A truly stifling medical condition, or reason to be on alert for FMLA fraud?

Q: I have an employee who is off on FMLA leave. I have his certification and it states that he has chronic, unpredictable diarrhea with stool incontinence. I asked for clarification and the doctor wrote if he can do his job from the bathroom, then he can work. He also came in with a slip wanting intermittent leave so he could leave work if need be to get cleaned up. I told him that I would not approve the intermittent FMLA. The other employees think he just wants the summer off. He has a brand new deck on the side of his home and he comes in with sunburn like he's been working on his farm. His FMLA was approved under Absence with Treatment. I talked to my supervisor and she does not want to send him to a doctor of ours for a second opinion at our expense. What can I do about this? – Dorothy, Michigan