Pathologies in which myotonia is isolated and generally associated with muscle hypertrophy.

Different types have been identified:

-        the congenital myotonias: (Thomsen disease if autosomal dominant transmission, Becker disease if autosomal recessive transmission) (see these terms): channelopathy due to a mutation of the CLCN1 gene (7q35)

-        the congenital paramyotonia: channelopathy of the Nav1.4 sodium channel due to a 'gain of function' mutation of the SCN4A gene (17q23-25)

-        the so-called potassium-aggravated myotonias channelopathies of the Nav1.4 sodium channel due to a 'gain of function' mutation of the SCN4A gene (17q23-25): myotonia fluctuans, myotonia permanens and acetazolamide-responsive myotonia

-        the familial periodic hyperkalemic paralysis, also caused by a 'gain of function' mutation of the SCN4A gene (17q23-25),  sometimes associated to myotonia

-        the SNEL syndrome, often considered as a form of myotonia permanens

-        the Schwartz Jampel syndrome

Anesthetic implications:

see the specific files

References : 

-        Farbu E, Softeland E, Dindoff LA. 
Anaesthetic complications associated with myotonia congenita: case study and comparison with other myotonic disorders. 
Acta Anaesthesiol Scand 2003; 47: 630-4. 

-        Stunnenberg BC, LoRusso S, Arnold WD, Barohn RJ, Cannon SC et al.
Guidelines on clinical presentation and management of nondystrophic myotonias.
Muscle Nerve 2020; 62:430-44.

Updated: January 2021