Q. A 50-year-old man comes to the physician’s office for difficulty in walking and standing up from a seated position for the past 2 years. In the beginning, symptoms were limited to lower limbs, but for the past year, he is observing difficulty in combing his hair, opening the door, and difficulty in swallowing. He is too tired to do his usual activities or even to get out of bed. His temperature is 98.4°F (36.9°C), pulse is 91 beats per minute, BP is 120/80 mm of Hg and respiratory rate is 15/min. Physical examination shows the weakness of hip flexors, quadriceps, ankle dorsiflexors, and distal finger flexors with corresponding atrophy. The creatine kinase level is 352 U/L. Electromyography shows reduced muscle action potentials. Muscle biopsy shows mononuclear cell infiltrates in non-necrotic muscle fibers, and canonical rimmed vacuoles with tubulofilaments on electron microscopy. What is the most likely diagnosis for this patient?