Freezing of gait in early Parkinson's disease: Nigral iron content estimated from magnetic resonance imaging.

ABSTRACT

PURPOSE: Freezing of gait is a major source of disability associated with the progression of Parkinson's disease (PD). Our objective was to determine whether evolving changes in nigral iron content in association with declining motor function in early PD differentiates subjects who develop freezing from those who do not. METHODS: A cohort of previously untreated individuals with early PD (n=19) was followed for 36 months clinically and with MRI. The cohort was divided into two groups based on the development of freezing during follow-up. A multiple gradient echo MRI sequence provided an index of basal ganglia iron content. RESULTS: There were significant baseline differences between those who developed freezing (n=7) and those who did not (n=12) in Unified Parkinson's Disease Rating Scale motor scores, time to complete a 14 m walk and timed up and go. There was a significant correlation between the measured change in transverse relaxation in the lateral substantia nigra pars compacta and the change in motor score from baseline to 36 months (p=0.002). The freezing group showed a greater change in motor score and iron content than did the non-freezing group. CONCLUSIONS: Individuals destined to develop freezing early in PD have more motor impairment at baseline, more rapid deterioration in motor function, and pars compacta changes suggestive of increased iron content in comparison to those who do not.