SMA CLINICAL DATA, OUTCOME MEASURES AND REGISTRIES: P.79The relationship between function and muscle strength in the upper limb in a cohort of children with spinal muscular atrophy type II and III – a prospective study

Abstract

The upper limb (UL) function in SMA patients has been studied using different functional scales and assessment tools but there are limited data on hand function and endurance. The purpose of this study was to determine what are the relationships between UL function and the muscle strength and fatigability of the hand in children with SMA type II and III. Data were collected at one baseline evaluation when 6 girls and 4 boys (mean age 8 years, range 5. 2 – 10. 9), five with SMA II and five with SMA III (3 ambulant) took part in the study. To evaluate upper limb function we used the validated Revised Upper Limb Module (RULM); to measure hand grip, thumb pinch strength, and hand function and fatigue we tested the dominant side using the Myotools set (MyoGrip, MyoPinch and Moviplate), recently developed to assess upper limb strength and function in neuromuscular patients. The MyoGrip and MyoPinch have previously been reported to have a significant correlation with clinical severity determined by the MFM scale. In our cohort the average Brook functional score was 4.9 (range from 3 to 6). The RULM total score showed a strong correlation with the average of the three best Myotools scores for hand grip and thumb pinch (Pearson `r' = .894, (95% CI .779 to .974) and .858 (95% CI .720 to .981) respectively) but only ``moderate to low'' correlation when hand fatigue was measured with the MoviPlate (r = .423, 95% CI -.183 to .960). There was no significant correlation between the MoviPlate and the MyoGrip, or the MyoPinch total scores ('r' = .467; 95% CI.-.329 to .951; and 'r' = .314; 95% CI -.437 to .939). In this ongoing study, we showed for the first time that the RULM score correlates with muscle strength of the hand but not with fatigue. Although these preliminary data indicates a trend towards an association between function and power in the upper limb of SMA children, to support our findings we intend to investigate the longitudinal effect in a bigger SMA cohort.