A 59-year-old man presents to the ED for acute onset low back pain that started immediately after he moved furniture. He states his lumbar pain has been unrelenting, with mild pain radiating to down both legs. He appears in pain and has mild midline and bilateral paraspinal tenderness to palpation over his lumbosacral spine. He has bilateral loss of strength in the distal lower extremities, notably in dorsiflexion. What diagnoses should you consider?