myotonia SCN4A-related (MYOSCN4A); myotonia permanens; myotonia fluctuans

Introduction

includes myotonia permanens & myotonia fluctuans

Genetics

• associated with defects in SCN4A

Clinical manifestations

• phenotypically highly variable myotonia aggravated by K+ loading, & often by cold
• myotonia permanens:
  • myotonia is generalized
  • hypertrophy of the muscle, particularly in the neck & the shoulder
  • attacks of severe muscle stiffness of the thoracic muscles may be life threatening due to impaired ventilation. In
• myotonia fluctuans:
  • muscle stiffness may fluctuate from day to day
  • provoked by exercise

More general terms

• myotonic disorder

Database

• OMIM: https://mirror.omim.org/entry/608390