# Portable RGB-D Camera-Based System for Assessing Gait Impairment Progression in ATTRv Amyloidosis
## 4 Discussion
The third patient (P3) showed only weakness at the toes from one assessment moment to the other. This patient was in stage I of the PND and ATTRv amyloidosis scores and therefore showed fewer restraints overall during gait when observed by the neurologist. Nevertheless, the quantitative analysis for this patient performed with the reference system showed a significant difference from T0 to T1 for half of the gait parameters (seven out of fifteen spatiotemporal, and four out of eight kinematic), which again shows that a quantitative analysis may help detect changes in gait that are not visible to the naked eye. The significant changes were correctly detected by the RGB D camera for six out of eleven parameters, which also correctly detected no significant changes for 7 out of 12 parameters. It is important to notice that patient P3 began taking tafamidis ten months before the first assessment. Although the clinical observation is in line with the finding that there is a higher efficacy of the drug at the earliest stage of ATTRv amyloidosis [12], the quantitative analysis showed significant changes for several gait parameters. Therefore,the obtained results suggest that the introduction of an objective tool for gait analysis of ATTRV amyloidosis patients may also benefit drug efficacy evaluation. Regarding the fourth patient (P4), most spatiotemporal parameters showed no significant difference (11 out of 13 analyzed parameters). However, actual significant changes were observed for only a few parameters (two out of thirteen spatiotemporal, and three out of eight kinematic), which is in line with this patient's clinical observation (no alteration of MRC scores between T0 and T1). Nonetheless, P4 suffered a major worsening in the appointment that followed the data collection at T1. Therefore, the significant changes detected with the reference system may have been an anticipation of that evolution, although this is speculative. The clinical assessment of the fifth patient (P5) showed a slight worsening of dorsif flexion (four to three score on the MRC scale, from T0 to T1), which led to a discrete yet observable worsening of gait (steppage was very low at T0 and clear at T1--see Table 2). Despite the observed worsening of dorsiflexion, the actual difference between T1 and T0 for the ankle angle range is not significant. However, other gait parameters had significant changes (stance and double support duration decreased, while stride length, gait speed, foot swing velocity, maximum and minimum elbow angle, and maximum knee angle increased), which may be related to the prominence of the steppage profile at T1. The RGB-D camera correctly detected significant changes for six out of eight parameters and non-significant changes for eight out of eleven parameters. For the sixth patient (P6), gait did not change in clinical observation. However, the distal segmental force in dorsiflexion and plantar flexion showed worsening between T0 and T1, which may explain the differences found for some quantitative gait parameters (six out of thirteen spatiotemporal, and five out of eight kinematic). Although the analyzed parameters do not have a direct relation with those used for clinical observation, the alterations measured quantitatively are consistent with the observed progression. Regarding the RGB-D system, it correctly detected significant or non-significant changes for 11 parameters in the case of P6. Note that TBCM-ML was either not analyzed for some patients (P4, P5, P6) or the difference between T0 and T1 was not significant (P1, P2, P3). In contrast, TBCM-V was found to be significantly different for one patient (P1). This suggests that the vertical alterations in ATTRv amyloidosis gait are higher than mediolateral ones, which seems to follow the visual indication of the importance of the absence of dorsiflexion and the consequent rise of the knee for a safe foot-landing, in steppage.