To validate a novel patient reported outcome for assessment of muscle cramps, the Toronto Cramp Impact Index (TCII).

Although cramp frequency has been used traditionally to assess cramp impact, a more comprehensive measure is needed. Using patient interviews and expert input, the 16-item, 46-point TCII scale was developed. The preliminary scale underwent field testing to determine content and construct validity.

Patients with idiopathic and secondary muscle cramps were included in the study. A subgroup of patients had the index repeated at 2 weeks to assess intra-rater reliability. Cramp frequency, intensity, duration and location was collected on each patient. Comparison measures including the EQ5D, Epworth Sleepiness Scale, Beck Depression Inventory, SF6D Utility as well Sleep Impact, Sleep Disturbance, Pain Impact and Stiffness Impact were collected.

86 patients with idiopathic and secondary cramps were included. Responses were evenly distributed and missing values low for each item (0-5 for visit 1 and 0-9 for visit 2). Factor analysis suggests three distinct domains including sleep impact, cramp characteristics and impact on daily life/mental health. Cramp duration and location were not clearly related to any domain and considered for reduction. There was strong correlation between the TCII and associated comparison measures other than Pain Impact. Intra-rater reliability (n=61) showed a high intraclass correlation coefficient of 0.87 for the total score, with only one item with Kappa <0.5.

The TCII shows promise as a patient centred, reliable and comprehensive way to assess muscle cramps. The revised, final version of the TCII including performance metrics in a full validation cohort of >100 patients will be presented at the AAN meeting.