Can you always definitely diagnose a stroke?

My mother had some leg numbness and says it now is weaker than her other leg. There were no additional symptoms that would point to stroke, but they did hospitalize her for tests. CAT scan , MRI and doppler of heart and carotid arteries did not show anything. Neither did blood tests. Dr. said it s possible that a small stroke can slip by. He didn t say it definitely was a stroke. I want my mom to look into other possible causes, such as something neurological -- possibly beginning of MS or anything -- just in case she should be getting treatment for something that isn t being diagnosed. She gets furious when I insinuate that it wasn t a stroke, because she is hell-bent that it was. She would prefer to just say she had a stroke, even though they didn t say it certainly was. Should you assume temporary leg numbness followed by weakness was a stroke when nothing else defines it as that? I d like to hear from anyone in the medical profession or anyone with a medical history of stroke.