What Are the Important Diagnoses to Consider?

Patients undergoing muscle biopsy present with a wide range of symptoms and no definitive diagnosis. Shapiro et al. has described a classification system for these patients based on presumptive preoperative diagnosis: myopathy or muscular dystrophy (MD), neuropathy or neuronal degeneration, metabolic or mitochondrial myopathy, seizures, cardiomyopathy, dermatomyositis. Patients with suspected diagnosis categories of myopathy or muscular dystrophy as well as metabolic or mitochondrial myopathy often have diseases that will alter anesthetic management. Special consideration to management of patients in these subsets is warranted.

How Is the Diagnosis of Muscular Dystrophy Made?

Muscle biopsy is the gold standard for diagnosis of many muscular disorders. The muscle to be biopsied is chosen based on the distribution of muscle weakness on physical exam. If weakness is generalized, often the quadriceps, specifically vastus lateralis, is chosen.

What Historical and Clinical Exam Findings Are Consistent with Muscular Dystrophy?

Muscular dystrophies are quite a heterogeneous group of disorders; however, most children present under the age of 4 years for muscle biopsy. Children with more severe forms of muscular diseases will present earlier in life.

Muscular dystrophy is characterized by painless muscle degeneration and atrophy. Any exam findings of muscular tenderness make MD less likely. Assessment of muscle bulk may be of some utility as myotonias often present early in life with muscle hypertrophy while other muscular disorders present with muscle wasting and atrophy.

What Testing Is Prudent to Narrow the Differential Diagnosis and Optimize the Patient’s Medical Condition Preoperatively?

Discussion with the referring physician and surgeon may be exceedingly helpful to ascertain likely diagnostic possibilities for each patient.

Muscular disorders may be suggested based on elevations of creatine phosphokinase (CK), creatine kinase of muscle (ckMB), blood urea nitrogen (BUN), aldolase, pyruvate, and lactic acid. More recently, genetic studies have become available for many disorders. For selected patients, hematologic studies and electromyography (EMG) can be suggestive of several diagnoses.

Medical optimization prior to biopsy includes determination of cardiopulmonary involvement. Tests such as chest roentgenogram, electrocardiogram, or echocardiogram may be indicated based on history, physical exam findings, and known comorbid associations with the presumptive diagnosis.

Muscular disorders associated with cardiac disease are shown in Table 14.1.

Are Airway Abnormalities Associated with Neuromuscular Disease?

Structural airway abnormalities, while uncommon, do occur in muscular disease. Scoliosis with relative rigidity of the spinal column may pose positioning and airway management challenges. Chondrodysplastic myotonia (Schwartz–Jampel Syndrome) is associated with micrognathia. Functional airway abnormalities, however, are quite common and are discussed below.

Cough clearance may be impaired due to neuromuscular weakness. The five phases of cough include irritation, inspiratory phase, glottic closure, compressive phase, and expulsive phase. Each of these phases may be affected by neuromuscular disease. Diaphragmatic (or other inspiratory muscle weakness) may impair inspiratory phase. Alternatively, glottic closure is affected by bulbar involvement as seen in motor neuron disease such as Duchenne muscular dystrophy. Similar to inspiratory phase compromise, expiratory phase compromise is related to weakness of the expiratory muscles. While expiration is usually passive, during coughing, expiration is facilitated by the rectus abdominis, abdominal obliques, and internal intercostal muscles.

Mucociliary airway clearance may be impaired in patients with chronic aspiration. Chronic deposition of mucus in the tracheobronchial tree prohibits proper clearance of new secretions.

Obstructive sleep apnea occurs with disease progression due to pharyngeal muscle weakness. Sleep study results should be reviewed if available.