Anesthesia for myotonic dystrophy

Published on 07/02/2015 by admin

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Last modified 07/02/2015

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Anesthesia for myotonic dystrophy

Joseph J. Sandor, MD

Myotonia—the repetitive firing of muscle action potentials causing prolonged muscle contractions even after mechanical stimulations to the muscles have ceased—is a hallmark of myotonic dystrophy. The grip test is a quick and easy way to determine the presence of active myotonia. Patients with myotonic dystrophy are unable to relax the muscles of the hand after forming a fist.

Myotonic dystrophies are autosomal dominantly transmitted disorders and classified as DM1 (Steinert disease) or DM2 (proximal myotonic myopathy), with DM1 further subdivided by age of onset. Prominent features of classic DM1, the most common myotonic dystrophy, include slowly progressive muscle weakness (dystrophy), cataracts, endocrine disturbances, and functional abnormalities of the cardiorespiratory system and gastrointestinal tract (Table 209-1).

Table 209-1

Genetics of Myotonic Dystrophy

	Type
Feature	DM1	DM2
Alternative name	Steinert disease	Proximal myotonic myopathy
Chromosome	19q13.3	3q21
Defect Gene Repeat	DMPK CTG	ZNF9 CCTG

An abnormality in the intracellular adenosine triphosphate (ATP) system that fails to return calcium to the sarcoplasmic reticulum is the theoretical pathologic mechanism of the myotonia. Contractions are not relieved by nondepolarizing neuromuscular blocking agents (NMBAs), regional anesthesia, or deep anesthesia; however, infiltration of local anesthetic agents into involved muscle may produce relaxation. Depression of rapid sodium flux into muscle cells by the use of phenytoin, procainamide, quinine, tocainide, or mexiletine may alleviate contractions by delaying membrane excitability.

Coexisting organ system dysfunction

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