Is this a real case? Published or someone shared their story with you? This is a good example of why patients diagnosed with FND should have longitudinal care with neurology - the standard of care. Vast majority will continue to just have FND but there is a small percentage of people, particularly older adults, who may have a change in clinical presentation requiring diagnostic revision. It’s important to note that these examples are not examples of misdiagnosis. At the time of diagnosis, it sounds like this patient was not presenting with typical signs of PSP. Sometimes neurological diseases need time to progress for the clinical picture to become clear. In these cases, the initial diagnosis of FND isn’t really harmful because there is nothing you can do to slow progression of PSP and FND rehabilitation could still be beneficial. It sounds this her medical team did a good job reassessing her symptoms as they progressed, ordered additional testing that was indicated, and revised the diagnosis that fit the clinical picture. Unfortunately the people who visit this site won’t understand this and will use it as evidence that they were misdiagnosed and have a terminal neurodegenerative disease.

I answered your question regarding what would falsify a clinical diagnosis of FND. The clinical diagnosis of FND can be falsified or weakened by evidence such as:

1. The positive signs are absent, incorrectly elicited, or misinterpreted.
2. The symptom pattern is better explained by another disorder.
3. The supposed inconsistency is actually consistent with known physiology.
4. Longitudinal data contradict the diagnosis.
5. The diagnosis was made only because tests were normal.

Again, none of those apply to this case which is why FND was kept as a comorbidity and is not considered a misdiagnosis. The authors propose maybe a CSF leak could cause these FND symptoms but then contradict themselves by clearly stating it could not cause the motor symptoms and that the motor symptoms are consistent with FND.

Parkinson’s Disease and migraines are both clinical diagnoses and diagnosed the exact same way as FND - presence of characteristic features in the history and examination. Parkinson’s is not diagnosed based on biomarkers. We can verify the diagnosis with an autopsy after death but we are talking about clinical diagnosis so it is the same as FND in this scenario.

The authors do a great job explaining their rationale for the FND diagnosis and why the incidental finding could not explain the motor symptoms. It is odd that they then say “functional appearing symptoms” when they just concluded she did have FND and the structural finding is most often asymptomatic. Resolution of symptoms after surgery, is not sufficient evidence to conclude the CSF leak was causing the clear FND symptoms. It is well known that surgery can lead to large placebo effects. It is not unreasonable to hypothesize that being given a structural diagnosis as an explanation for previously unexplained symptoms (they said she was never told she had FND) and having the structural defect corrected likely contributed to updating the brain’s prediction model. It’s also possible that the CSF leak could have caused some of her symptoms like headaches which indirectly contributed to the FND symptoms. FND symptoms are mediated by attention and so other health conditions can lead to excessive attention towards the body which contributes to the development and maintenance of FND. Take away the other symptoms by correcting the structural defect and you are likely to see improvement in FND symptoms. It is reasonable to think both of those explanations were at play here. The danger here is thinking this means we should overly investigate and surgically correct all incidental findings. That will lead to more harm. It is also possible that her FND symptoms could return in the future under certain circumstances.

Regarding the question you propose at the end: FND would be invalidated if she didn’t have FND symptoms…but she had all the textbook FND symptoms which cannot be explained by a CSF leak. If this were Parkinson’s disease or migraines, would you ask the same question?

The scientific construct of FND is falsifiable: FND models make testable claims regarding altered agency, attention, prediction, motor control, interoception, threat/arousal regulation, and abnormal integration of sensory-motor predictions. These claims can be tested with behavioral experiments, neurophysiology, imaging, treatment-response studies, and predictive-processing/active-inference models.

The FND diagnosis can be falsified or weakened by evidence such as:

1. The positive signs are absent, incorrectly elicited, or misinterpreted.
2. The symptom pattern is better explained by another disorder.
3. The supposed inconsistency is actually consistent with known physiology.
4. Longitudinal data contradict the diagnosis.
5. The diagnosis was made only because tests were normal.

In this case, none of that applies but if it did it would invalidate the FND diagnosis. This case is a good example of comorbidity and the importance of treating comorbidities (although it is questionable here if the CSF leak truly needed to be repaired) but it doesn’t tell us anything about the validity of FND.