Another solution is that you could use consistent attribute syntax which seems most likely be turned into a CommonMark extension. E.g.
[My underlined text.]{ .clinical-term }
Although this may seem long-winded, the advantage is that is separates the styling from the structure of the document. Even if you always made the clinical-term class appear underlined (to preserve the meaning where this is referred to), it gives you options in the future if you want to, say, make all clinical terms appear in red to diffentiate them from other underlined text.