Myotonic dystrophy: Aspiration risk

Myotonic dystrophy (MD) is a muscular disorder characterized by prolonged contraction and delay of relaxation of muscles, progressive muscle weakness, and wasting.Incidence is 1 in 8000

Signs and symptoms of MD1 includemuscle weaknessandwasting(especially in the cranial and distal limb musculature), myopathy, periodic myotonia,cardiac conduction abnormalities, insulin resistance, neuropsychiatric impairment, and cataracts (as well as testicular atrophy and frontal balding in men). Vocal cord apparatus may be affected. Mitral valve prolapse in 20%. First-degree AV block is common. MD2 also leads to myotonia and muscle dysfunction, but cardiac conduction defects are less common. May also lead to cataracts and NIDDM

Most anesthesia complications are pulmonary related. These patients are hypotonic, chronically aspirate, and hyperventilate.Gastric motility and cough reflexes are poor. SCh may produce contractions lasting for minutes. Etomidate, propofol, and neostigmine may induce myotonic reactions.Use short onset agents(ex. rocuronium) and avoid triggering factors such as hypothermia, shivering, and excess stimulation. These patients may be sensitive to anesthetic agents (hypersomnolence and CO₂ retention)

Myotonic reactions can be treated withphenytoinorquinine. Use short-acting agents when possible and monitor the cardiovascular system closely

According to Miller, “Patients with myotonia may be at increased risk for MH, although this is controversial“. According to MHAUS, “There are no case reports in the literature directly linking the myotonic dystrophies to MH. The IVCT of 44 patients with myotonias, including the myotonic dystrophies, resulted in 4 positive results, 10 equivocal results and 30 negative results [21]. The four positive results all came from DM patients, but 12 of these patients were negative. There is one report of a patient with DM2 who developed muscle stiffness, oculogyric cramps, and elevated creatine kinase levels after treatment with neuroleptics, and had a postivie IVCT with halothane [22]. Undoubtedly, the IVCT cannot be used to diagnose MH susceptibility in a patient population with membrane channelopathies without worrying about false positives [23]. Succinylcholine will induce generalized skeletal muscle rigidity in these patients, raising the specter of MH susceptibility, but the latter is unlikely to occur in the absence of a second genetic change specifically causative for MH“

Myotonic Dystrophy

• Background: 1:8000 incidence, prolonged contraction and delay of relaxation of muscles
• Manifestations: weakness; wasting;aspiration; conduction abnormalities; mitral valve prolapse; respiratory failure
• Triggers:hypothermia, shivering, excessive stimulation
• Management:avoid SCh(several minutes of tonicity), use short-acting agents when possible. Treat with phenytoin or quinine.MH risk unknown