• Distal-to-proximal weakness is the most common progression pattern, although myotonia and stiffness may occasionally predominate. The inheritance is autosomal dominant. Predominant cardiac involvement is by fatty degeneration and fibrosis of specialized cardiac conductive tissue (sino-atrial and atrio-ventricular nodes and His-Purkinje system.) This makes dysrhythmias the most common cardiac pathology accompanying myotonic dystrophy.
  • Muscular dystrophy (MD) has historically been diagnosed and categorized based on the age of onset, affected muscle groups, and genetic inheritance. Nearly one-third of new cases are spontaneous mutations, but two-thirds are inherited. Duchenne’s is by far the most common form of MD and is due to abnormal and deficient dystrophin; other forms of MD may involve other myocyte proteins. Administration of a depolarizing muscle relaxant to a patient with MD would be likely to cause a massive potassium release that could precipitate cardiac arrest due to hyperkalemia. MD patients, especially those with Duschenne’s type, are susceptible to malignant hyperthermia and therefore the use of triggering agents such as depolarizing muscle relaxants (succinylcholine) and halogenated potent volatile anesthetics should be avoided. A nitrous oxide/opioid (“nitrous/narcotic”) anesthetic technique would be appropriate for such a patient.