Table 1.
Screening Characteristics
| Baseline Characteristics# | Treatment Sequence | |
|---|---|---|
| Mexiletine then Placebo N=29 | Placebo then Mexiletine N=30 | |
| Age in Years - Mean (Range) | 41.1 (16–66) | 44.7 (22–68) |
| Gender: Male - No. (%) | 13 (44.8) | 20 (66.7) |
| Race: White - No. (%)◆ | 28 (96.6) | 29 (100.0) |
| Ethnicity: Hispanic - No. (%) | 4 (13.8) | 9 (30.0) |
| Medication: Mexiletine - No. (%) | 7 (24.1) | 6 (20.0) |
| Medication: Other - No. (%) | 3 (10.3) | 1 (3.3) |
| IVR – Stiffness - Mean (SD)¶ | 3.89 (2.39) | 4.63 (2.99) |
| SF-36 – Physical Norm-Based - Mean (SD) | 38.7 (9.65) | 40.8 (11.0) |
| SF-36 Mental Component - Mean (SD) | 44.5 (13.3) | 47.6 (9.8) |
| INQol – QOL Score - Mean (SD) € | 14.0 (9.03) | 15.9 (12.5) |
| Clinical Hand Opening Time in Seconds – Geometric-like Mean (pseudo SD)¥ | 1.11 (0.898, 3.48) | 0.605 (0.510, 1.84) |
| Clinical Eye opening Time in Seconds - Geometric-like Mean (pseudo SD)¥ | 0.507 (0.486, 2.42) | 0.466 (0.455, 2.31) |
| Abductor Digiti Minimi EMG grade 3+ - No. (%)¤ | 18 (62.1) | 18 (62.1) |
| Short Exercise Test (% of Baseline) - Mean (SD) £ | 78.7 (24.5) | 80.8 (28.7) |
| Tibialis Anterior EMG grade 3+ - No. (%)¤ | 20 (69.0) | 19 (65.5) |
| Quantitative Handgrip Myotonia in Seconds - Geometric-like Mean (pseudo SD)¥ | 0.651 (0.288, 0.518) | 0.507 (0.211, 0.361) |
| Mutation – Chloride - No. (%) | 17 (58.6) | 17 (56.7) |
| Mutation – Sodium - No. (%) | 10 (34.5) | 11 (36.7) |
| Mutation – No Identified Mutation – No. (%) | 2 (6.9) | 2 (6.7) |
SD = standard deviation
No. = number of participants
Reference ranges for the scales used in this study are as follows: for the interactive voice response diary (IVR) 0=no symptom, 1=’minimal, 9= ‘worst ever experienced14; SF36 Physical and Mental composite employs a linear T-score transformation 0–100 scale with US mean = 50, lower = larger impact22; the Individualized Neuromuscular Quality of Life scores are presented as a percentage of the maximum detrimental impact, a higher score indicates greater impact, with the exception of treatment effects, where a higher score indicates perceived effectiveness20; clinical hand opening time and eye opening time increase with increasing myotonia; the EMG grade ranges from 0 for no myotonia, 1+ for meeting minimal electrographic criteria for myotonia to 3+ for myotonia in every needle position19; the % of baseline on short exercise testing will decrease with increasing myotonia18; quantitative handgrip myotonia evaluation is expected to increase with increasing myotonia15.
1 participant declined reporting their race
Very few (8) participants had a true baseline report of stiffness severity. Consequently, if unreported, day 1 report was used (40) and if that was unreported, day 2 report was used (10).
1 participant missing Abductor Digiti Minimi EMG grade and Tibialis Anterior EMG grade
1 participant missing short exercise test results
1 participant missing QOL score
geometric-like mean is the inverse transformation (exp[y]−0.1) of the mean of transformed (log[t+0.1]) times. The pseudo standard deviations are the widths of the inverse transformed interval between the mean and plus/minus one standard deviation from the mean, these being calculated on the transformed scale. 8 participants did not have baseline Quantitative Handgrip Myotonia test. None were missing for the clinical tests.