Circular Timed Up and Go (cTUG) for Ataxia: Development and Validation

Background What is Cerebella ataxia (CA)? Cerebellar ataxia (CA) is a collection of signs and symptoms caused by cerebellar dysfunction, which can be the result of different disease processes including hereditary and acquired conditions (Hadjivassiliou et al., 2017).

Common clinical presentation of CA patients includes balance and gait dysfunction, dysmetria, dyssynergia, dysarthria and dysdiadochokinesia (Diener \& Dichgans, 1992). People with CA usually walks with increased step width, increased foot rotation angles and reduced cadence, which is related to impaired balance (Stolze et al., 2002). Marsden \& Harris (2011) suggested that the high incidence of falls in people with CA may be related to their poor balance in walking. Therefore, it is crucial to assess the balance of people with CA to identify potential fallers.

Current balance assessments and drawbacks of TUG There are some clinical tests commonly used for assessing the balance of people with CA, including both generic measures of balance and ataxia-specific rating scales. The current best balance outcome measures for CA includes Berge Balance Scale (BBS), Timed Up and Go test (TUG), and the balance related items in Scale for the assessment and rating of ataxia (SARA) (Winser et al., 2015). TUG is commonly used in clinical settings for the assessment of mobility and fall risk of individuals (Dawson et al., 2018). However, a study done by Winser et. al (2017) found that the correlation between TUG and ataxia rating scales (SARA and ICARS) is only moderate. This indicates that the gait speed and functional mobility findings of TUG might not truly reflect the balance deficits of CA. Therefore, in order to bridge this gap, our study will develop a modified TUG for the assessment of balance in people with CA. The specific objectives of this study will be to examine the reliability, validity of the modified TUG for identifying the balance and fall risk of cerebellar ataxia patients.

Circular TUG: A modification that might suit CA Circular TUG (cTUG) is a modified version of the standard TUG. cTUG is an equilibrium test that challenges subjects' ability to maintain balance in response to constant change in direction of walking. In standard TUG, the person gets up from an armchair, walks three meters in a straight pathway, then turn 180 degrees and walks back to the chair to sit down (Podsiadlo \& Richardson, 1991b). However, in cTUG, the subject walks a semi-circular pathway instead of a straight line. Walking in a circular pathway targets at challenging the coordination of people with CA as walking in a circle requires constant change in directions and correction after feedback (Goodworth et al., 2012). Moreover, walking in a circle is more difficult for patients with CA as it increases the role of the cerebellum for trunk and foot control during curvilinear locomotion (Goodworth et al., 2012). Therefore, it is speculated that the cTUG will have better accuracy in predicting the balance and falls risk among people with CA.

Objectives and hypothesis The overall aim of this study is to develop and test the psychometric properties of the cTUG in assessing balance and falls risk prediction among individuals with cerebellar ataxia and age-matched healthy volunteers. To address this objective, we have the following specific objectives.

1. Develop the cTUG and record the normative scores of the newly developed scale among healthy volunteers and mean scores among individuals with cerebellar ataxia.
2. Examine the test-retest, inter-rater and intra-rater reliability of the cTUG among healthy volunteers and individuals with cerebellar ataxia.
3. Examine the concurrent validity, convergent validity, discriminant validity, and external validity of the cTUG among individuals with cerebellar ataxia.

For validity, concurrent validity, convergent validity, discriminant validity, and external validity will be assessed. Based on the findings of a previous study that reported a moderate negative correlation (-0.62) between standard TUG and Berg Balance scale (BBS) (Cattaneo et al., 2006), we hypothesize a moderate to strong negative correlation between cTUG and BBS.

Moreover, based on the findings of a previous study that reported a moderate positive correlation (0.584) between standard TUG and Scale for the Assessment and Rating of Ataxia (SARA) (Choi et al., 2018), we hypothesize a moderate to strong positive correlation between cTUG and the balance component SARA.

In addition, based on the findings of a previous study that reported a positive correlation between TUG and Modified Clinical Test of Sensory Organization and Balance (m-CTSIB) and a negative correlation between TUG and Limit of Stability (LOS) (Dawson et al., 2018), we hypothesize a positive correlation between cTUG and Sensory Organization Test (SOT), and a negative correlation between cTUG and LOS.

Besides, based on the findings of a previous study that reported a moderate negative correlation (-0.78) between standard TUG and Barthel Index (BI) (Podsiadlo \& Richardson, 1991b), we hypothesize a moderate negative correlation between cTUG and BI.

For reliability, intra-rater reliability and inter-rater reliability will be assessed. Repeat assessment by the same investigator will be used to estimate intra-rater reliability and repeat assessments by 2 different investigators will be used to estimate inter-rater reliability. All the assessments will be completed on the same day with each assessment conducted with 1 hour rest period.

Ethics will be obtained through the Human Subjects Ethics Sub-committee of the Hong Kong Polytechnic University and trial registration will be done through the Clinical Trials Registry. Participants with a confirmed diagnosis of CA of any or unknown cause will be recruited through the Hong Kong Spinocerebellar Ataxia Association (HKSCAA) and one group of age-matched healthy volunteers will be recruited from the Hong Kong PolyU campus. We will post advertisement flyers at the HK PolyU campus and at the HKSCAA for recruiting potential participants. In addition, for recruiting participants with cerebellar ataxia, an advertisement flyer will be posted on the monthly newsletter of the HKSCAA. The specific criteria for recruitment are reported elsewhere.