A severe congenital form of DM can appear in infants of mothers with myotonic dystrophy because of rapid expansion of the CTG repeat length. Infants are immobile and hypotonic, with ptosis, absence of sucking and Moro reflexes, poor feeding, and respiratory difficulties. Often, weakness and atony of uterine smooth muscle during labor lead to associated hypoxic ischemic encephalopathy and its sequelae, which make the clinical diagnosis more difficult. The presence of congenital contractures, clubfoot, or a history of poor fetal movements indicates intrauterine neuromuscular disease. Those requiring prolonged ventilation have an infant mortality of 25%. Individuals with congenital DM often make significant gains in terms of motor skills, and nearly all children eventually ambulate independently. However, approximately 50% of DM patients have mental retardation. In addition, children with congenital DM experience a second progressive phase of the disease in the teen years, including potentially fatal cardiac arrhythmias.
Diagnosis is established by genetic testing.
Other Forms of Childhood Muscle Disease
Congenital muscular dystrophies (CMDs) refer to a group of genetically determined conditions that present in infancy or early childhood. The most common subtypes include merosin-deficient congenital muscular dystrophy, Ullrich congenital muscular dystrophy, and the dystroglycanopathies. The characteristic clinical features include hypotonia, extremity weakness, delayed motor development, and congenital contractures. Diagnosis is established through the combination of elevated serum CK and dystrophic changes detected on muscle biopsy. In most individuals, the disease course is slow or nonprogressive, although many children with CMD are wheelchair dependent and require some type of respiratory support. Contractures and scoliosis are often progressive and severely worsen; respiratory status diminishes with age.
Emery-Dreifuss muscular dystrophy (EDMD), also known as humeroperoneal muscular dystrophy, can be inherited as an X-linked recessive, autosomal dominant, or autosomal recessive disorder. Symptoms typically begin in childhood, although adult onset has been noted. Patients may experience early contractures, slowly progressive humeroperoneal muscle weakness or wasting, and cardiac disease with conduction defects and arrhythmias. EDMD is associated with mild elevations of serum CK levels, abnormal electrocardiograms (ECG), characteristic changes on muscle imaging, and abnormal but nonspecific muscle biopsies. There are no disease-specific modifying therapies for EDMD, although early placement of defibrillators in patients with abnormal ECGs reduces the incidence of sudden death.
Several forms of limb-girdle muscular dystrophy (LGMD) have been described, which are usually inherited in an autosomal recessive pattern. Depending on the subtype of LGMD, presentation can be throughout childhood. A subset of children will have a Duchenne-like presentation. LGMD primarily affects muscles of the hip and shoulder girdles. Distal muscles may later become weak and atrophic. Many children with LGMD will lose the ability to ambulate. Some may also have progressive cardiac and respiratory failure.
Facioscapulohumeral dystrophy is an autosomal dominant myopathy. Weakness first appears in the facial and shouldergirdle muscles. Shoulder weakness results in the characteristicobservation of scapular winging, which can often be asymmetric. Patients have mild ptosis, a decrease in facial expression,inability to pucker the lips or close eyes during sleep, neckweakness, difficulty in fully elevating the arms, and thinness ofupper arm musculature. Progression is slow, although childrenoften have a more severe presentation and can have significantdisability related to upper extremity weakness and dysfunction.