Myometry revealed medication-induced decrease in resting skeletal muscle stiffness in Parkinson's disease patients.

BACKGROUND: Based on combined analysis of clinical assessment of parkinsonian rigidity (constant resistance force generated during passive movement in a joint), electromyography and/or dynamometry many studies showed objectively that anti-parkinsonian medication decreases the rigidity in Parkinson's disease (PD). Rigidity-related changes in resting muscle stiffness (changed muscle's mechanical property related to its structural changes and changed neural drive) in PD patients have been revealed by myometry, a simple, sensitive, and reliable method for measuring mechanical properties in human soft tissues. However, an application of myometry in estimation of medication effects on the PD rigidity-related muscle stiffness has not been reported yet. Therefore, our study aimed to assess medication-induced changes in resting muscle stiffness in PD patients using myometry.

METHODS: We measured resting muscle stiffness by myometry and recorded a surface electromyogram of relaxed biceps brachii, brachioradialis and triceps brachii muscles in ten patients with PD (age: 51-80 years; Hoehn and Yahr stage: 2.5-4) during medication on-phase (when subjects felt best comfort and fitness after medication: Levodopa, Piribedil, Ropinirol) and medication off-phase (12h after withdrawal of the medication).

FINDINGS: Our patients had significantly lower myometric stiffness and electromyogram amplitude in all tested muscles, and also lower clinical rigidity scores during the medication on-phase compared with the medication off-phase.

INTERPRETATION: Myometry revealed that anti-parkinsonian medication decreases not only rigidity in PD, but also rigidity-related stiffness in resting skeletal muscles in PD patients. These findings show that myometry can enrich neurological practice, by allowing objective and reliable assessment of parkinsonian rigidity treatment effectiveness.