Diagnostic value of the rapid assessment of postural instability in Parkinson's disease (RAPID) questionnaire

BACKGROUND

People with idiopathic Parkinson's disease (PD) develop postural instability in the later stages of the ailment. Postural instability has traditionally been quantified with the Pull test even though its face validity is limited. We previously established cut-off scores for a three-part rapid assessment of postural instability (RAPID) questionnaire as a non-physical complement to the physical test. In the current study, the questionnaire was administered to a new group of PD subjects to evaluate the diagnostic value of the instrument.

METHODS

Sensitivity and specificity values were calculated for single and combined sections of the questionnaire by using the Pull test as the gold standard for assessing the presence of postural instability.

RESULTS

The questionnaire when used in its entirety gave the highest sensitivity (.71), whereas specificity was highest in the activities of daily living (.74) and fear of falling sections (.74). Net specificity decreased to .44 when the scores from the three sections of the questionnaire were combined.

CONCLUSIONS

The high sensitivity of the RAPID questionnaire suggests that it may be used as an adjunct to the Pull test or solely if it is not convenient or contraindicated. The questionnaire may also be adapted for use via the telephone or internet. The limitation of the Pull test in revealing postural instability may explain the low specificity of the questionnaire, i.e. the questionnaire correctly identifies patients as unstable when the Pull test indicates normal postural control. It is hoped that the rapid identification of postural instability in PD may lead to increased awareness of the disease progression and fewer falls.

Rapid assessment of postural instability in Parkinson's disease (RAPID): a pilot study

BACKGROUND

The Fahn's pull (or retropulsion) test is an item in the motor section of the Unified Parkinson's Disease Rating Scale, which is used almost exclusively to classify postural instability in Parkinson's disease (PD). However, the test is hard to standardize and is often performed incorrectly, making it hard to interpret. Moreover, it may not be safe to administer in patients who experience pain in the shoulders, neck, trunk and/or lower extremities. Identifying and grading postural instability in PD without requiring a physical challenge would not only be useful for the clinician but would assist patients and caregivers in its recognition. We propose the use of the rapid assessment of postural instability in Parkinson's disease (RAPID) questionnaire as a non-physical assessment tool.

METHODS

We determined the associations between the pull test and items on a risk-assessment questionnaire that consisted of three parts: activities of daily living, fear of falling, and frequency of falling.

RESULTS

Significant correlations were found between the pull test and the predictor variables, which ranged between 0.51 and 0.56 whilst the correlations amongst the predictor variables ranged between 0.58 and 0.70. The three parts of the questionnaire, when used in combination, produced a 96% sensitivity in the classification of postural instability.

CONCLUSIONS

The RAPID questionnaire can be used as an adjunct to the pull test or solely if the pull test is contraindicated. It may also be possible to administer the questionnaire via the telephone or Internet. It is hoped that the rapid identification of postural instability would lead to fewer falls.

The strategies to regulate and to modulate the propulsive forces during gait initiation in lower limb amputees

We used the framework of motor program adaptability to examine how unilateral above-knee (AK) or below-knee (BK) amputee subjects organize the global and local biomechanical processes of generation of the propulsive forces during gait initiation to overcome the segmental and neuro-muscular asymmetry. The organization of the global biomechanical process refers to the kinematics behavior of the couple center of foot pressure (CoP) and center of mass (CoM); the organization of the local biomechanical process refers to the propulsive forces generated by the prosthetic or intact limb during the anticipatory postural adjustment phase and the step execution phase. Specifically, we examined: i) the strategy to regulate the progression velocity, i.e., to maintain it comparably when the leading limb changed from the prosthetic limb to the intact limb; and ii) the strategy to modulate the progression velocity, i.e., to increase it when gait was initiated with the prosthetic limb vs. intact limb. The kinematics of the CoM and CoP in the amputees showed the same global biomechanical organization that is typically observed in able-bodied subjects, i.e., the production of the forward disequilibrium torque was obtained by a backward shift of the CoP, followed by a forward acceleration of the CoM. However, gait initiation was achieved by using a different local strategy depending on which limb was used to initiate the step. For the regulation of the CoM progression velocity, when the gait was initiated with the intact limb, the slope of the progression velocity during the anticipatory postural adjustment phase (APA) was steeper and lasted longer, the step execution duration was shorter, and the variation of the CoM speed was lower. In other words, to regulate the speed of progression, the amputee subjects controlled the spatial and temporal parameters of the propulsive forces. In the modulation of the CoM progression velocity, when the gait was initiated with the intact limb, the amputees controlled only the intensity of the propulsive forces during both the APA and step execution phases. In contrast, when the gait was initiated with the prosthetic limb, the modulation resulted mainly from the propulsive forces generated during the step execution phase. These different strategies are discussed in terms of the subject's capacity to adapt the motor program for gait initiation to new constraints.