I did a bit of searching and found this-

[libel 1) n. to publish in print (including pictures), writing or broadcast through radio, television or film, an untruth about another which will do harm to that person or his/her reputation, by tending to bring the target into ridicule, hatred, scorn or contempt of others. ]
more - http://legal-dictionary.thefreedictionary.com/libel

Slander is a similar but verbal version.

If you have concerns about such, you can always just list the good & helpful doctors.
A doctor's name & city, state, or country would be best as there may be same or similar names that come up when others do only name searches..

PMs can be used to share more information.


Saying one is helpful, or not helpful is a pretty safe way to state your opinion.