MRCP2-3478

MRCP2-3478

A 15-year-old comes to your neurology clinic complaining of progressive weakness in his lower limbs that has been gradually developing for the past 10 months. He has noticed difficulty keeping up with his peers during physical education classes for the past year and a half, which he initially attributed to his lack of athleticism. However, he now experiences weakness when walking and has particular difficulty rising from a seated position.

During the examination, you observe significantly enlarged calf muscles. Formal power testing reveals 4- out of 5 in bilateral shoulder abduction and adduction, with normal 5 out of 5 distally. Additionally, 4- out of 5 is noted in hip flexion and extension, 4+ in knee flexion and extension, and 5 out of 5 in ankle plantar and dorsiflexion. The weakness is not fatigable and is persistent. Reflexes are present in all areas, and plantar reflexes are downgoing. The patient has no significant medical history, and his family history is unknown as he was adopted. What is the most likely diagnosis?