Myotonia work-up

Screening tests

Drug screening

Serum electrolytes, glucose, calcium/phosphorus, magnesium, lactate, pyruvate, liver and thyroid function tests, blood gasses

Serum CK, aldolase, myoglobin, HbA1c, oral glucose tolerance test

CBC, ESR

EMG, NCVs, FSH (DM2) 

Anti-GAD₆₅ antibodies

Ophthalmology (slit lamp)

ECG, Echocardiogram

Specific investigations

Assays

Glycogen debrancher enzyme activity in WBC or muscle or liver biopsy specimens.

Genetic testing

DNA testing for dystrophin Xp21.2 gene deletion (from WBC or muscle tissue (50 mg)), DMPK gene for DM1, DM2 gene for DM2 (PROMM), dysferlin gene (Miyoshi DMD), CLCN1 gene (Becker and Thomsen myotonia), SCN4A gene (paramyotonia congenita), EDMD (mutation emerin gene locus Xq28) or mutation lamin A/C gene locus 1q21.2-q21.3)

Muscle biopsy: one specimen for hematoxylin & eosin, one specimen for histochemistry (fresh sample), one specimen for EM (in glutaraldehyde) and one specimen for biochemistry and genetics (fresh sample)

helpful for differential diagnosis between acid maltase and debrancher enzyme deficiency, hypokalemic polymyopathy, mitochondrial myopathy, carnitine myopathy, FSHMD, LGMD CCM, nemaline myopathy: should include in addition to specific histochemical stainings, hematoxylin & eosin, modified Gomori trichrome staining (CCM, nemaline myopathy), ATPase stain, NADH-trazolium reductase and staining for dystrophin protein (immunostaining and immunoblot, or ELISA).

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