Myotonic dystrophy (dystrophia myotonica, DM) is a muscular disorder characterized by prolonged contraction and muscle relaxation, progressive muscle weakness, and wasting. Intraoperative management should aim to avoid triggering myotonia and should take into account that DM patients are at increased risk for the following:
- Cardiac conduction abnormalities
- Hypersensitivity to anesthetic agents
- Metabolic abnormalities, including hyperkalemia and hyperglycemia
Regional anesthesia has been successfully used as a primary anesthetic in DM patients and can help reduce the risk of the manifestations stated above. However, regional technique may place the patient at increased risk of myotonia secondary to shivering and/or insufficient motor block to blunt the response to surgical stimulation.
Specific intraoperative anesthetic considerations with regards to general anesthesia and DM are discussed below.
Monitoring – in addition to ASA standard monitors, one should consider an arterial line in order to quickly identify hemodynamic instability associated with cardiac conduction abnormalities and to facilitate serial monitoring of serum electrolytes. Pacing equipment should also be readily available, as there have been reports of third-degree atrioventricular block refractory to atropine. Other invasive monitors may be considered, taking into consideration the patient’s pre-operative cardiopulmonary status.
Induction – DM patients have weak pharyngeal musculature and are therefore at greater risk of aspiration. Ideally, a rapid sequence induction without neuromuscular blockade should be performed. Avoid succinylcholine; it may induce exaggerated contracture, masseter spasm, laryngospasm, or severe hyperkalemia. If neuromuscular relaxation is necessary, use shorter-acting agents, such as rocuronium or cis-atracurium.
Maintenance – intravenous or inhalational agents are appropriate; DM patients are no more susceptible to malignant hyperthermia than the general population. The patient will require deeper anesthesia for akinesia if neuromuscular relaxant is not used.
Emergence – avoid paralytic reversal; neostigmine may exacerbate myotonia. Prolonged emergence can be expected due to hypersensitivity to anesthetic agents. Strict extubation criteria should be employed, given the patient’s increased risk of aspiration.
Environment – hypothermia and shivering can induce myotonia. Thus, normothermia should be maintained with warm IV fluids and a forced warm air blanket if necessary.