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That high frequency stimulation of the thalamus suppresses tremor associated with Parkinson's disease (PD) has been recognised since the early attempts to treat movement disorders by ablative procedures in the 1960s. 1, 2 Deep brain stimulation (DBS), however, was not utilised as a viable alternative to ablative therapies until the early 1990s. 3 This procedure is now the preferred surgical approach in patients with PD who experience troublesome levodopa related motor complications, and in patients with severe essential tremor (ET) and other medically intractable, disabling disorders, such as dystonia, cerebellar outflow tremor, and hemiballism. When these movement disorders cannot be adequately controlled with available treatments, they may have profoundly detrimental effects on patients' health related quality of life (HRQoL), defined by the World Health Organization as "perception of their position in life in the context of the culture and value systems in which they live and in relation to their goals, expectations, standards and concerns". 4 Instruments that measure HRQoL allow clinicians to understand the burden of the disease and serve as useful tools for assessing the impact of therapeutic interventions on activities of daily living (ADL), employment, and other functions. 5 There are two types of HRQoL instruments, generic and disease specific. Generic instruments are multidimensional questionnaires that cover a wide variety of areas and can be applied to many diseases. Although these allow comparisons between diseases, 5 they lack sensitivity in areas important to patients with movement disorders. Disease specific HRQoL questionnaires are tailored to what a particular patient population feels is important; therefore, they allow more accurate information regarding the impact of a disease on the overall health burden. 5 The primary objective of this paper is to systematically and critically review the available literature on the effects of DBS on HRQoL in ET, PD, dystonia, and cerebellar outflow tremor related to multiple sclerosis (MS). For in-depth discussion on the individual HRQoL instruments discussed in this article, we direct the readers to other reviews. 6, 7
METHODS
We reviewed the literature in English from 1965 to 2005 using the following sources to identify clinical studies: Medline, Pre-medline, Sociofile, Psych Info, Health and Psychosocial instruments, Healthstar, the Cochrane Library, and reference lists of included publications. We used the following search terms: Parkinson's disease,...