Exploring the impact of myotonia on daily functioning in myotonic dystrophy: a patient-reported survey

Prominent symptoms in myotonic dystrophy (DM) negatively affect the hands/arms (DM1), legs (DM2), or relate to fatigue. Myotonia is experienced by 90% of people with DM1 and is generally the DM hallmark. However, it is unclear how people with DM consistently differentiate the impact of myotonia from other symptoms - especially weakness - across the broad framework of DM.

ENSA (revEal the burdeN on daily life for myotonic dyStrophy patients due to myotoniA) was a global (targeted at eight major countries), anonymised, online, patient-reported survey to investigate perceptions of daily impact/burden of myotonia and explore antimyotonic treatment access. Thirty-two questions covering DM symptoms, broad disease impact, specific impact of myotonia and treatment formed an online survey. Internal consistency of multi-item myotonia-related domains was assessed.

N=386 (18-82 years; 62% women; 74% self-reporting a genetically confirmed DM1 diagnosis) completed ENSA. Common symptoms were hand/arm myotonia and upper-body muscle weakness (DM1, mean scores, 3.5; possible range, 1-5) and lower-body muscle weakness (DM2, mean score, 4.2; possible range, 1-5). Leg-myotonia scores increased in higher-age brackets: DM1/DM2, mean 2.86/3.71 in <40 years; >3.26/>3.97 in ≥40 years. Some respondents associated "myotonia" with DM symptoms not clinically linked to myotonia. Nevertheless, heightened "myotonia" scoring was associated with heightened daily impact/burden, and worsened abilities to undertake normal activities. Cronbach's α was 0.96 (95% CI: 0.95-0.97) and 0.93 (95% CI: 0.91-0.95) for DM1 and DM2, respectively, indicating good internal consistency for questions assessing impact of myotonia on daily activities. 193/247(78%) DM1 and 57/83(69%) DM2 respondents were not on an antimyotonic. Treatment levels were highest in Italy (37%), where greatest treatment-related improvements and lowest dissatisfaction scores were reported (mean 24.6%; mean 40.0% for the other target countries).

ENSA data indicate that neuromotor function is impaired and that myotonia is frequently burdensome in DM. Some patients have unmet treatment needs, although antimyotonic treatment may reduce the impact of myotonia and, consequently, improve aspects of daily living. Patients may need guidance to differentiate "myotonia" from other muscle symptoms. Nevertheless, ENSA enhances understanding of patient-reported symptom burden in DM and indicates support for antimyotonic treatment.