Relationship between freezing of gait (FOG) and other features of Parkinson's: FOG is not correlated with bradykinesia.

Background: The pathophysiology of freezing of gait (FOG) is unclear.
Objective: To assess the relationships between FOG and other parkinsonian features in Parkinson's disease (PD), focusing on levodopa effects.
Methods: Nineteen PD patients with significant FOG in "off" were assessed while "off" and "on". Three observers independently viewed videotapes of a 130-m walk and scored FOG frequency. The Unified Parkinson's disease Rating Scale was used to evaluate clinical state.
Results: FOG frequency was not correlated with other parkinsonian features in "off" and only with speech and writing in "on". Levodopa significantly decreased FOG frequency (p<0.001). This reduction was strongly correlated with improvement of tremor (R=0.80, p<0.01) and speech (R=0.62, p<0.05), but not with improvement in rigidity, bradykinesia, or balance.
Conclusion: Levodopa decreases FOG in PD. FOG is apparently an independent motor symptom, caused by a paroxysmal pathology that is different from that responsible for bradykinesia, rigidity or postural instability.