A 70 year old man presents with asymmetric limb weakness. He complains that he often drops things with his right hand and cannot write, type, button, use zippers, or pick up small objects anymore. He also has a new onset foot drop which has caused him to trip and fall. On exam, you find increased reflexes and a spastic rigidity. You also notice some atrophy and fasciculations of the muscles.
Challenge: What's the diagnosis?