Quantification of pathological gait parameter thresholds of patients with idiopathic normal pressure hydrocephalus in clinical gait analysis

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Descriptive statistics

The characteristics of NPH patients are described in Table 1. Anthropometric measurements between groups were comparable with no statistically significant differences between groups. 37 out of 55 patients (67.3%) suffered from all three symptoms of Hakim’s triad. During gait assessment, episodes of “walking stoppage while talking” were observed in 28 patients (50.9%), two patients (3.6%) presented gait blockage. No such phenomenon was present in healthy subjects. NPH patients showed reduced stride length and walking speed with an elongated double support phase, an enlarged base of support, and increased variability in stride length (see Supplementary Table 1). Over the course of the disease, 51 patients (92.7%) underwent a CSF drainage procedure. Thereafter, walking improved in 43 (78.2%) patients, cognitive improvement was observed in 37 (67.3%) patients. 31 patients (56.4%) underwent VP shunt surgery.

Table 1 Characteristics of the sample of patients with idiopathic normal pressure hydrocephalus (NPH) and healthy subjects.

Gait Parameter Thresholds During Preferred Gait Speed

The statistical approach is visualized in Fig. 1. The AUC values ​​of the classification models are shown in Table 2. The gait parameter thresholds, sensitivity as well as specificity values ​​are shown for all gait conditions in Fig. 2.

Table 2 Overview of area under the curve (AUC) values ​​of receiver operating characteristics (ROC) curves for gait parameters under different gait conditions for normal pressure hydrocephalus patient classification models idiopathic (NPH) and healthy subjects.
Figure 2

Overview of gait parameter thresholds, sensitivity and specificity values ​​of patients with idiopathic normal pressure hydrocephalus (NPH) compared to age-matched healthy subjects. Gait parameters are organized into five distinct global gait domains (x-axis). Different gait conditions are summarized into speed, sensory, and dual task (y-axis) conditions. Each tile consists of the gait parameter threshold in its unit at the top, the small numbers at the bottom indicate the corresponding sensitivity (left) and specificity (right) in %. The tiles are color coded according to the area under the curve (AUC) of the receiver operating characteristics (ROC) curve (see legend). Blue tiles illustrate that NPH patients fall below the threshold value, red tiles illustrate that NPH patients fall above the threshold value. Gray tiles indicate a non-significant regression fit. Abbreviations: Gait parameters: SLen: stride length; STime: stride time; Swing: swing phase percentage; Dsupp: double-press phase percentage; CV: coefficient of variation; ASYM: asymmetry; SWidth: stride width. Walking conditions: PS: preferred walking speed; SS: slow walking speed; MS: maximum walking speed; HR: head tilt; CE: eyes closed; DTC: Run & Dual Task Series 7; DTS: double task walking and verbal fluency; DTM: walking and carrying a dual task tray.

During speed-preferred gait, the most distinct gait thresholds were variables in the cadence domain, namely stride length ≤ 1.02 m (sensitivity 0.93, specificity 0.91, AUC 0.96 ) and a walking speed ≤ 0.83 m/s (0.80, 0.91, AUC 0.93 ). Other significant variables include Cycle variables such as swing phase ≤ 36.5% (0.93, 0.78, AUC 0.91) and double stance phase ≥ 27.0% (0.96, 0 .76, AUC 0.91) as well as variable support stride width ≥ 0.13 m (0.80, 0.91, ASC 0.89). The most distinct variability parameter was CV stride length ≥ 3.4% (0.93, 0.72, AUC 0.90). Asymmetry parameters showed insignificant to only moderate discriminating power.

Gait parameter thresholds in other gait conditions

The most notable thresholds were observed during DTS: stride length ≤ 0.97 m (0.97, 0.93, AUC 0.98), swing phase ≤ 35.1% (0.91, 0, 90, AUC 0.96), double stance phase ≥ 30.2% (0.88, 0.90, AUC 0.95), and stride width ≥ 0.13 m (0.91, 0.86, AUC 0.89). During EC, the gait threshold was ≤ 0.69 m/s (0.90, 0.91, AUC 0.96). Mean AUC values ​​of all gait conditions for each gait parameter ranged from 0.52 (stride time asymmetry) to 0.94 (stride length). Other high overall AUC values ​​were found for speed (0.92) and for the double support phase (0.91; see Table 2). Overall, the most distinct gait parameter thresholds were observed for the Rhythm, Cycle, and Assistance gait domains.

AUC values ​​and influence of gait examination conditions

Mean AUC values ​​of all gait parameters examined for each examination condition ranged from 0.76 (SS) to 0.84 (DTM). AUC values ​​for PS and HR were 0.82. The highest single AUC values ​​were found in DTS (AUC stride length: 0.98, AUC swing phase: 0.96, AUC double support phase: 0.95), DTM (AUC stride length: 0.96, AUC speed: 0.95), EC (AUC speed: 0.96, AUC double support phase: 0.95) and PS (AUC stride length: 0.96, AUC speed: 0.93) .

The most distinct dual task condition for all gait parameters was DTM with the following notable threshold parameters: gait speed ≤ 0.87 m/s (0.91, 0.87, AUC 0.95), length stride length ≤ 1.03 m (0.94, 0.89, AUC 0.96), swing phase ≤ 35.5% (0.83, 0.98, AUC 0.91), double stance phase ≥ 28.0% (0.89, 0.87, AUC 0.93), stride length CV ≥ 3.7% (0.91, 0.78, AUC 0.91) and stride width ≥ 0, 12m (0.91, 0.83, AUC 0.91).

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