Lateralisation of Parkinson symptoms and visuomotor control in gait

The aim of this retrospective study was to assess the presence of a possible association between handedness and the side of symptom dominance in 963 patients with Parkinson’s disease. In only 287 patients the hand dominance was registered. Out of 254 right-handed patients, 158 (62%) had a right-side dominance of Parkinson symptoms, while 96 patients (38%) had left-lateralised symptom dominance (p < 0.001). For the 33 left-handed subjects, 18 (55%) had leftand 15 (45%) had right-sided symptom dominance (p = 0.602). Righthandedness thus appeared to be associated with right-sided dominance of Parkinson symptoms, while the group of left-handed patients was too small to draw conclusions from. Possible explanations are discussed. 2 Handedness and dominant side of symptoms in Parkinson's disease | 27 INTRODUCTION Parkinson’s disease is characterised by asymmetry of symptoms at the onset of disease which is generally maintained during disease progression. Assessment with positron emission tomography (PET) has demonstrated a consistent relation between symptom asymmetry and lateralised cerebral function, in such a way that the dominant side of symptoms significantly correlated with reduced dopamine transporter uptake in the contralateral hemisphere. The cause of symptom lateralisation in Parkinson's disease, however, remains to be elucidated (Djaldetti et al., 2006). A well-known lateralised function in normal conditions is hand dominance, which is related to asymmetry across brain systems (Liu et al., 2009). One might speculate whether such brain asymmetry could provide a clue for a possible explanation for lateralisation of Parkinson symptoms. In that case a relation between handedness and such symptom lateralisation might be expected. This issue has been addressed in a few previous studies, with varying results. Although these studies generally concerned small groups, a relation between hand dominance was suggested in some studies (Reynolds and Locke 1971; Uitti et al., 2005; Yust-Katz et al., 2008) but not in all (Klawans 1972; Štochl et al., 2009; van Rooden et al., 2009). The aim of the present retrospective study was to identify a possible association of handedness with the side of symptom dominance in Parkinson's disease. Moreover, we looked whether a relation could be found between gait associated disease characteristics and the side of symptom dominance. METHODS Study population Parkinson patients were retrospectively identified from a database of the Movement Disorders unit from the neurology department of the university medical centre Groningen. This database contained a total of 1120 patients with the diagnosis Parkinson's disease, seen over a period of about nine years. After assessment of the patient files, 157 patients were excluded for reasons such as uncertainty about the diagnosis Parkinson's disease, adjustment of the diagnosis, too many missing data or bilateral disease onset. A group of 963 subjects thus remained. Approval by the local ethical committee was not required for this study as it concerned retrospective analysis of patient files only. The dominant side of symptoms was based on documented clinical examination, which remained the same over time. Handedness was defined as the reported hand used for writing. To provide support for the correctness of the documented handedness, handedness was also assessed by phone in a small group of patients. In all these interviewed Parkinson patients, of which 26 were documented right-handed and 4 were documented left-handed, the documented