Muscular+Dystrophy

Muscular Dystrophies encompass a diverse group of disorders with varying modes of inheritance and pathophysiological charecteristics. The most prevalent are the X linked recessive types, DMD and BD. Numerous publications have suggested an assoc. between these 2 MD and increased risk of MH episode.
 * //Duchenne Muscular Dystrophy //**
 * DMD **
 * Occurs ** app. 30 per 100000 liveborn males.
 * Caused **by a recessive mutation on the X-chromosome that prevents normal formation of dystrophin, a muscle-stabilizing protein. Dystrophin is an important part of the dystrophin-glycoprotein complex. The dystrophin-glycoprotein complex is part of a larger complex of proteins associated with dystrophin, which plays a role in sarcolemmal integrity. Loss of dystrophin (partial in BD or complete in DMD) disrupts sarcolemmal integrity and leads to muscular dystrophy.


 * Presents **
 * in early childhood as weakness and motor delay.
 * Delayed walking beyond 15-mo-old is a common initial sign.
 * During development, clinical manifestations include progressive lower extremity weakness, pseudohypertrophy of the calves, and markedly elevated creatine kinase levels.
 * Almost all patients with DMD are symptomatic by the age of 5 yr, with difficulty running, jumping, climbing steps, and a waddling gait.
 * Proximal weakness causes patients to use their arms in rising from the floor (Gower’s sign).
 * Progressive and severe muscle atrophy and weakness cause loss of the ability to ambulate by the age of 14 yr.
 * <span style="font-family: 'Palatino-Roman','serif';">Cardiac disease DMD manifests as a dilated cardiomyopathy and/or cardiac arrhythmias. Approximately, one third of the patients with DMD develop cardiomyopathy by the age of 14 yr and almost all patients have cardiomyopathy by the age of 18 yr.
 * <span style="font-family: 'Palatino-Roman','serif';">Patients with DMD ultimately die in early to midadulthood secondary to a progressive cardiomyopathy and/or ventilatory pump insufficiency <span style="font-family: 'Palatino-Roman','serif'; font-size: 13.3333px;">.


 * <span style="font-family: 'Palatino-Roman','serif'; font-size: 18.6667px;">The risks **<span style="font-family: 'Palatino-Roman','serif';"> related to anesthesia and sedation for patients with DMD include potentially fatal reactions to certain anesthetics, upper airway obstruction, hypoventilation, atelectasis, congestive heart failure, cardiac dysrhythmias, respiratory failure, and difficulty weaning from mechanical ventilation.


 * <span style="font-family: 'Palatino-Roman','serif'; font-size: 18.6667px;">Preoperative evaluation **<span style="font-family: 'Palatino-Roman','serif';"> in patients with DMD should include
 * <span style="font-family: 'Palatino-Roman','serif';">A detailed work-up of their pulmonary function, which includes measurement of forced vital capacity, maximum inspiratory pressure, maximum expiratory pressure, and peak cough flow.
 * <span style="font-family: 'Palatino-Roman','serif';">Preoperative training with assist devices should be considered based on their pulmonary function.
 * <span style="font-family: 'Palatino-Roman','serif';">Complete cardiac evaluation should be undertaken before any surgical procedure and a dobutamine stress test should be considered if any abnormalities of cardiac function are present. Medical therapy of any cardiac dysfunction should be optimized before any surgery.


 * <span style="font-family: 'Palatino-Roman','serif'; font-size: 18.6667px;">Four categories of anesthetic complications **<span style="font-family: 'Palatino-Roman','serif';"> have been identified in patients with DMD :
 * <span style="font-family: 'Palatino-Roman','serif';">disease-related (DMD) intraoperative heart failure
 * <span style="font-family: 'Palatino-Roman','serif';">rhabdomyolysis and hyperkalemic cardiac arrest in the absence of succinylcholine administration,
 * <span style="font-family: 'Palatino-Roman','serif';">acute hyperkalemia after administration of succinylcholine
 * <span style="font-family: 'Palatino-Roman','serif';">MH.


 * <span style="font-family: 'Palatino Linotype','serif'; font-size: 18.6667px;">Do Muscular Dystrophy Patients have an Increased Risk of MHS? **
 * <span style="font-family: 'Palatino-Roman','serif';">The rhabdomyolysis and other clinical characteristics that result from administration of succinylcholine and volatile anesthetics to patients with DMD share signs similar to those arising from a true MH episode; thus, the two entities are difficult to distinguish.
 * <span style="font-family: 'Palatino-Roman','serif';">The clinical presentation of an episode of MH can be variable and some patients may not demonstrate significant rhabdomyolysis or even lactic acidosis.
 * <span style="font-family: 'Palatino-Roman','serif';">It seems unlikely that there is a true genetic association between DMD and MH because the genetic mutation associated with DMD is located on the X chromosome, and the mutations associated with MHS are usually found on chromosome 19.
 * <span style="font-family: 'Palatino-Roman','serif';"> Nevertheless, some patients with DMD have demonstrated a positive caffeine-halothane contracture test indicating MHS. The validity of a caffeine halothane contracture test in patients who have muscular dystrophy has been debatable as the muscles in these patients may be prone to a positive test on exposure to triggering agents.
 * <span style="font-family: 'Palatino-Roman','serif';">However, in all the “clinical MH” cases, the patients suffered acute rhabdomyolysis with hyperkalemia without other classic signs and symptoms of MH, and did not have any evidence of hypermetabolism, which is a hallmark of MH.


 * <span style="font-family: 'Palatino-Roman','serif'; font-size: 18.6667px;">Anesthetic Considerations **<span style="font-family: 'Palatino-Roman','serif';">:
 * <span style="font-family: 'Palatino-Roman','serif';">Although muscular dystrophy patients are unlikely to have an increased risk of MHS, exposure to **<span style="font-family: 'Palatino-Roman','serif'; font-size: 18.6667px;">volatile anesthetics **<span style="font-family: 'Palatino-Roman','serif';"> may be associated with life-threatening rhabdomyolysis and therefore should be used cautiously and when the benefits of their use outweigh the possible risks.
 * **<span style="font-family: 'Palatino-Roman','serif'; font-size: 18.6667px;">Succinylcholine **<span style="font-family: 'Palatino-Roman','serif';"> administration is associated with life threatening hyperkalemia and should be avoided in patients with DMD unless required as a last resort for a life-threatening airway emergency.
 * <span style="font-family: 'Palatino-Roman','serif';">Undiagnosed motor delay or loss of motor milestones should prompt neurological evaluation before administration of general anesthetics.