I would not be surprised if there is such a patient or even more than one.
Many times there is no effective treatment which alters the course of neurological diseases. The only treatment available is symptomatic and supportive care.

Think about ALS-with or without a diagnosis there is no effective treatment to alter the course of this illness.
You can send them home and tell them that their symptoms are caused by emotional problems.
Or: you can give them a wheelchair, help them arrange their house to fit their needs, provide respiratory support early on, help them keep leading a productive life etc. etc.

Guess what would be the outcome of the first patient as compared to the outcome of the second patient? The second patient will have a much better quality of life and will live much longer (this is supported by the medical literature).

You do not need a diagnosis in order to treat a patient with respect and do your best to improve their quality of life and prolong their life.

I can understand being reluctant to give immunosupressive treatment (which has potentially serious side effects) without a firm diagnosis. I can't understand easily giving tranquiliziers or other psychiatric medications (which have potentially serious side effects and risk of addiction) without having a firm proof that those are required. I can't understand neglecting a patient without a firm diagnosis.

I believe there are neurologists who do not see the diagnosis of CD as a reason to neglect or even punish the patient. I know there is at least one who thinks that such patients require treatment and support. He still used the term "functional neurological symptoms" (which has different meaning for different people and is a very deceiving term in my opinion) but I believe he does help at least some of his patients.

http://www.neurosymptoms.org/#/stories/4533053414

The problem with his approach is that it makes this diagnosis more legitimate, leads to less interest in trying to understand the underlying causes of those "unexplained" symptoms, but at least it leads to a more humanistic approach to those patients. It can be a step forward, or a step backwards (he was one of those who pushed towards the new DSM-5 category, which shows that he himself doesn't see "functional/CD as a true neurological disorder, or else why would it appear as a psychiatric diagnosis in a psychiatric manual?)

Also, his patients may be deprived of proper treatment and supportive care because he lumps them all under one category and gives them a "one size fits all" treatment.
For instance, an MG patient with normal test results who is diagnosed as CD would be treated with human respect but at the same time be encouraged to exercise, would not receive mestinon and similar medications and would quite likely receive tranquilizers and not respiratory support if required. This patient (mostly if he was met with disbelief and disrespect previously) may be satisfied, because he/she doesn't know better.