A 13-year-old girl with a history of myotonic dystrophy presents for cholecystectomy for gallstones. She has dysphagia and gastroesophageal reflux disease, and a history of dysrhythmia for which she takes procainamide.
The physical examination showed bilateral ptosis, facial weakness, and markedly decreased strength in distal extremities.
Myotonic dystrophy, also known as Steinert’s disease, is an autosomal dominant neuromuscular disorder characterized by sustained skeletal muscle contractions in response to stimulation. This is thought to be caused by abnormal chloride conductance in the muscle membrane, and by decreased inactivation of sodium channels. Myotonic episodes can be triggered by pain, stress, cold, and shivering. Myotonic dystrophy occurs in roughly 5 per 100 000 births and can be congenital (the most severe form), early-onset juvenile (usually in the second decade of life), adult-onset, or late-onset asymptomatic. Neonates with congenital myotonic dystrophy frequently present with hypotonia, difficulty feeding, and respiratory distress, and have an associated high mortality; the physical examination typically shows facial weakness, a tent-shaped mouth, and talipes equinovarus. Patients with juvenile myotonic dystrophy may exhibit delayed motor and speech milestones, but signs and symptoms of true muscular degeneration and weakness may not become apparent until after the age of 10. Myotonic dystrophy tends to involve multiple organ systems; common symptoms include cataracts, developmental delay, cardiac conduction abnormalities, aspiration pneumonia, insulin resistance, and thyroid problems.
Preoperative evaluation should include a detailed history of any neurologic deficits, as well as any comorbid conditions. A history of dysphagia and/or frequent aspiration may predict postoperative respiratory complications, and a chest x-ray may be warranted in this setting. At a minimum, this patient should have a baseline electrocardiogram, and a preoperative echocardiogram and/or cardiology consultation may be helpful.
Patients with myotonic dystrophy often have cognitive impairment and may display fear and anxiety preoperatively, which may in itself trigger a myotonic episode. However, patients are very sensitive to the respiratory depressant effects of drugs such as benzodiazepines and opiates. Therefore, premedication with an anxiolytic such as midazolam is controversial, and the risks and benefits must be weighed by the anesthesiologist. Premedication with an antacid is reasonable, particularly in patients with a history of aspiration.
This patient is taking procainamide, which increases the duration of action of muscle relaxants and antagonizes the effects of neostigmine. Procainamide also can potentiate the risk of ventricular arrhythmias in the setting of antihistamines and beta blockers.
Place external pacer/defibrillator pads prior to the induction of anesthesia.
Consider placement of an arterial line for assessment of adequate oxygenation and ventilation.
Consider rapid-sequence induction, especially if there is a history of aspiration; however, succinylcholine should be avoided, both because of the possibility of masseter spasm and/or a myotonic episode and because of a possible exaggerated hyperkalemic response due to dystrophic muscle changes. Use IV ...