Table 2.
Common myotonic disorders and their varied features
| DM‐1 | DM‐2 | Recessive Myotonia (Becker Type) | Dominant Myotonia (Thomsen's Type) | Paramyotonia Congenita | Potassium‐Aggravated Myotonia | Hyperkalemic Periodic Paralysis | |
|---|---|---|---|---|---|---|---|
| Mutation | DMPK (dystrophia myotonica protein kinase) | ZNF9 (zinc finger protein 9) | CLCN‐1 (chloride channel) | CLCN‐1 (chloride channel) | SCN4A (sodium channel) | SCN4A (sodium channel) | SCN4A (sodium channel) |
| Muscle atrophy | Yes | Yes | No | No | No | No | No |
| Cold sensitivity | No | No | No | No | Yes | Possible | No |
| Muscle weakness | Yes | Yes | Common, with exercise, transient + improves rapidly | Uncommon | Common, exacerbated by cold, can be prolonged for several hours | No | No |
| Paradoxical myotonia | None | None | None | None | Yes | Possible | Possible |
| Systemic features | Yes | Yes | No | No | No | No | No |