An answer to a question on MedicalSciences.SE prompts my question. Suppose I live in Wisconsin and I fly to Texas to undergo a procedure with a specialist there (I chose the states arbitrarily; I'm not asking about state-specific laws).
So I have my procedure and fly back home. This procedure requires medications and months of follow-up care, which means I'll be receiving instructions from the Texas doctor and his staff, refills on prescriptions, and so forth. These interactions are all via phone or email while I remain physically in the state of Wisconsin.
I'm fairly sure all these interactions would be considered "practicing medicine" under the law. However, the Texas doctor is not licensed to practice medicine in the state of Wisconsin; and yet, that's exactly what he's doing.
How does the law view this? Do state laws typically make a specific exception for an ongoing doctor/patient relationship or is this covered only by case law? If it's based on case law, a citation would be a nice addition to an answer. Bonus points for adding how it would work if the specialist was in Europe instead of Texas.