Myopathy with muscle spindle excess: A new congenital neuromuscular syndrome?

An infant presented with congenital weakness, hypotonia, arthrogryposis, atrial tachycardia, and a left intra-abdominal neuroblastoma. Muscle biopsy revealed marked excess of muscle spindles with atrophy of extrafusal fibers. The patient expired at age 14 months from progressive cardiorespiratory failure. Postmortem examination demonstrated muscle-spindle excess in other muscles, along with hypertrophic obstructive cardiomyopathy and organomegaly. Muscle spindle excess has previously been reported in two patients with Noonan syndrome and progressive hypertrophic cardiomyopathy. Muscle spindle excess with hypertrophic cardiomyopathy, organomegaly, and, possibly, congenital neuroblastoma suggests a syndromic association and may represent an unusual form of congenital myopathy.