Becker’s muscular dystrophy: Rhabdomy

Muscular dystrophy is a group of hereditary diseases characterized by painless degeneration and atrophy of skeletal muscles. There is symmetric skeletal muscle weakness/wasting without denervation (sensation and reflexes are intact). X-linked recessive types (Duchenne and Becker muscular dystrophies) are the most prevalent types of muscular dystrophy. Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) are caused by a recessive mutation on the X-chromosome that prevents normal formation of dystrophin, a muscle stabilizing protein. Complete loss of dystrophin (as in DMD) or a partially functional dystrophin protein (as in BMD) disrupts sarcolemma integrity leading to myofibril atrophy, necrosis, and fibrosis. BMD progresses at a slower rate than DMD with most BMD patients presenting with weakness in adolescence and most DMD patients presenting with weakness and motor delay in childhood (often delayed walking).

Patients with DMD and BMD may have life-threatening perioperative complications related to triggering agents that induce skeletal muscle breakdown (rhabdomyolysis) with resultant hyperkalemia. Succinylcholine administration in patients with DMD and BMD is associated with life-threatening rhabdomyolysis and hyperkalemia (1). There are two general mechanisms underlying succinylcholine-induced hyperkalemia: excess potassium release as a result of upregulation of abnormal extrajunctional acetylcholine receptors (i.e. burns, denervation, atrophy) and development of hyperkalemia as a result of rhabdomyolysis that occurs in patients with myopathic disease states, such as DMD and BMD. Of note, patients with DMD and BMD may not have upregulation of abnormal extrajunctional acetylcholine receptors.

In a large literature review of anesthetic complications involving patients with muscular dystrophy, Gurnaney et al. (2009) identified three patients with BMD who received a volatile anesthetic without succinylcholine and developed anesthesia-related cardiac arrest (one intraoperatively, two in the recovery room). All patients received dantrolene to treat presumed MH; however, a diagnosis of MH was thought to be unlikely in the absence of a hypermetabolic state preceding the rhabdomyolysis and hyperkalemic event (that led to cardiac arrest). The pathophysiology of inhaled anesthetic-induced rhabdomyolysis in patients with DMD and BMD is unknown; it has been hypothesized that inhaled anesthetics exacerbate a breakdown of the muscle membranes in these patients. Of note, the notion of volatile anesthetic-induced rhabdomyolysis in patients with muscular dystrophy has been questioned (2) despite recommendations from the American College of Chest Physicians and the American Academy of Pediatrics to avoid volatile anesthetics in these patients (3,4).

Some sources report an increased incidence of malignant hyperthermia in patients with muscular dystrophy, including a review of pediatric patients reported to the Malignant Hyperthermia Registry as suffering cardiac arrest within 24 hours of anesthesia (8 of 25 patients were found to have DMD) (5,6). However, Gurnaney et al. (2009) did not find an increased risk of malignant hyperthermia susceptibility in patients with DMD or BMD compared with the general population; they did note that patients with muscular dystrophy who are exposed to inhaled anesthetics may develop disease-related cardiac complications, or rarely, a malignant hyperthermia-like syndrome characterized by rhabdomyolysis (without evidence of hypermetabolism). Furthermore, DMD and BMD have different genetic backgrounds than MH, which is associated with chromosome 191.