Extrapyramidal signs in normal pressure hydrocephalus: an objective assessment

Abstract

Background: Beyond the classic Normal Pressure Hydrocephalus (NPH) triad of gait disturbance, incontinence, and dementia are characteristic signs of motor dysfunction in NPH patients. We used highly sensitive and objective methods to characterize upper limb extrapyramidal signs in a series of NPH subjects compared with controls. Concentrated evaluation of these profound, yet underappreciated movement disorders of NPH before and after techniques of therapeutic intervention may lead to improved diagnosis, insight into pathophysiology, and targeted treatment.

Methods: Twenty-two (22) consecutive NPH patients and 17 controls performed an upper limb motor task battery where highly sensitive and objective measures of akinesia/bradykinesia, tone, and tremor were conducted. NPH subjects performed this test battery before and more than 36 h after continuous CSF drainage via a spinal catheter over 72 h and, in those subjects undergoing permanent ventriculo-peritoneal shunt placement, at least 12 weeks later. Control subjects performed the task battery at the same dates as the NPH subjects. Statistical analyses were applied to group populations of NPH and control subjects and repeated measures for within subject performance.

Results: Twenty (20) NPH subjects remained in the study following CSF drainage as did 14 controls. NPH subjects demonstrated akinesia/bradykinesia (prolonged reaction and movement times) and increased resting tone compared with controls. Furthermore, the NPH group demonstrated increased difficulty with self-initiated tasks compared with stimulus-initiated tasks. Following CSF drainage, some NPH subjects demonstrated reduced movement times with greater improvement in self- versus stimulus-initiated tasks. Group reaction time was unchanged. Resting tremor present in one NPH subject resolved following shunt placement. Tone measures were consistent for all subjects throughout the study.

Conclusion: Clinical motor signs of NPH subjects extend beyond gait deficits and include extrapyramidal manifestations of bradykinesia, akinesia, rigidity, and propensity to perform more poorly when external cues to move are absent. Objective improvement of some but not all of these features was seen following temporary or permanent CSF diversion.

Figure 1

Reaction time in NPH. Plot of Reaction times to movement onset (RT/MO) for each NPH subject at baseline (gray bars) and following CSF removal (black bars; n = 45). Data are median values ± standard deviation in s. No significant differences were demonstrated in NPH RTs following CSF drainage via a temporary spinal catheter (nor later by VP shunt). Vertical arrows indicate those NPH subjects who later underwent shunt placement.

Figure 2

Movement time in NPH. Plot of stimulus-initiated (gray bars) and self-initiated (black bars) movement times (MT) of each NPH subject at baseline in s (mean ± SEM; n = 45). A subset of subjects demonstrated statistically prolonged movement times during the self-initiated tasks compared with stimulus-initiated tasks. Vertical arrows indicate those NPH subjects who later underwent shunt placement.

Figure 3

Combined movement time in control and NPH subjects. Plot of mean combined movement times (s) of all Control and NPH subjects at baseline and at a time following CSF drainage in NPH subjects with controls retested at the same time (means ± SEM). As a group, NPH subjects were bradykinetic compared with controls and demonstrated greater disparity between self- and stimulus-initiated movement times. As a group, no significant improvement was seen in MTs following CSF drainage in NPH subjects, but repeat measures analysis demonstrated significant improvement in a subgroup.

Figure 4

Self-initiated movement in NPH. Raw data plots of the 12 NPH patients who received V-P shunt during self-initiated movement time (MT) tasks. The Y axis represents time in s, separate patients are plotted on the X axis with MT from baseline measure (gray squares) and following V-P shunt placement (open circles). Those subjects that demonstrated changes in MTs (whether prolonged or decreased) with CSF drainage, demonstrated similar changes from baseline. (For comparison, average control self-initiated movement times were 513 ± 18 ms).

Figure 5

Tone analysis in NPH versus control subjects. Plots of the slope of the line of force: angular displacement about the elbow (stiffness constant k) for control and NPH subjects at baseline during repose. Solid diamonds represent each individual subject, and horizontal lines denote mean values. As a group, NPH patients displayed significantly increased tone versus controls (p < 0.02) with a majority of subjects demonstrating tone outside the range of controls.