Clinical Reasoning: An unusual cause of transverse myelitis?

A 71-year-old woman presented with a 1-week history of progressive weakness involving her lower extremities, leading to an inability to walk. She also noticed diminished sensation in her lower extremities. She did not complain of bowel or bladder dysfunction. She did not have any neurologic symptoms in her upper extremities. She experienced an upper respiratory tract infection 5 days prior to the start of these symptoms and was treated with antibiotics. There was no history of headache, impaired cognition, or speech impairment.