WebPathLab has an expandable English and Medical Dictionary.  You can load your own medical dictionary or us the once provided by WebPathLab.

The dictionary actually learns as you add more words to its vocabulary so that you need enter a new term only once.

 The system will automatically highlight the mis-spelled word in yellow, the user clicks on the word and a menu appears where the corrected word can be selected, or the current word be added to the dictionary for future use.  If the word is added to the dictionary, it will not be highlighted again as mis-spelled.