I think you should be fine unless you spent 6 or more months in a designated country in the past year. This is usually the case for developing countries. CIC has a list of those countries. If you stayed in Canada for the entire period, you should be fine. During the study permit extension questionnaire, they will ask you if you have had a medical exam done and the next question will be if you have lived in a designated country. Check the list and if you haven't then you are all set. I did the same and got mine extended with no issues.