Pediatric neuromuscular disorders

Published on 07/02/2015 by admin

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Last modified 22/04/2025

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Pediatric neuromuscular disorders

Andrea P. Dutoit, MD and Randall P. Flick, MD, MPH

Neuromuscular disorders (NMDs) affect a diverse group of pediatric patients with muscular and neurologic disease of varying complexity and origin. Perioperative concerns and management differ greatly depending on the specific cause of the disorder and the patient’s signs and symptoms, making it very important to be familiar with the precise underlying pathophysiology of the NMDs. This information is not always known, making anesthetic management of patients with NMDs challenging.

NMDs are often associated with other congenital disorders; pediatric patients with NMDs often present for elective surgical procedures to correct various deformities or for diagnostic purposes. The major and most common anesthetic concerns when caring for pediatric patients with NMDs are listed in Box 208-1. Several types of NMDs are briefly considered here, along with their major perioperative concerns.

Box 208-1   Anesthetic Considerations for Children with Neuromuscular Disorders

MAC, Minimum alveolar concentration; MH, malignant hyperthermia; NMD, neuromuscular disorders.

Cerebral palsy

Cerebral palsy (CP) and static encephalopathy are terms used for a collective group of nonprogressive disorders of movement involving abnormal development or prenatal injury to the brain. Although genetic abnormalities, perinatal anoxia, infection, and trauma have been proposed as etiologic factors in CP, no single cause has been identified. CP has a prevalence of 2 to 4 in 1000 live births, and patients with CP will have a variety of presentations, from near normal functional status to complete incapacitation. Clinical manifestations include disorders of posture due to spasticity or hypotonia of lower extremity or upper extremity muscle groups and abnormal speech or vision. Gastroesophageal reflux, behavior problems, mental retardation, and epilepsy can occur in some children with CP.

Muscular dystrophy

The muscular dystrophies (MDs) are characterized by progressive degeneration of skeletal muscles without signs of denervation. Duchenne MD (DMD) is an X-linked recessive disorder present in about 1 in 3500 male births. Symptoms of DMD are more severe than those that are part of Becker MD, although both disorders result from abnormalities of the dystrophin protein. In patients with DMD, affected muscles increase in size (pseudohypertrophy) as as result of muscle replacement with fat and connective tissue. Muscle weakness may not become evident until the patient is 2 to 5 years of age, but the weakness is rapidly progressive such that children are often wheelchair bound by 8 to 10 years of age and die by age 25. When succinylcholine is used in patients with MD, hyperkalemia may occur, whether or not the MD is clinically apparent. Because the manifestations of MD do not necessarily occur until children are older, many anesthesia providers avoid the use of succinylcholine in all males under the age of 10 years unless its use is indicated in emergency situations.

The preanesthetic evaluation of patients with MD should include an assessment of preexisting associated problems, such as kyphoscoliosis, as well as a thorough review of the cardiac system, given the increased prevalence of cardiomyopathy and the risk during anesthesia of cardiac complications occurring, such as heart failure or arrhythmias due to fibrosis of the electrical conduction system of the heart. The anesthesia provider should consider the potential for the patient to have respiratory muscle weakness and need postoperative mechanical ventilation and to be at increased risk for experiencing aspiration due to decreased laryngeal reflexes and gastric atony. The use of an inhalation agent for either induction or maintenance of anesthesia is controversial because of the perceived increased risk of children with MD developing malignant hyperthermia (MH), although studies have shown no clear association (see discussion later).

Mitochondrial myopathies

Mitochondrial myopathies are a very rare complex group of disorders characterized by defects in the electron transport chain or oxidative phosphorylation of skeletal muscle. The manifestations include generalized muscle fatiguability, progressive weakness, hypoglycemia, metabolic and respiratory acidosis, and stroke. Affected organ systems include not only those with high O2 demands, such as the brain and heart, but also the liver and kidneys.

Surgical stress can decrease the O2 supply-demand ratio because of an increase in O2 demand, leading to hypoxia in the patient who is under anesthesia. Mitochondrial disorders have no direct link to MH but it has been suggested that the use of propofol in these patients may lead to a progressive metabolic acidosis similar to that seen in the propofol infusion syndrome.

Malignant hyperthermia and neuromuscular disorders

Despite continuing controversy, it is widely assumed that children with known or suspected myopathies are at increased risk for developing MH. Previous reports have suggested a relationship between MH risk and a variety of NMDs, including DMD, osteogenesis imperfecta, myotonia congenita, Schwartz-Jampel syndrome, Kearns-Sayre syndrome, and others. A clear link to MH has been established for only two disorders: central core disease and King syndrome. Both are quite rare, well-defined clinically, autosomal dominant, and frequently diagnosed without muscle biopsy.

Much of the difficulty associated with defining the relationship between MH and MD is related to the phenomenon of acute rhabdomyolysis. Acute rhabdomyolysis leading to hyperkalemic cardiac arrest has been reported to occur in association with MDs and with myopathies and has been understandably confused with MH. Presenting symptoms and signs of acute rhabdomyolysis are very similar to those of MH and include fever, hypercarbia, tachycardia, acidosis, hyperkalemia, arrhythmias, and elevated creatine kinase levels. If untreated, both rhabdomyolysis and MH may result in death. Similar to MH, most reported cases of rhabdomyolysis have been associated with the use of succinylcholine, although several cases have occurred in its absence. Inhalation anesthetic agents have subsequently been implicated as well, although the mechanism by which this occurs remains, to a large extent, unexplained. For these reasons, it is common to avoid the use of triggering anesthetic agents (succinylcholine and inhalation agents) in patients with MD.

The most commonly mentioned alternative to the use of inhalation anesthetics agent in this population is total intravenous anesthesia (e.g., propofol). Theoretically, the use of propofol in patients with MD is also controversial given the reports of rhabdomyolysis, unrelenting acidosis, and death that have occurred when propofol was used at high doses in children. It has been recommended that anesthesia providers who administer anesthesia to children who have or may have mitochondrial disorders consider avoiding the use of propofol due to concerns that this group may be at particular risk for developing the propofol infusion syndrome.

Because of the rarity of both MH and rhabdomyolysis, most studies are underpowered to be able to demonstrate the safety of using inhalation anesthetic agents in the setting of suspected myopathy. Studies that include small groups of patients have shown that, in a diverse population of children undergoing muscle biopsy for known or suspected myopathy, the incidence of MH or rhabdomyolysis is extremely uncommon even when succinylcholine or inhalation anesthetic agents have been used. The estimated risk of MH or rhabdomyolysis attributed to the use of these agents is probably less than 1.0%. Each anesthesia provider must decide, based on these results, whether the risk is sufficient to justify the use of an alternative anesthetic agent, such as propofol, or some other approach, such as the use of etomidate (adrenal suppression), dexmedetomidine (bradycardia and hypotension), ketamine (hallucinations), or a regional technique (acceptance/cooperation).

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