess change in depressive symptoms and found that QOL improvement was significantly related to a reduction in symptoms of depression. In fact, these researchers found that improvement in QOL was more related to a decrease in depression than a decrease in motor symptoms. Overall, the studies reviewed reveal that QOL generally improves after DBS-STN. However, this is not true for all patients and the research conducted thus far on QOL in DBS-STN is limited in many ways (e.g., small sample sizes, lack of control groups, different tests assessing QOL). Future research will hopefully help us more fully understand what patient and treatment factors influence QOL outcomes in DBS-STN patients. We will continue to monitor this area of research and update this review upon the publication of further studies. Stay tuned!

References
Capus, L., Melatini, A., Zorzon, M., Torre, P., Carraro, N., Moretti, D., Gioulis, M., Morettie, R., Sarra, M.V., & Marsala, S.Z. (2001). Chronic bilateral electrical stimulation of the subthalamic nucleus for the treatment of advanced Parkinson's disease. Neurological Science, 22, 57-58. Damiano, A., Snyder, C., Strausser, B. & Willian, M. K. (1999). A review of health- related quality-of-life concepts and measures for Parkinson's disease. Quality of Life Research, 8, 253-243. Daniele, A., Albanese, A., Contarino, M.F., Zinzi, P., Barbier, A., Gasparini, F., Romito, L.M.A., Bentivoglio, A.R., & Scerrati, M. (2003). Cognitive and behavioural effects of chronic stimulation of the subthalamic nucleus in patients with Parkinson's disease. Journal of Neurology, Neurosurgery, and Psychiatry, 74, 175-182. deMoer, A.G.E.M, Wijker, W., Speelman, J.D., Hehaes, J.C.J.M. (1996). Quality of life in patients with Parkinson's disease: development of a questionnaire. Journal of Neurology, Neurosurgery, and Psychiatry, 61, 70-74. Devinsky, O. (1995). Outcome research in neurology: incorporating health-related quality of life. Annals of Neurology, 37, 141-142 Global Parkinson's Disease Survey Steering Committee (2002). Factors impacting on quality of life in Parkinson's disease: Results from an international survey. Movement Disorders, 17, 60-67. Gray, A., McNamra, I., Aziz, T., Gregory, R., Bain, P., Wilson, J., & Scott, R. (2001). Quality of life outcomes following surgical treatment of Parkinson's disease. Movement Disorders, 17, 68-75. Just H. & Ostergaard, K. (2002). Health-related quality of life in patients with advanced Parkinson's disease treated with deep brain stimulation of the subthalamic nuclei. Movement Disorders, 17, 539-545. Kuehler, A., Henrich, G., Schroeder, U., Conrad, B., Herschbach, P., & Ceballos- Baumann, A. (2003). A novel quality of life instrument for deep brain stimulation in movement disorders. Journal of Neurology, Neurosurgery, and Psychiatry, 74, 1023-1030. Lagrange, E., Krack, P., Moro, E., Ardouin, C., Van Blercom, N., Chabardes, S., Benabid, A.L., & Pollack, P. (2002). Bilateral subthalamic nucleus stimulation improves health-related quality of life in PD. Neurology, 59, 1976-1978. Marinus, J., Ramaker, C., van Hilten, J.J., & Stiggelbout, A.M. (2002). Health related quality of life in Parkinson's disease: a systematic review of disease specific instruments. Journal of Neurology, Neurosurgery, and Psychiatry, 72, 241-248. Mariz, G.M, Lindberg, M., Hariz, H.I., & Bergenheim, A.T. (2003). Gender differences in disability and health-related quality of life in patients with Parkinson's disease treated with stereotactic surgery. Acta Neurologica Scandinavia, 108, 28-37. Martinez-Martin, Pablo (1998). An introduction to the concept of "quality of life in Parkinson's disease." Journal of Neurology, 245, S2-S6. Martinez-Martin, P., Valldeoriola, F., Tolosa, E., Pilleri, M., Molinuevo, J.L., Rumia, J., & Ferrer, E. (2002). Bilateral subthalamic nucleus stimulation and quality of life in advanced Parkinson's disease. Movement Disorders, 17, 372-377. Patrick, D.L., & Deyo, R.A. (1989). Generic and disease-specific measures in assessing health status and quality of life. Medical Care, 27, S217-S232. Peto, V., Jenkinson, C., & Fitzpatrick, R. (1998). PDQ-39: a review of the development and application of a Parkinson's disease quality of life questionnaire and its associated measures. Journal of Neurology, 245, S10-S14. Schrag, A., Jahanshahi, M., & Quinn, N. (2000). What contributes to quality of life in patients with Parkinson's disease. Journal of Neurology, Neurosurgery, & Psychiatry, 69, 308-312. Troster, A., Fields, J., Wilkinson, S., Pahwa, R., Koller, W., & Lyons, K. (2003). Effect of motor improvement on quality of life following subthalamic stimulation is mediated by changes in depressive symptomatology. Stereotact. Funct. Neursurg., 80, 43-47. World Health Organization (1952). Handbook of basic documents, 5th Edition. Palais des Nations, Geneva, pp3-20.



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