Background and Aim 

About 20-30% of individuals with ASD present tip-toe behavior (TTB)[1]. We described three mutually exclusive clinical functional classes with a different degree of severity: Tip-toe Behavior (TTB) during running (TTB1), TTB during walking and running (TTB2) and TTB during standing, walking and running (TTB3)[2]. Assessing and monitoring TTB in ASD subjects is critical to identify ASD subjects at risk of developing muscle shortening, but systematic observations of the natural history of TTB in ASD sub using standardized assessment are lacking. The aim of this prospective cohort study is to describe the natural history of TTB and NO-TTB ASD subjects at short-medium term. 

Methods 

The inclusion criteria were: an ASD diagnosis according to the DSM V criteria and a diagnosis confirmation based on the ADOS2. The exclusion criteria were: presence of co-morbid diagnoses that would have an impact on gait. The prospective study included 72 consecutive subjects (62 males; mean age: 15,68 years – SD 3,85) present in our Institute. The assessment of presence/absence of TTB during standing, walking and running was done using a standardized assessment[2]. We repeated the same evaluation 12 to 44 months (mean: 29,88 months – SD 8,86; median: 34,5 months) after the first observation. 

Results 

During the first TTB assessment 49 subjects resulted Non-TTB (68,1%) and 23 resulted TTB. In TTB group, 4 subjects were TTB1, 9 subjects were TTB2 and 10 subjects were TTB3. At follow up 7 out of 23 TTB subjects (30%) changed the severity class, 5 decreasing and 2 increasing severity (table 1). No one shifted to NO-TTB group. In NO-TTB group 8 subjects (16%) shifted to TTB group (5 in TTB 1 class, 2 in TTB 2 class and 1 in TTB class 3. The ADOS calibrated severity score of the converters was not different from non-converters (7,5 – 1,4 SD versus 7,56 – 1,74 SD). 

Conclusions 

TTB behavior can change over time in ASD subjects. In an average time of two years 30% of TTB subjects change their severity class and 16% of Non-TTB subjects become TTB. This finding underlies the importance of close monitoring of TTB with standardized protocols. 

Notes:

1 Autism Research Unit, Villa Santa Maria Foundation, Tavernerio (Como), Italy
2 School of Medicine and Surgery, University of Milano Bicocca, Milan, Italy