# Portable RGB-D Camera-Based System for Assessing Gait Impairment Progression in ATTRv Amyloidosis
## 4 Discussion
By analyzing the follow-up results considering only the actual values (i.e., obtained with the reference system) at the two different assessment moments, we found that the parameters that evolved less overall (i.e., the difference was not significant for half or more patients) were step, swing, single and double support duration, stride length, step length and width, gait speed and its variability, foot and arm swing velocity, TBCM-ML, minimum elbow angle, minimum and maximum knee angles, as well as hip and ankle angle range. There was a significant increase from T0 to T1 in the case of the spine middle angle, as well as the maximum and minimum elbow and knee angles, for most patients. This increase may have occurred because of a search for balance, which translated into a widening ofthe movements' amplitude. On the contrary, there was an overall significant decrease in the spine shoulder angle, suggesting that the patients tend to shorten their distance to the ground and lower their center of mass to increase balance, probably due to steppage. The tendency of wider steps and lower double support duration may have also contributed to that decrease. Step length and width are important to consider if there are alterations to the walking base (i.e., the distance between the lower limbs) to increase walking stability [23]. In this sample, both step length and step width decreased for the patients who have a significant change in this parameter. The biggest challenge in performing a detailed analysis of the gait of ATTRv amyloidosis patients is the complex context of this multisystemic condition. Therefore, we also performed a more clinically focused analysis of the intra-patient gait evolution, where we compared the obtained quantitative results with the qualitative scores obtained through clinical observation (presented in Table 2). For the first patient (P1), the actual difference between T0 and T1 was not significant in the case of the ankle angle range. This result is in line with the clinical observation of P1's specific disease progression, which showed only small dorsiflexion worsening from 4 to 4--(see Table 2). In contrast with the reference system, the RGB-D camera-based system detected a significant change for the considered parameter. However, the same system was able to correctly detect non-significant or significant differences for most spatiotemporal parameters (12 out of 15) and five kinematic parameters (spine shoulder and spine middle angles, maximum and minimum knee angles, and hip angle range). For the second patient (P2), the worsening profile is discrete, as was the case with P1. This patient already had a profound distal motor deficit that worsened with the loss of plantar flexion. Moreover, at T1, a proximal deficit was noticed through the loss of muscular force and consequent loss of knee flexion ability. However, in contrast with the qualitative analysis, the quantitative results show an actual significant increase in the maximum and minimum knee angles, which suggests that quantified motion information provides information that may be difficult to obtain through observation only. Nevertheless, the RGB-D camera was not in agreement with the reference system for the knee angle parameters. Although no changes regarding dorsiflexion were observed clinically in P2, plantar flexion worsened (1 to 0). The latter was translated into a significant decrease in the actual ankle angle range. Despite the difference measured for the RGB-D system not being statistically significant, the mean difference value was similar to that obtained with the reference system (\(-5\) and \(-7\) degrees, respectively). The worsening of plantar flexion may have contributed to a significant increase in stride, step, stance, swing and single support duration, and a significant decrease in stride and step length, gait speed, gait speed variability, and foot swing velocity. These significant differences were correctly detected by the RGB-D system for all these parameters, except swing and single support duration, and step width.