A 3-year-old boy is brought to the office by his parents for evaluation of lower extremity weakness. His mother states, "He used to be able to play soccer with his older sisters for hours, but for the past several months, he stops playing after 10 minutes because his legs feel tired." The patient has also been "clumsy" recently and frequently trips while walking. He has no joint pain, incontinence, constipation, numbness, or systemic fatigue. Language development is slightly delayed, and he learned to walk at age 18 months. He has had no chronic medical conditions or surgeries. The patient takes no medications and has received all recommended vaccinations. His aunt has Hashimoto thyroiditis; family history is otherwise noncontributory. Vital signs are normal for age. Physical examination shows a cooperative, nondysmorphic boy. Both calves appear large in circumference compared to the thighs. Strength is 3/5 in the bilateral quadriceps and 4/5 in the calves. Sensation is intact. Achilles deep tendon reflexes are hyporeflexic. The patient walks with a waddling gait. Which of the following is the best next step in management of this patient?

Question

A 3-year-old boy is brought to the office by his parents for evaluation of lower extremity weakness.  His mother states, "He used to be able to play soccer with his older sisters for hours, but for the past several months, he stops playing after 10 minutes because his legs feel tired."  The patient has also been "clumsy" recently and frequently trips while walking.  He has no joint pain, incontinence, constipation, numbness, or systemic fatigue.  Language development is slightly delayed, and he learned to walk at age 18 months.  He has had no chronic medical conditions or surgeries.  The patient takes no medications and has received all recommended vaccinations.  His aunt has Hashimoto thyroiditis; family history is otherwise noncontributory.  Vital signs are normal for age.  Physical examination shows a cooperative, nondysmorphic boy.  Both calves appear large in circumference compared to the thighs.  Strength is 3/5 in the bilateral quadriceps and 4/5 in the calves.  Sensation is intact.  Achilles deep tendon reflexes are hyporeflexic.  The patient walks with a waddling gait.  Which of the following is the best next step in management of this patient?

Quizplus · Accepted Answer

Explanation: 11ec2b69_c184_827c_8f63_29613a8066c4_MD0005_00 This patient's age, developmental delay, lower extremity weakness, and apparent increase in calf diameter are typical of Duchenne muscular dystrophy (DMD). DMD affects boys who have a defective dystrophin gene on the X-chromosome. DMD presents with weakness of the proximal lower extremity muscles in boys age 2-3. Symptoms include difficulty walking, running, jumping, and climbing stairs. Patients may push their arms on their thighs (Gowers sign) to transition from sitting to standing. As fatty tissue replaces degrading muscle, examination shows pseudohypertrophy of the calves, hyporeflexia of the Achilles tendons, and a waddling gait. Additional complications include progressive dilated cardiomyopathy and scoliosis. DMD is associated with mild intellectual disability and global developmental delay. (Gowers sign) If DMD is suspected, a serum creatine kinase (CK) level is indicated as CK is released with muscle inflammation or damage. Muscle biopsy is not required for diagnosis but will show fibrosis, fat, and muscle degeneration in patients with DMD. Genetic testing showing deletion of one or more exons of the dystrophin gene confirms the diagnosis. (Choice A) Acetylcholine receptor antibodies are present in myasthenia gravis (MG), which can present with proximal muscle weakness. However, patients with MG typically have upper extremity involvement and ocular weakness (eg, ptosis, diplopia). In addition, although neonatal and juvenile MG can occur, MG is most common in adults. (Choice C) Disorders of the spine (eg, Guillain-Barré syndrome, transverse myelitis) can also lead to lower extremity weakness, hyporeflexia, and gait abnormalities. However, spinal lesions also typically trigger sensory symptoms (eg, numbness) and bowel/bladder dysfunction, not seen in this patient. Imaging of the spine could be considered if CK is normal. (Choice D) Nerve conduction studies can aid in the diagnosis of peripheral nerve disorders (eg, diabetic neuropathy), which typically present with distal, not proximal, weakness and sensory symptoms (eg, tingling, pain). (Choice E) Untreated, long-standing hypothyroidism, as indicated by an elevated TSH level, can present with myopathy but is unlikely given this patient's age and absence of additional symptoms (eg, fatigue, constipation). Educational objective: Duchenne muscular dystrophy is an X-linked myopathy that typically presents with proximal lower extremity weakness (eg, difficulty walking, Gowers sign) and bilateral calf enlargement in toddler boys. Serum creatine kinase is markedly elevated, and genetic testing can confirm the diagnosis. References: Duchenne muscular dystrophy. (http://www.ncbi.nlm.nih.gov/pubmed/25752877) Duchenne and Becker muscular dystrophies. (http://www.ncbi.nlm.nih.gov/pubmed/25037084)

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