Locomotor response to levodopa in fluctuating Parkinson's disease

The aim of this study was to quantify the dynamic response of locomotion to the first oral levodopa administration of the day in patients with fluctuating Parkinson's disease (PD). Stride length, walking speed, cadence and gait variability were measured with an ambulatory gait monitor in 13 PD patients (8 males) with a clinical history of motor fluctuations. The Unified Parkinson's Disease Rating Scale (UPDRS) gait score (part 29) was also determined by a movement disorders specialist from video recordings. Subjects arrived in the morning in an 'off' state (no PD medication) and walked for a maximum length of 100 m. They then took their usual morning dose of oral levodopa and repeated the walking task at 13 min intervals (on average) over a 90 min period. Changes in stride length over time were fit with a Hill (Emax) function. Latency (time until stride length increased 15% of the difference between baseline and maximum response) and the Hill coefficient (shape of the 'off-on' transition) were determined from the fitted curve. Latency varied from 4.7 to 53.3 min post-administration [23.31 min (SD 14.9)], and was inversely correlated with age at onset of PD (R = -0.83; P = 0.0004). The Hill coefficient (H) ranged from a smooth hyperbolic curve (0.9) to an abrupt 'off-on' transition (16.9), with a mean of 8.1 (SD 4.9). H correlated with disease duration (R = 0.67; P = 0.01) and latency (R = 0.67; P = 0.01), and increased with Hoehn & Yahr stage in the 'off' state (P = 0.02) from 5.7 (SD 3.5) (H&Y III) to 11.9 (SD 4.7) (H&Y IV). Walking speed correlated with changes in mean stride length, whereas cadence and gait variability did not. UPDRS gait score also reflected improving gait in the majority of subjects (8), providing clinical confirmation of the objective measures of the locomotor response to levodopa. Increasing abruptness (H) of the 'off-on' transition with disease duration is consistent with results from finger-tapping studies, and may reflect reduced buffering capacity of pre-synaptic nigrostriatal dopaminergic neurons. Ambulatory monitoring of gait objectively measures the dynamic locomotor response to levodopa, and this information could be used to improve daily management of motor fluctuations.