The effects of levodopa on tongue strength and endurance in patients with Parkinson's disease.

The aim of this study is to investigate the effects of levodopa on measures of strength and endurance of tongue muscle contraction in patients with Parkinson's disease (PD). Ten patients with idiopathic PD were included. All patients were studied in practically defined on- and off-phases. They were asked to perform isometric tongue protrusions, which were registered by means of a calibrated tocograph. Results of on- and off-conditions were compared using non-parametric tests. Maximum force and contraction duration did not differ significantly between both conditions, but the integrated measurement of both (area under curve) was significantly larger in the on-state. The force decay slope was significantly lower in the on-state. No correlations were found with disease severity, disease stage or age. These findings fit the known pathophysiological effects on patterns of isometric muscle contraction in PD. It remains to be demonstrated if the effects of levodopa on tongue strength and endurance correlate with alterations in speech intelligibility, articulation and respiration.