A 3-year-old boy is brought to the office by his parents due to leg pain. Over the past 3 months, he has had progressive, bilateral lower leg pain that is worse with activity. The patient began walking at age 19 months and has always walked on his toes. He has had no fever, joint swelling, or rash. The patient takes no medications, and his immunizations are up to date. He was adopted as an infant, and his biological family history is unknown. Examination shows bilateral calf enlargement and thin, atrophied thighs. There is no focal tenderness with palpation. The patient has a waddling gait. His creatine kinase level is markedly elevated. Muscle biopsy shows replacement of muscle by fat and connective tissue. Which of the following additional tests should be performed at this time?

Question

A 3-year-old boy is brought to the office by his parents due to leg pain.  Over the past 3 months, he has had progressive, bilateral lower leg pain that is worse with activity.  The patient began walking at age 19 months and has always walked on his toes.  He has had no fever, joint swelling, or rash.  The patient takes no medications, and his immunizations are up to date.  He was adopted as an infant, and his biological family history is unknown.  Examination shows bilateral calf enlargement and thin, atrophied thighs.  There is no focal tenderness with palpation.  The patient has a waddling gait.  His creatine kinase level is markedly elevated.  Muscle biopsy shows replacement of muscle by fat and connective tissue.  Which of the following additional tests should be performed at this time?

Quizplus · Accepted Answer

11ec25c8_d739_5be7_bc81_e99f02442530_MD0003_00 Duchenne muscular dystrophy (DMD) is an X-linked recessive disorder caused by a mutation in the dystrophin gene. Markedly reduced or absent expression of the dystrophin protein in skeletal and cardiac muscle fibers leads to severe, progressive muscle weakness. DMD should be suspected in a toddler boy with proximal lower extremity weakness and a history of delayed walking. Examination often reveals calf enlargement due to muscle replacement with fat (calf pseudohypertrophy), which can be associated with leg pain, as in this patient. To compensate for proximal muscle weakness, patients often walk their hands up their legs to help them stand (Gower sign). In addition, toe walking (due to tight heel cords) and a waddling gait are common. By early adolescence, most patients are wheelchair dependent, which can lead to scoliosis and restricted lung function. Gower sign Creatine kinase is markedly elevated in DMD, and the diagnosis is confirmed with genetic testing. If inconclusive, muscle biopsy is indicated and shows replacement of muscle by fat and fibrotic tissue. Echocardiogram and ECG are also required at the time of diagnosis to screen for dilated cardiomyopathy and conduction abnormalities, common complications of DMD caused by progressive fibrosis of cardiac muscle that can result in heart failure and death. (Choice A) Abdominal ultrasound is indicated in patients with WAGR syndrome to detect Wilms tumor. Other findings of WAGR syndrome (aniridia, genitourinary abnormalities, intellectual disability) would be expected and are not present in this patient. DMD is not associated with abdominal pathology. (Choices B and E) Antinuclear antibody testing and slit lamp examination (to screen for uveitis) are part of the management of juvenile idiopathic arthritis, which presents with chronic joint swelling, not muscle weakness. (Choice D) Skeletal survey may be performed to identify fractures, particularly if child abuse is of concern (eg, inconsistent history). Although patients with DMD are prone to fractures due to frequent falls, skeletal survey is not indicated in this patient with no focal bony tenderness suggestive of a fracture and no history concerning for child abuse. Educational objective: Duchenne muscular dystrophy should be considered in a toddler boy who has weakness, delayed walking, and bilateral calf enlargement. The absence of dystrophin in cardiac muscle can also lead to dilated cardiomyopathy and conduction abnormalities. Patients should be screened with an echocardiogram and ECG. References: Cardiac involvement in Duchenne muscular dystrophy and related dystrophinopathies. (http://www.ncbi.nlm.nih.gov/pubmed/29067654)

A 3-Year-Old Boy Is Brought to the Office by His