Myotonia Dystrophica (Myotonic Dystrophy, Steinert Disease)

Incidence of approximately 1:8000.

Incidence of the congenital form is higher, with an incidence of 1:100,000 compared with adult-onset form.

Operative/anesthetic and postop morbidity and mortality are increased and not proportional to severity of disease.

High incidence of cardiopulmonary complications, including sudden death, cardiac failure, and cardiomyopathy.

Increasing frequency of symptoms

Signs of respiratory or cardiac decompensation

Degenerative disease of skeletal muscles. It consists of a triad of characteristic features, including frontal baldness, cataracts, and mental retardation.

It can be variable in presentation. Some are asymptomatic, whereas more severe congenital manifestations include mental retardation and respiratory insufficiency.

Typically the onset of symptoms in second and third decades of life with progressive muscular weakness and wasting, most common in the cranial and distal limb muscles (e.g., temporalis and masseter muscle atrophy, known as “hatchet face” and “limb muscles”). There may be diminished deep tendon reflexes and muscles of the vocal cord apparatus resulting in nasal speech. A proximal muscle variant has recently been recognized. Death frequently occurs in the fifth or sixth decade of life and is usually related to cardiopulmonary complications, including sudden death from conduction abnormalities, cardiomyopathy, and/or CHF.

There is often persistent contracture after cessation of stimulation or voluntary contraction of the muscle. This inability of the skeletal muscle to relax is diagnostic. EMG is corroborative and pathognomonic and it shows continuous low-voltage activity with high-voltage, fibrillation-like potential bursts.

Myotonic dystrophy is an intrinsic disorder of skeletal muscle linked to a myotonin-protein kinase gene on chromosome 19q13.2. A defect in Na ⁺ and Cl ⁻ channel function produces electrical instability of the muscle membrane and self-sustaining runs of depolarization. Abnormal metabolism of calcium may be seen.

Myotonic dystrophy is inherited via an autosomal dominant trait. It occurs from an abnormal expansion of the nucleotide CTG on chromosome 19, which codes for a serine-threonine protein kinase. Variable gene expressivity can be seen within the same family in which one member can have minimal affects and another be severely affected. Anticipation is seen with inheritance, and the longer the CTG repeat, the more severe the disease is.