Nine Hole Peg Test asymmetry in refining upper limb assessment in multiple sclerosis

The Expanded Disability Status Scale (EDSS) is the most frequently used scale to measure neurologic impairment and quantify the level of disability in Multiple Sclerosis (MS) even though the scale focuses on ambulation and undervalues upper limb (UL) impairment. The 9-Hole Peg Test (9-HPT) is the gold standard for UL assessment in MS, calculating a mean score from right and left arms, even though subjects with MS often show a lateralization of neurological deficit.

The study aimed to determine whether an interaction exists between mean right-left 9-HPT scores or 9HPT score asymmetry (difference between right and left side) in predicting EDSS in MS subjects.

Demographic and disease variables and 9-HPT scores were obtained from medical records of individuals with MS collected in an ad-hoc database. Subjects with 9-HPT score ≤180 s for each arm were included. An asymmetry score was represented as the absolute value of the difference between 9-HPT scores for both arms.

549 subjects were included: 67.8% female, mean age 45±13.14 years, mean EDSS 3.98±2.12, 356 relapsing-remitting, 68 primary and 125 secondary progressive, mean 9-HPT scores: right arm 30.20 ± 19.99 s, left arm 31.80 ± 20.35 s. Mean asymmetry was 9.35±18.20 s. Correlation between mean right-left 9-HPT scores and EDSS was 0.58 (p<.001). Significant interaction between mean right-left 9-HPT scores and 9-HPT asymmetry in predicting EDSS scores was found. Regression slope of EDSS on mean right-left 9-HPT score decreases as asymmetry value increases (non-significance area values ≥ 40.93 s).

Findings suggest interaction exists between mean right-left 9-HPT scores and asymmetry in predicting EDSS. A consequence of this is that, by disregarding information about asymmetry, studies exploring the association between mean right-left 9-HPT scores and global measures of disability may provide biased results. The bias tends to increase as asymmetry increases, and to be most prevalent among patients with EDSS scores > 6.