A 9-year-old boy is brought to the physician for a well-child examination. His mother says his teachers report him being easily distracted, lagging behind his classmates in most of the subjects, and frequently falling asleep during class. She says that her son has complained of leg pain on multiple occasions. He is at the 45th percentile for height and 35th percentile for weight. Vital signs are within normal limits. Examination shows ptosis and a high-arched palate. Muscle strength is decreased in the face and hands. Muscle strength of the quadriceps and hamstrings is normal. Sensation is intact. Percussion of the thenar eminence causes the thumb to abduct and then relax slowly. The patient's condition is best described as which of the following?

Question

Quizplus · Accepted Answer

Eductional Objective: Myotonic dystrophy is an autosomal-dominant disorder.  It is caused by an increased number of trinucleotide repeats on myotonia-protein kinase gene.  Sustained muscle contraction (myotonia), along with weakness and atrophy, is common.  Cataracts are seen in almost all patients.  Frontal balding and gonadal atrophy are other common features.

A 9-Year-Old Boy Is Brought to the Physician for a Well-Child