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Difficulty: MediumPediatric Neurologic Disorders

A 4-year-old boy is brought to the pediatric clinic by his parents due to concerns about his frequent falls and difficulty climbing stairs. The parents report that he tires more easily than his peers when playing at the local park. When getting up from a sitting position on the floor, he uses his hands to push himself up his thighs to stand upright. His developmental history is significant for walking independently at 16 months, and he currently speaks in short sentences. His temperature is 37.0°C (98.6°F), pulse is 95/min, respirations are 20/min, and blood pressure is 95/60 mm Hg. Physical examination reveals bilaterally enlarged, firm calf muscles and a waddling gait. Which of the following is the most appropriate next step in evaluation?

  1. Serum creatine kinase levelAnswer
  2. B
    Reassurance and routine follow-up
  3. C
    Echocardiography
  4. D
    Intravenous ceftriaxone and vancomycin
  5. E
    Deferral of scheduled live-attenuated vaccines

Answer

Serum creatine kinase level
The patient presents with frequent falls, a waddling gait, and the use of his hands to push himself up from the floor (Gowers sign). These findings indicate proximal muscle weakness. Combined with bilaterally enlarged, firm calf muscles (pseudohypertrophy), the clinical picture is highly suspicious for Duchenne muscular dystrophy (DMD). DMD is an X-linked recessive disorder caused by a frameshift mutation in the dystrophin gene. The absence of dystrophin leads to muscle fiber fragility and necrosis. Because muscle damage occurs early and continuously, the most appropriate initial screening test is a serum creatine kinase (CK) level, which is typically markedly elevated (often 10 to 20 times the upper limit of normal). If the CK level is elevated, the diagnosis is subsequently confirmed with genetic testing.

Step-by-Step Solution

1
Analyze the patient's motor symptoms and physical examination findings.
The 4-year-old boy demonstrates proximal muscle weakness (Gowers sign) and bilaterally enlarged, firm calf muscles (pseudohypertrophy).
Recognizing the constellation of Gowers sign and calf pseudohypertrophy in a young male points to a progressive neuromuscular disease, specifically Duchenne muscular dystrophy (DMD).
2
Determine the most appropriate initial diagnostic approach for the suspected condition.
Obtain a serum creatine kinase (CK) level.
Because DMD is caused by an absence of the dystrophin protein, the muscle membrane becomes fragile, leading to muscle breakdown. This results in a massive release of CK into the blood, making it the most sensitive initial screening test before definitive genetic testing.

Key Concept

Diagnosis of Duchenne Muscular Dystrophy
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Topics

Pediatric Neurologic Disorders

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