[Supra-on state freezing of gait: two case reports]

Over recent years, several types of freezing of gait (FOG) have been described, mainly according to their response to levodopa. FOG in Parkinson's disease presents in a variety of ways due to differences within the underlying pathophysiology. In a number of patients, increasing the dopaminergic stimulation may not improve this condition, and may even worsen it.

We present two patients with Parkinson's disease who were evaluated during off, on and supra-on periods. Motor function was assessed with Unified Parkinson's Disease Rating Scale III, tapping test on lower limbs and quantification of FOG episodes during each of these periods. Both patients presented FOG episodes while in off period, experiencing a significant improvement during on period. However, when increasing the dopaminergic stimulation in order to try to improve their motor response, FOG episodes worsened to the point of impairing gait.

FOG episodes are not always a consequence of akinesia or rigidity. Regarding the pathophysiology, the lack of an appropriate response to treatment would be explained by the involvement of structures exceeding the substantia nigra and the dopaminergic deficit. FOG worsening during periods of dopaminergic overstimulation could be related to a neurotransmitters disbalance affecting other nuclei involved in postural and gait control.