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Anesthetic Management in a Parturient with Myotonia Congenita
Abstract Number: T1D-2
Abstract Type: Case Report/Case Series
Intro: Patients with neuromuscular disorders are of interest to the anesthesiologist. We present a patient with myotonia congenita (MC) scheduled for repeat cesarean section.
Case: The patient is a 35 y.o. G2P1 at 39 weeks gestation who was diagnosed with Thomsen’s Disease, the autosomal dominant form of MC, after noting muscle rigidity in her first pregnancy. The patient reported a need to “warm up” after inactivity and difficulty turning her neck; but denied weakness. Physical exam revealed normal sensation and motor function with myotonia after deep tendon reflexes. Her airway exam was reassuring except for limited neck range of motion and over developed neck muscles. After difficulty with ambulation to the OR, surgical anesthesia was induced with 12 mg hyperbaric bupivacaine, 15 mcg fentanyl, and 100 mcg preservative-free morphine via combined spinal-epidural (CSE) at L3/4 in the sitting position. An infusion of phenylephrine was initiated with co-administration of lactated ringers. While lying supine, she developed lower extremity rigidity inhibiting foley catheter placement for several minutes. Delivery of a live born infant with APGARS 9 and 9 was completed otherwise uneventfully with no evidence of hemodynamic instability, shivering, hypothermia, or discomfort.
Discussion: MC is caused by CLCN1 gene mutations that express chloride channel defects in the sarcolemma and lead to skeletal muscle excitability and myotonia with an incidence of 1:100,000. Triggers such as physical activity (shivering and labor), emotional stress (pain), environmental factors (extremes of temperature), and electrolyte abnormalities may worsen symptoms. Our management focused on minimizing hemodynamic disturbances and limiting stressful triggers. Midazolam was declined by the patient. A CSE was chosen for the ability to prolong blockade, avoid general anesthesia in this patient with potential for difficult airway, and to avoid precipitating medications. Depolarizing muscle relaxants should be avoided due to reports of severe, generalized muscle stiffness and hyperkalemia. In contrast, responses to non depolarizing neuromuscular blockers (NMBDs) are normal in Thomsen’s Disease which is not associated with muscle wasting. However, acetylcholinesterase inhibitors are known triggers. The availability of sugammadex may be of benefit in this patient population. In the event of rigidity, NMBDs are ineffective as the defect is distal to their site of action. Epinephrine, beta-adrenergic agonists, and beta blockers may provoke rigidity as well. Although previously thought to be associated with malignant hyperthermia (MH), myotonia congenita is no longer considered a risk factor for MH.
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4.Conravey et al. Curr Treat Options Neurol 2010;12:16–28