Contemporary positive signs of functional limb weakness in post-acute sequelae of SARS-CoV-2: an exploratory analysis…, 2025, Osada et al.

Jonathan Edwards said:
Sorry, David, but I think you have misunderstood here. If rule in signs are valid the absence of relevant symptoms is not a problem or even an anomaly. It is not uncommon. The interpretation of these signs may be confused or wrong but you don't need to have a symptom for them to be meaningful.
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Can you explain how that works?

And I don’t think these rule in signs been validated in any way?
 
Utsikt said:
Can you explain how that works?

And I don’t think these rule in signs been validated in any way?
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The signs are reasonably sensible as tools to make a diagnosis in the same way that all other neurological signs are. They are validated in that on most occasions their presence is taken to exclude a particular anatomical defect, the absence of which is confirmed with MRI or whatever.

They are no doubt misused but I don't have any information on that one way or the other.

The problem comes with the diagnosis. If FND means an apparent neurological deficit in the absence of any evidence of structural abnormality, presumed due to some abnormal nerve signalling in the forebrain, then I don't see any real objection. If it is used to imply something like conversion disorder then it is bogus.

But ther patient might present with a headache or a rash or just about anything and still have a rule in FND sign. Let us say that they fail to lift the right leg when you ask them to but also fail to have a normal reflex contraction in the other leg. That means that the failure of the lifting of the right leg i due to some problem in signalling in the forebrain, not in the leg. So you can diagnose FND. They don't have to have compained of leg weakness.

This is a perfectly real situation. Patients show these signs without the relevant symptom.
 
Jonathan Edwards said:
The signs are reasonably sensible as tools to make a diagnosis in the same way that all other neurological signs are. They are validated in that on most occasions their presence is taken to exclude a particular anatomical defect, the absence of which is confirmed with MRI or whatever.
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Have you seen a study of these FND positive signs that actually did an extensive check for structural abnormalities or other alternative explanations?
 
Utsikt said:
Have you seen a study of these FND positive signs that actually did an extensive check for structural abnormalities or other alternative explanations?
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No but have you seen such a study for all the signs normally used by neurologists to make diagnoses? Neurologists learn the validity of these signs as trainees doing full neurological examinations up to ten times a day, making a clinical diagnosis and the seeing if it is confirmed by imaging and neurophysiology etc.

I don't see any reason to doubt that the signs show an absence of a local peripheral lesion - which is the point of the operational FND diagnosis. I don't know how many patients I have examined but I did six months as a full time trainee neurologist and it must have been hundreds. In other contexts the neuro exams I have done must run into many thousands. Do we have studies confirming that the tests run by mechanics to distinguish a blocked fuel feed from a dirty plug are reliable? Once a mechanic has got 200 engines going again he tends to be pretty reliable.
 
FND patients are educated on ingnoring symptoms,
But when the patients have done the ingnoring on their own we can always blame @dave30th ?

Neuro exams? no 1 stuck a needle in my upperleg and the leg was air-cycling on it's own. Normal? He could not help me.
No 2 was blinded by ME/CFS in the illness history and could not find a simple infection in my hand. No 3 could find it, not blinded.
No 4 left me with no less than 3 options.
Just in my country?
 
Jonathan Edwards said:
No but have you seen such a study for all the signs normally used by neurologists to make diagnoses? Neurologists learn the validity of these signs as trainees doing full neurological examinations up to ten times a day, making a clinical diagnosis and the seeing if it is confirmed by imaging and neurophysiology etc.

I don't see any reason to doubt that the signs show an absence of a local peripheral lesion - which is the point of the operational FND diagnosis. I don't know how many patients I have examined but I did six months as a full time trainee neurologist and it must have been hundreds. In other contexts the neuro exams I have done must run into many thousands. Do we have studies confirming that the tests run by mechanics to distinguish a blocked fuel feed from a dirty plug are reliable? Once a mechanic has got 200 engines going again he tends to be pretty reliable.
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That seems to be recipe for all kinds of bias.

And the mechanics have access to the schematics of the cars because we built them. Aren’t humans vastly more complex?
 
Utsikt said:
That seems to be recipe for all kinds of bias.

And the mechanics have access to the schematics of the cars because we built them. Aren’t humans vastly more complex?
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Any indirect assessment is open to bias, but why should there be if the objective is make a useful prediction and you repeatedly have validation by imaging?

The nervous system as assessed in a neurological examination is not more complex than a car probably. You check for peripheral nerve failure, motor and sensory, spinal pathway failure, and failure in about ten brain regions. Diseases tend to be distinguishable by assessing those compartments. Things get more complicated when it comes to thinking and memory but then we are already up in the cortex. The rule in signs are signs that the problem is up in the cortex.

I don't particularly recommend basing a diagnosis on rule in signs but there is nothing inherently suspect about them, any more than any other clinical assessment. They are different in that what they rule in is 'we don't know what is going on'.
 
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