Question:
A 1-year-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 the evaluation of this patient?

A. Brain imaging
B. Creatine kinase level
C. Karyotype analysis
D. Reassurance only
E. Serum TSH level

Answer:

Correct Answer: B. Creatine kinase level

• This 1-year-old boy is demonstrating developmental delay with delayed walking (not walking independently by age 1), which could indicate muscular or neurological concerns.

• His behavior of using his hands to push on his legs when getting up and the associated pain suggests a possible underlying neuromuscular disorder, such as muscular dystrophy.

• Creatine kinase (CK) levels are elevated in muscular dystrophy due to muscle breakdown.

🧠 Muscle Weakness in Lower Extremities 

⬇️
Genetic Mutation in Dystrophin Gene
(Dystrophin stabilizes muscle cells; mutations lead to its deficiency) 

⬇️
🧠 Dystrophin Deficiency
⬇️
Muscle Cell Membrane Instability
⬇️
🧠 Repeated Muscle Injury and Repair Attempt
⬇️
Myocyte Degeneration
⬇️
Creatine Kinase (CK) Levels ↑
⬇️
Muscle Weakness and Delayed Motor Milestones
(Delayed walking as in the case scenario)
⬇️
🧠 Gower's Sign (uses hands to push on legs due to weak proximal muscles)

⬇️
Recommendation: Measure Creatine Kinase (CK) Level (Correct Answer: Option B)

Explanation of Other Options

A. Brain Imaging
(Incorrect)
(Pathology differs: Brain imaging is indicated if there are concerns of central nervous system issues like hydrocephalus or cerebral palsy, which present differently with cognitive and global developmental delays rather than selective motor delay as seen here).

C. Karyotype Analysis
(Incorrect)
(Relevant for suspected chromosomal disorders like Down syndrome, where facial dysmorphisms, intellectual delays, and cardiac anomalies are usually evident. This patient lacks such features).

D. Reassurance Only
(Incorrect)
(Although there is some variation in walking milestones, Gower’s sign and delayed motor function suggest a pathological cause, thus requiring investigation rather than reassurance).

E. Serum TSH Level
(Incorrect)
(Hypothyroidism can cause developmental delay but usually presents with hypotonia, lethargy, and growth delay rather than isolated motor weakness or Gower’s sign).

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