On state freezing of gait in Parkinson disease A paradoxical levodopa-induced complication

Objective: To describe the phenotype of levodopa-induced on freezing of gait (FOG) in Parkinson disease (PD). Methods: We present a diagnostic approach to separate on FOG (deterioration during the on state) from other FOG forms. Four patients with PD with suspected on FOG were examined in the off state (>12 hours after last medication intake), on state (peak effect of usual medication), and supra-on state (after intake of at least twice the usual dose). Results: Patients showed clear on FOG, which worsened in a dose-dependent fashion from the on to the supra-on state. Two patients also demonstrated FOG during the off state, of lesser magnitude than during on. In addition, levodopa produced motor blocks in hand and feet movements, while other parkinsonian features improved. None of the patients had cognitive impairment or a predating off FOG. Conclusions: True on FOG exists as a rare phenotype in PD, unassociated with cognitive impairment or a predating off FOG. Distinguishing the different FOG subtypes requires a comprehensive motor assessment in at least 3 medication states. Neurology (R) 2012;78:454-457