Respiratory Disorders Associated With Neuromuscular Disease

Laura Beth Mann Dosier, MD, and Richard M. Kravitz, MD, FAAP

Introduction/Etiology/Epidemiology

•Neuromuscular disease is not 1 specific entity but represents a variety of diseases where an abnormality develops anywhere between the peripheral nervous system and the muscle, resulting in muscle weakness.

•The point of origin of this defect can be

—Lower motor neuron

—Peripheral nerves

—Neuromuscular junction

—Muscle

•Various etiologic origins of this class of diseases include

—Inherited

—Autoimmune

—Infectious

•Examples of the more commonly seen diseases include

—Spinal muscular atrophy (types 1, 2, 3)

—Charcot-Marie-Tooth disease

—Guillain-Barré syndrome

—Becker muscular dystrophy

—Duchenne muscular dystrophy

—Facioscapulohumeral muscular dystrophy

—Limb girdle muscular dystrophy

—Emery-Dreifuss muscular dystrophy

Pathophysiology

•Muscle tone abnormalities can lead to

—Ineffective or diminished cough

▪Impaired airway clearance

—Altered upper-airway tone with subsequent collapse and obstruction

▪Obstructive sleep apnea

▪Respiratory failure

—Altered swallowing function (especially if bulbar dysfunction is present)

▪Inability to handle oral secretions

▪Higher risk for aspiration of secretions and food

▪Weight loss exacerbating further muscle weakness

•Scoliosis is the chief orthopedic complication and can lead to

—Development of restrictive lung disease

—Altered airway clearance

—Abnormal insertion of the esophagus through the diaphragm and loss of lower esophageal sphincter tone, leading to gastroesophageal reflux (GER)

•Gastrointestinal complications include

—Increased GER

—Secondary aspiration

—Constipation

Clinical Features

•Different neuromuscular diseases have various modes of presentation.

—Duchenne muscular dystrophy

▪Symptoms are often evident by 4 years of age.

▪Duchenne muscular dystrophy usually manifests with tripping, falling, or difficulty standing up without assistance (pushing up on the legs to reach a standing position [Gower maneuver]).

—Spinal muscular atrophy (SMA)

▪Type 1: Early hypotonia (<6 months old) and patient cannot sit independently

▪Type 2: Patient never able to walk but can sit independently (6–24 months old)

▪Type 3: Patient able to walk but may have gradually increasing weakness (>18 months old)

▪Type 4: Onset in adulthood

•Respiratory symptoms of neuromuscular disease include

—Decreased exercise tolerance

—Cough that is weak, chronic, or recurrent in quality

—Chronic throat clearing

—Recurrent lower respiratory tract infections

—Progressive dyspnea

—Sleep-related issues

▪Snoring

▪Apneas

▪Morning headaches

▪Daytime sleepiness

—Feeding issues

▪Choking, gagging, and/or coughing with eating

—Weak cough

—Snoring

—Scoliosis

—Gower maneuver (pushing up on the legs to reach a standing position)

—Pseudohypertrophy of the calf muscles (in Duchenne muscular dystrophy)

—Tongue fasciculations (in SMA)

Differential Diagnosis

•The differential diagnosis for respiratory distress (shortness of breath, tachypnea, retractions, hypoxia) in children with neuromuscular disease includes

—Atelectasis secondary to

▪Weak cough and suboptimal secretion clearance

▪Recurrent infections

▪Hypoventilation with low lung volumes

▪Chronic microaspiration

—Pneumonia

—Aspiration

—Restrictive lung disease secondary to

▪Muscle weakness

▪Scoliosis

—Progressive respiratory failure

—Heart failure (cardiomyopathy is seen in several muscular dystrophies)

Diagnostic Considerations

•Muscular dystrophy is diagnosed by means of

—Creatine kinase level