A 3-year-old boy is brought to the office due to difficulty keeping up with the other children at day care. Over the last 2 months, the day care attendants have noticed that the patient has seemed more tired and less interested in active play. He has also had difficulty climbing stairs and jumping. The patient's parents mention that he is still eating well and gaining weight but has had recurrent upper respiratory infections since starting day care. His last upper respiratory infection began 5 days ago. Temperature is 37 C (98.6 F), blood pressure is 90/50 mm Hg, pulse is 94/min, and respirations are 18/min. Examination shows clear rhinorrhea bilaterally. Cardiopulmonary and abdominal examinations are normal. Neurologic examination demonstrates 1+ patellar and Achilles reflexes bilaterally. The calves are enlarged and nontender. Which of the following is the most likely cause of this patient's presentation?

Question

A 3-year-old boy is brought to the office due to difficulty keeping up with the other children at day care.  Over the last 2 months, the day care attendants have noticed that the patient has seemed more tired and less interested in active play.  He has also had difficulty climbing stairs and jumping.  The patient's parents mention that he is still eating well and gaining weight but has had recurrent upper respiratory infections since starting day care.  His last upper respiratory infection began 5 days ago.  Temperature is 37 C (98.6 F), blood pressure is 90/50 mm Hg, pulse is 94/min, and respirations are 18/min.  Examination shows clear rhinorrhea bilaterally.  Cardiopulmonary and abdominal examinations are normal.  Neurologic examination demonstrates 1+ patellar and Achilles reflexes bilaterally.  The calves are enlarged and nontender.  Which of the following is the most likely cause of this patient's presentation?

Quizplus · Accepted Answer

11ec25c8_d291_30c8_bc81_d52d5791caf5_MD0003_00 This patient has decreased endurance and calf pseudohypertrophy most likely due to Duchenne muscular dystrophy (DMD). DMD is an X-linked recessive disorder caused by markedly reduced or absent dystrophin, an integral protein found within the plasma membrane of primarily skeletal and cardiac muscle fibers. Without dystrophin, the muscle fibers are susceptible to degradation, resulting in muscle weakness. Typical presentation is a boy age <5 with difficulty walking, jumping, and climbing stairs due to proximal muscle weakness. Patients have trouble keeping up with other children and have decreased endurance (as in this patient). To compensate for the weakness, patients will frequently use their hands to "walk up" their legs in order to stand (Gower sign). Gower sign Calf pseudohypertrophy, in which the calf is enlarged due to muscle replacement by fat, is characteristic of DMD, and diminished reflexes can occur with loss of strength and tone. Over time, contractures develop in the Achilles tendons, causing patients to toe-walk, and most patients are wheelchair-dependent by adolescence. Diagnosis is confirmed by genetic testing. Glucocorticoids help improve function and delay disease progression. Most patients die by age 30 due to respiratory insufficiency or cardiac complications (eg, cardiomyopathy, arrhythmia). (Choice B) Myasthenia gravis is caused by antibodies to the acetylcholine receptor on the postsynaptic membrane. Patients most commonly have fluctuating weakness and fatiguability of the ocular muscles. The disease is rare in children, and isolated proximal lower extremity weakness is atypical. (Choice C) Viral myositis (ie, viral inflammation of muscle fibers) typically presents with acute muscle pain and weakness in the setting of a viral illness. This patient's prolonged symptoms and lack of muscle tenderness make viral myositis unlikely. (Choice D) Botulism, due to neurotransmitter neurotoxin blockade, causes symmetric descending weakness from the cranial nerves to the trunk and upper extremities. In contrast, this patient has lower extremity weakness. (Choice E) Guillain-Barré syndrome (GBS) is due to cross-reactivity of antibodies against an infection with peripheral nerve axons. Patients have ascending weakness and diminished reflexes. Although this patient has had recent upper respiratory infections, which are common in early childhood, progression of GBS typically occurs quickly over a couple of weeks, not months. Calf pseudohypertrophy would not be expected. Educational objective: Duchenne muscular dystrophy should be suspected in a boy age <5 with proximal muscle weakness and calf pseudohypertrophy. Patients have markedly reduced or absent dystrophin protein expression within the muscle. References: Duchenne muscular dystrophy: from diagnosis to therapy. (http://www.ncbi.nlm.nih.gov/pubmed/26457695)

A 3-Year-Old Boy Is Brought to the Office Due to Difficulty