Freezing in-on and parkinson's disease: Cognition and behavior

Freezing of gait (FOG) refers to transient episodes, usually lasting seconds, in which a patient is unable to initiate or continue locomotion, occurring on a background of relatively good ability to move and is best described by patients as "feet get glued to the ground." Freezing of gait is common in Parkinson's disease, with increasing prevalence as the disease progresses, but it has been commonly reported in pathologically proven progressive supranuclear palsy and vascular parkinsonism. Two types of freezing of gait have been recognized in patients affected by Parkinson's Disease, taking L-Dopa. The most common is an "off" -freezing of gait, which can be improved with L-Dopa or dopaminergic treatment, such as apomorphine. "Off" -freezing appears during an "off" state, when the patient is generally bradykinetic and rigid. In contrast, "on" -freezing is characterized by a worsening of symptoms as the dose of L-Dopa is increased, and by a general improvement, as the dose is decreased or, better said, modulated. The onfreezing of gait is related to abnormal execution of complex motor tasks such as repetitive, simultaneous, or sequential motor acts. Different Authors suggested that the primary underlying abnormality might be related to the inability to deliver, or hold a pre-programmed, continuous, and complex motor act, in response to an established and correct internal plan of action. Therefore, we hypothesized that PD- on freezing patients might be clinically well differentiated from the other clinical subtypes of PD and might present a specific cognitive impairment, different from that presented by PD patients, without on-FOG. We discuss these hypothesis, based on clinical studies and follow-up.