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Literature Review

Myotonic dystrophy and paediatric anaesthesia.

RJ White and SP Bass. Paediatric Anaesthesia 2003;13:94-102.

Summary. The authors provide a comprehensive review of the perioperative management of patients with the congenital (neonatal) form of this disorder. With improvements in supportive care, many of these infants are making their way to the OR. Common procedures for this group of patients include tracheostomy, gastrostomy, fundoplication, abdominal wall hernia repair, BMT, and clubfoot release.

Myotonic dystrophy is an autosomal recessive inherited disorder located on chromosome 19. The affected gene has abnormal, repeated sequences of cytosine, thymine and guanine (CTG), where the size of the repeat is correlated with clinical severity. The gene is not linked to malignant hyperthermia susceptibility. Myotonic episodes are characterized by lack of normal muscle relaxation and are due to abnormal chloride conductance and sodium channel permeability in the muscle membrane.

Infants usually present with hypotonia, poor suck & swallow, poor weight gain, and developmental delay. Otitis media, GERD, abdominal wall hernias, and mild retardation (average IQ 66) are common. Other findings include facial diplegia with "tent-shaped" mouth, ptosis, and recurrent aspiration pneumonia. In the pre-operative history, it is important to identify triggers of myotonic episodes, and the frequency/duration of mechanical ventilation with respiratory infections. Drugs used to prevent myotonia include (fos)phenytoin, quinine and procainamide. Notably, phenytoin induces hepatic enzymes, decreases MAC, and antagonizes nondepolarizers (except atracurium). Procainamide increases the duration of muscle relaxants and antagonizes neostigmine.

Preoperatively, patients should have their nutritional and respiratory statuses optimized and a chest x-ray performed. Because cardiac conduction defects, mitral regurgitation and decreased LV function are common, electro- and echocardiograms are warranted.

Extreme caution should be taken with premedication due to the potential for respiratory depression. Aspiration precautions are prudent. When inducing anesthesia it is important to realize that many things can induce myotonic crises including application of a venous tourniquet, venipuncture, struggling to resist induction, succinylcholine, the pain of propofol injection, surgical manipulation, hypothermia, nerve stimulation, and electrocautery. Despite full neuromuscular blockade, myotonia may still occur. All anesthetic drugs have potentially deleterious effects on cardiorespiratory function and must be used cautiously. Dose requirements for propofol may be increased or decreased.

Epidural, caudal, and spinal anesthesia have all been used successfully in these patients. For postoperative pain control, NSAIDS and infiltration of the incision with local anesthetics are attractive choices.

Comment. Pediatricians are taught to suspect the diagnosis when shaking one's hand and finding they cannot release their grip. The authors discuss the possibility of mask induction and use of a LMA. These options would likely be less well received in the USA. Careful titration of drugs, use of atracurium if paralysis is needed, and avoidance of succinylcholine are essential. The need to maintain postop ventilation should be based on preop history, surgical procedure, and respiratory effort on emergence.

Reviewed by: Samuel Golden, MD, FAAP

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