Quantitative Assessment of TIP-TOE Behavior in Autism Spectrum Disorder: A Prospective Cohort Study

Background: About 20-30% of ASD individuals display toe-walking to some degree. Previously, using a qualitative structured assessment, we described three mutually exclusive clinical functional classes: tip-toe behavior (TTB) during running (TTB1), TTB during walking and running (TTB2) and TTB during standing, walking and running (TTB3). In another study, we also found a positive relationship between the presence and severity of TTB and the Achilles’s tendon shortening in ASD subjects. To our knowledge, no prospective quantitative TTB study is currently available.

Objectives: The aim of this prospective cohort study is to describe the natural history of TTB and NO-TTB ASD subjects at short-medium term using a quantitative standardized method.

Methods: We included 37 consecutive subjects (32 males; mean age: 12.32 years – SD 4.36) with ASD diagnosed according to the DSM V criteria, and then confirmed with ADOS–2. According to the qualitative assessment, 21 ASD subjects resulted NO-TTB, 2 resulted in TTB1 subgroup, 7 in TTB2 subgroup and 7 in TTB3 subgroup. The intensity of TTB expression during static and dynamic tests was quantified as a percentage of time spent on the tip toes and as a percentage of toe steps, respectively, through a standardized method previously described. The second assessment was repeated 11 to 38 months (mean: 21.41 months – SD 6.82; median: 23 months) after the first observation.

Results: The overall ADOS CCS was 6,67 (1,43 SD) in NO-TTB, 10 (SD 0) in TTB1, 7,57 (2.07 SD) in TTB2 and 8,29 (1,25 SD) in TTB3 (p = 0.014 between groups). The mean percentage time spent on the tip-toes (TSTT) during the static quantitative test in NO-TTB group, TTB1 TTB2, TTB3 was 0.1% (0.3 SD) , 0.5% (0.71 SD), 4.86% (6.36 SD), 29% (25.15 SD) respectively. The values of TSTT registered in No-TTB group and in TTB1 group remained substantially unchanged at follow up. Five subjects of TTB2 group decreased and two increased their TSTT respectively. The same happened in TTB3 group. The mean percentage of toe steps (PTS) during the dynamic quantitative test in NO-TTB group, TTB1 TTB2, TTB3 was 0.91% (2.36 SD), 3.5% (4.95 SD), 18.71% (6.36 SD), 48.71% (33.74 SD) respectively. The PTS registered in No-TTB group and in TTB1 group remained substantially unchanged at follow up. Five subjects of TTB2 group decreased and two increased their PTS respectively while four subjects of TTB3 group decreased and three subjects increased their PTS in TTB3 group.

Conclusions: This is the first study that used a quantitative structured assessment to describe change over time in TTB of ASD subjects. NO-TTB and TTB1 subgroups substantially maintained their condition at follow up. TTB2 and TTB3 subgroups showed a more variable behavior: some subjects decreasing TTB over time as commonly known, but some increasing TTB. This finding underlies the importance of a TTB sub-classification and a close monitoring with quantitative standardized protocols of TTB phenomenon.