Cortical asymmetry in Parkinson's disease: early susceptibility of the left hemisphere. Issue 12 (6th October 2016) - Claassen, Daniel O.
Abstract: Background and Purpose: Clinically, Parkinson's disease (PD) presents with asymmetric motor symptoms. The left nigrostriatal system appears more susceptible to early degeneration than the right, and a left‐lateralized pattern of early neuropathological changes is also described in several neurodegenerative conditions, including Alzheimer's disease, frontotemporal dementia, and Huntington's disease. In this study, we evaluated hemispheric differences in estimated rates of atrophy in a large, well‐characterized cohort of PD patients. Methods: Our cohort included 205 PD patients who underwent clinical assessments and T1‐weighted brain MRI's. Patients were classified into Early ( n = 109) and Late stage ( n = 96) based on disease duration, defined as greater than or less than 10 years of motor symptoms. Cortical thickness was determined using FreeSurfer, and a bootstrapped linear regression model was used to estimate differences in rates of atrophy between Early and Late patients. Results: Our results show that patients classified as Early stage exhibit a greater estimated rate of cortical atrophy in left frontal regions, especially the left insula and olfactory sulcus. This pattern was replicated in left‐handed patients, and was not influenced by the degree of motor symptom asymmetry (i.e., left‐sided predominant motor symptoms). Patients classified as Late stage exhibited greater atrophy in the bilateral occipital, and right hemisphere‐predominant cortical areas. Conclusions: We show that cortical degeneration in PD differs between cerebral hemispheres, and findings suggest a pattern of early left, and late right hemisphere with posterior cortical atrophy. Further investigation is warranted to elucidate the underlying mechanisms of this asymmetry and pathologic implications. Abstract : In this study, we evaluated hemispheric differences in estimated rates of atrophy in a large, well‐characterized cohort of PD patients. We describe a pattern of early left‐lateralized cortical atrophy, which holds true regardless of handedness or side of motor severity. Our findings are consistent with previous reports of a left‐lateralized distribution of cortical atrophy in PD and other neurodegenerative disorders. Further investigation is warranted to elucidate the underlying mechanisms of this asymmetry and its implications for pathogenesis in neurodegeneration.