Mr Jones is a 52 year old man with a 6 month history of muscle weakness mainly in the proximal lower limb muscles. His thigh muscles ache and his family have described his gait as ‘waddling’. His voice is unaffected and there are no problems with swallowing.
Examination findings concur with reduced power in the proximal lower limb muscles bilaterally and there is also some difficulty raising his arms. Deep tendon reflexes are reduced, and sensation is intact for both upper and lower limbs.
What is the most likely diagnosis?