Some doctors withhold info if they think the info might further upset the client. I, personally, feel they should be 100% honest if a client asks.
If a client is diagnosed with a condition, not only should the client know the condition(s), but also should be fully informed of all treatment options. Many therapists treat with their own modality, whatever s/he is trained in, without truly informed consent as to what they are treating, which modality is being used, which modality has the highest success rate, etc.
I believe everyone deserves fully informed consent when it comes to diagnoses and to treatment.

WC