A 9-year-old boy is brought to the clinic due to poor academic performance. The patient receives special needs education, including speech therapy. His teachers have had difficulty keeping his attention in class, and his grades are declining. Over the last few weeks, the patient has been falling asleep at his desk. He watches television in the evenings until bedtime at 9 PM and wakes at 7 AM every day. He feels tired most days and is occasionally sad because his parents recently divorced. Blood pressure is 104/70 mm Hg and respirations are 26/min. Weight and height are at the 50th and 20th percentile, respectively. Tonsils are 1+. Cardiopulmonary examination is normal. The patient has difficulty opening his hands after squeezing the examiner's fingers. There is full range of motion in the bilateral extremities. Which of the following is the most likely explanation for this patient's clinical presentation?

Question

A 9-year-old boy is brought to the clinic due to poor academic performance.  The patient receives special needs education, including speech therapy.  His teachers have had difficulty keeping his attention in class, and his grades are declining.  Over the last few weeks, the patient has been falling asleep at his desk.  He watches television in the evenings until bedtime at 9 PM and wakes at 7 AM every day.  He feels tired most days and is occasionally sad because his parents recently divorced.  Blood pressure is 104/70 mm Hg and respirations are 26/min.  Weight and height are at the 50th and 20th percentile, respectively.  Tonsils are 1+.  Cardiopulmonary examination is normal.  The patient has difficulty opening his hands after squeezing the examiner's fingers.  There is full range of motion in the bilateral extremities.  Which of the following is the most likely explanation for this patient's clinical presentation?

Quizplus · Accepted Answer

11ec25c8_d6f8_81e3_bc81_2b3a408eebd9_MD0003_00 Myotonic dystrophy is a multisystem genetic disorder caused by a trinucleotide (CTG) repeat expansion in the dystrophia myotonica protein kinase (DMPK) gene. The classic form presents in adolescence or adulthood, but an earlier onset in infancy and childhood, as seen here, occurs with longer CTG repeats. The childhood phenotype of myotonic dystrophy presents by age 10, often with predominantly cognitive (eg, intellectual impairment) and behavioral manifestations (eg, attention deficit hyperactivity disorder, mood disorder), such as in this child with poor academic performance. Sleep disturbances, including excessive daytime sleepiness, are also common but often go unrecognized. The hallmarks of the disease are muscle weakness and myotonia (delayed muscle relaxation). Grip myotonia, as seen in this patient, is characterized by difficulty opening the hand after squeezing it closed and is highly suggestive of myotonic dystrophy. Weakness of the facial (eg, ptosis) and distal (eg, footdrop, poor finger dexterity) muscles develops over time. Dysphagia and arrythmias can also occur due to smooth and cardiac muscle involvement, respectively. Genetic testing confirms the diagnosis, and treatment is supportive. Respiratory muscle failure and cardiac arrhythmias are responsible for most deaths (average age 45-55). (Choice A) Absence seizures can present with declining academic performance due to perceived inattention during the ictal period. However, excessive sleepiness and myotonia make this diagnosis unlikely. (Choice B) Fatigue, poor academic performance, and sadness following his parents' divorce may support a diagnosis of adjustment disorder in this patient. However, myotonia is not associated with adjustment disorder. (Choice C) Patients with cerebral palsy typically have nonprogressive motor impairment and/or intellectual disability and behavioral problems. However, the motor dysfunction in cerebral palsy is usually characterized by hypertonicity and hyperreflexia, not myotonia. (Choice E) Narcolepsy causes excessive daytime sleepiness, which may present with poor academic performance. However, narcolepsy is associated with cataplexy (sudden loss of tone), not myotonia. (Choice F) Poor sleep hygiene includes excessive screen time before bed, which can contribute to a prolonged sleep-onset latency. However, this patient is maintaining an age-appropriate amount of sleep (10 hours), which does not account for his excessive daytime sleepiness. In addition, poor sleep hygiene would not cause myotonia. Educational objective: Myotonic dystrophy is a multisystem genetic disorder with variable severity and phenotype that classically causes muscle weakness and myotonia. Sleep disturbances, including excessive daytime sleepiness, are a common, yet often underrecognized, feature. The childhood phenotype (age of onset <10) often presents with intellectual impairment and behavioral issues. References: Congenital and childhood myotonic dystrophy: current aspects of disease and future directions. (http://www.ncbi.nlm.nih.gov/pubmed/26566479)

A 9-Year-Old Boy Is Brought to the Clinic Due to Poor