Because handedness non-right-handedness (NRH) is associated with increased incidence of other auto-immune disorders, Shirani et al. (2019) suggested NRH might be associated with MS. In 9,618 individuals with MS, no differences were reported between left- versus right-handers (LH vs RH) in age at diagnosis, MS type, or patient determined disease steps (PDD) score. Crucially however, left- versus right-handedness was not defined, and it is not clear how this categorization was determined. There is now evidence that direction of hand preference (LH vs RH), is less important in examination of cognitive, behavioral, and neuroanatomical measures than is degree of handedness (consistent- versus inconsistent-handedness).
Objectives: To better characterize MS-handedness relationships, using measures of both handedness direction and degree.
After IRB approval, recruitment was via social media relevant to MS, from November 2019 to May, 2020 (22 men, 116 women). The EHI ranges from -100 (perfectly consistently-left-handed, CLH) to +100 (perfectly consistently-right-handed, CRH), and can be used to examine both direction and degree of handedness. Three measures of handedness: a. Writing Hand (WH): Classification based on answer to Which hand do you write with. Any score not always right, was considered left-handed (LWH); always right was right-handed (RWH). Direction: Scores at and below 0 were LH; scores above 0 were RH. Degree: Scores +80 and above were CRH, scores -80 and below CLH, and scores -75 and to +75 inconsistently-handed (ICH). Testing was completed via Qualtrics, and included the EHI, PDD, gender, current age, and length of diagnosis.
Results revealed significantly younger age at diagnosis in ICH (m = 34.74 se = 1.70, p<.05) compared to CRH (m=38.83, se=1.14). In women only (see Discussion, n=116), an effect of LH versus RH on MS type (chi-square =4.56, P<.05) revealed of 11 LH women, 2 reported PPMS, while of 105 RH women, 2 reported PPMS. Conclusions: Gardener et al. (2009) reported 62% elevated risk of MS in female nurses who reported being left-handed. LH women here had an elevated risk of more severe MS than right-handed women; gender effects may interact with MS likelihood and severity as a function of handedness. Younger age at diagnosis in ICH versus CRH is novel, and warrants further examination. Non-right-handedness may be associated with increased MS severity, either in earlier diagnosis or MS typology, especially in women.