 The relationship between WM lesions WM and Postural Instability Gait Disorders PIGD-PDin Parkinsons disease patients is largely unknown. We hypothesize that sub-clinical WM pathology may be a major contributing factor to PIGD-PD. We will compare two groups of patients with Parkinsons disease PD: those with PIGD and patients with dominant tremor n120to assess the role of brain WM changes. 