Congenital Myotonic Dystrophy
Neonates with congenital myotonic dystrophy have marked body and facial hypotonia. They usually do not appear alert. Arthrogryposis tends to be more common in the lower extremities than in the upper extremities (Figure 165.1). The distal joints are more involved than the proximal joints. The only distinguishing facial feature is temporal muscle atrophy, but this feature is seldom present at birth. The head is usually large. Magnetic resonance imaging of the brain may show ventricular dilation. The prognosis is poor. Mental retardation is usually noted as the patients get older. Congenital myotonic dystrophy is diagnosed by demonstrating the presence of myotonia in the mother and is confirmed by DNA testing. The disorder is caused by expansion in the number of trinucleotide repeats at chromosome region 19q13.3. It is an autosomal dominant disorder but the neonatal form only occurs if the mother is the affected parent. More about... 142

Figure 165.1.— Distal arthrogryposis in a neonate with congenital myotonic dystrophy.