An 18-month-old boy is brought to the office due to developmental concerns. His parents have noticed that he does not walk independently, which worries them because his older brother began walking at age 12 months. The patient holds on to furniture while standing and steps sideways to move around. He can speak in 2- to 3-word sentences and follow simple commands. The patient can also build a tower of 6 cubes, drink from a straw, and feed himself table foods. Height, weight, and head circumference track at the 20th percentile, similar to prior visits. During physical examination, he uses his hands to push on his legs while getting up and seems to have pain when doing so. Which of the following is the best next step in evaluation of this patient?

Question

An 18-month-old boy is brought to the office due to developmental concerns.  His parents have noticed that he does not walk independently, which worries them because his older brother began walking at age 12 months.  The patient holds on to furniture while standing and steps sideways to move around.  He can speak in 2- to 3-word sentences and follow simple commands.  The patient can also build a tower of 6 cubes, drink from a straw, and feed himself table foods.  Height, weight, and head circumference track at the 20th percentile, similar to prior visits.  During physical examination, he uses his hands to push on his legs while getting up and seems to have pain when doing so.  Which of the following is the best next step in evaluation of this patient?

Quizplus · Accepted Answer

11ec25c8_d6e2_3a9d_bc81_95f714f7ddbd_MD0003_00 This patient has early signs of Duchenne muscular dystrophy (DMD), an X-linked recessive disorder that causes markedly reduced or absent dystrophin in muscle fibers. It is the most common muscular dystrophy in children and is characterized by severe, progressive muscle weakness. Typical presentation involves a toddler who has gross motor delay but demonstrates normal fine motor and language skills (as seen in this patient). Patients with DMD usually do not walk independently until age >18 months and often have difficulty running, jumping, and climbing stairs. Frequent falls and fatigue with activity are common. Gower sign, in which patients push their hands on their legs to assist in standing, is typically present from an early age due to proximal lower extremity muscle weakness and atrophy. By early childhood, calf enlargement due to muscle replacement by fat (ie, pseudohypertrophy) also develops. Progressive weakness leads to joint contractures, and most patients are wheelchair-dependent by adolescence. A creatine kinase level is the initial screening tool used to assess for myopathy and is markedly elevated in children with DMD. As the disease progresses, the creatine kinase level drops as more muscle is replaced by fat and fibrosis. Dystrophin gene mutation on genetic analysis is diagnostic. (Choice A) Brain imaging should be considered in patients with signs of cerebral palsy (eg, hypertonicity) or a neurodegenerative disorder (eg, global developmental delay). This patient's Gower sign and isolated gross motor delay are concerning for muscle pathology. (Choice C) Karyotype analysis detects Down syndrome, which often causes motor delay. However, patients also typically have language delay and dysmorphic features (eg, epicanthal folds, single palmar crease). In addition, Gower sign would not be expected. (Choice D) Reassurance is inappropriate for any child who cannot walk independently by age 18 months, particularly when Gower sign is present. (Choice E) An elevated TSH level suggests hypothyroidism, which can present with developmental delay, weakness, and decreased height velocity. In contrast, this patient's height has been tracking consistently along the 20th percentile. Educational objective: Duchenne muscular dystrophy presents with gross motor delay (eg, delayed independent walking), Gower sign, and progressive muscle weakness. Initial screening reveals elevated creatine kinase, and genetic analysis typically confirms the diagnosis. References: Muscle disease. (http://www.ncbi.nlm.nih.gov/pubmed/24488829) Growth and psychomotor development in patients with Duchenne muscular dystrophy. (http://www.ncbi.nlm.nih.gov/pubmed/24100172)

An 18-Month-Old Boy Is Brought to the Office Due to Developmental