Measurement of rigidity in Parkinson's disease

Abstract

Clinical assessment of rigidity in parkinsonian patients is largely qualitative. The reliability and validity of the assessments are sometimes in doubt. Several "engineering" methods of quantifying rigidity have been described, but none has been adopted into general clinical practice. A possible reason is that these methods differ in crucial aspects from the clinical exam. We therefore tackled the problem by monitoring the clinical exam itself, using small sensors to measure the forces and displacements applied. Limb impedance (Z) was computed using parameter identification methods and compared to raters' verbalized ratings of rigidity based on a 5-point scale: the Unified Parkinson's Disease Rating System. The qualitative and quantitative estimates of impedance covaried over a fourfold range, depending on the forces imposed and the subject's motor set. Raters differed by up to 1 full point in their mean qualitative ratings and sometimes disagreed on whether levodopa reduced rigidity. This was not due to any significant differences in the overall range of rigidity they evoked, but rather to the way they scored this range [the ratio of mean rating to mean impedance (R/Z) varied between raters and subjects]. On the other hand, the R/Z ratio was reproducible over separate sets of ratings and may therefore serve to convert measured impedance into a standardized rating. Our results indicate that the current clinical exam may be too abbreviated to detect the sometimes quite small reductions in rigidity after levodopa. We conclude that a device that conveniently quantifies the clinical assessment of rigidity is now available and will lead to more standardized protocols for rating rigidity in the near future.

Unilateral subthalamic nucleus stimulation has a measurable ipsilateral effect on rigidity and bradykinesia in parkinson disease

“…However, these previous reports relied on clinical rigidity rating scales and did not employ objective, quantitative measures of rigidity. We measured rigidity using a validated analog scale (rigidity analyzer) that was demonstrated to be more sensitive and more reproducible than the rank-order scale widely used in clinical practice and studies (UPDRS) (Prochazka et al, 1997). In that validation study, under different testing conditions (such as on and off medication), mean UPDRS-rigidity ratings (R) of 4 experienced raters were plotted against the corresponding mean impedance measurements (Z) obtained using a rigidity analyzer in 7 PD patients with a wide range of rigidity severity.…”

“…The validity and reliability of the device and its use in measuring parkinsonian rigidity have been described (Patrick et al, 2001;Prochazka et al, 1997). Briefly, the device consists of an inflatable cuff force transducer and a gyro-based velocity sensor.…”

Muscle and joint elastic properties during elbow flexion in Duchenne muscular dystrophy

“…This should complete the clinical picture obtained by using devices where stiffness is only evaluated in terms of rigidity, i.e. resistance to motion performed by the examiner (Ghika et al 1993;Caligiuri, 1994;Prochazka et al 1997). However, further experiments combining mechanical and neurophysiological approaches are needed to improve knowledge of the predominant behaviour of passive and active structures that leads to the functional consequences observed in DMD.…”

Validation of portable muscle tone measurement device based on a motor-driven system

“…Another factor is the stretch velocity of imposed movement. In previous studies, the stretch movement was limited to relatively slow stretch velocity such that the acceleration/deceleration effects on the resistance were usually ignored [4]. However, higher stretching velocity is generally required, especially for observing velocity-dependent tests, such as the spasticity measurement.…”

“…In laboratory environment, m otor-driven systems which stretch the paretic limbs with various stretching modes for quantifying muscle tone have been developed [1][2] [3]. However, researchers have criticized the motor-driven systems are too cumbersome and inconvenient in clinical test environment [4]. Compared to motor-driven systems, hand-held systems seem to have advantages in providing an on-line quantification of muscle tone, especially in clinical routine examination or in surgical room.…”