Functional Neurological Disorder (FND) - articles, social media and discussion

There's a reason it's called a confusion matrix!

This article has 345 citations: Sensitivity, Specificity, and Predictive Values: Foundations, Pliabilities, and Pitfalls in Research and Practice (2017, Frontiers in Public Health) —

ETA: Interestingly if you look at Wikipedia's talk page, there are plenty of comments about how this is often used incorrectly and blaming the terms. Eg

ETA2: I think from now on I'm going to write as "true positive rate (sensitivity)" and "true negative rate (specificity)".

 

I was going to say until I got to the second sentence of the second para: if having Hoover's sign is how you define 'having FND' then of course you've given yourself a can't lose situation on that measure because what confirms 'that designation to the negative category was correct' is also the test on which you 'designated that category', it does feel like it flaws even the 'positives' because by such a test not checking whether there were more false negatives than positives - or indeed vice versa - I don't see how the test connects Hoover's sign with FND at all vs other conditions or explanations

it's slightly reminiscent of using the B12 test to see if someone has pernicious anemia. You'll get people with low B12 but that tells you probably how much B12 they are consuming doesn't it rather than about intrinsic factor and whether it is being used by the body - which is a different question and indeed diagnosis. Whatever people get on that B12 test any of them could technically have pernicious anemia as they aren't mutually exclusive.

If you were foolish enough to stop the treatment and investigations there and conclude that because both sets: those with pernicious anemia and the ones you've fished out due to having low B12 presented with the same 'other symptoms' you want to list in the short term and try and use an ergo this means my non-longitudinal study (not repeated after treating those who merely have insufficient B12 in their diet and just needed supplementation) proves this test to be the definition of the condition. Based quite on what? fallacy of the numbers in this set-up and sample look 'feasible/about what we predict it would be if this worked' (always misleading way to judge research) and 'those in the designated positive seem to have symptoms'

 

There are multiple ways to express the two constructs. In fact, what I have is the same as what wikipedia has, but written differently. The wikipedia definitions look backwards to me but actually represent the same thing. But it took me a while to work this out and I had to consult with an epi colleague.

 

Erm isn't this even confused in their own selling it to themselves when they diss functional medicine as 'very different and quackery' compared to those woh 'treat conversion disorder' noting that functional medicine works because even a placebo can help, when isn't erm the whole area of those who treat conversion disorder based on leveraging placebo effect obsessively, and basing their research on maximising it (even though placebo isn't 'the mind of the patient' but trial and investigator bias)?

 

I think I've got my head around this a bit better now.

Let's rewrite that as two separate sentences and then just concentrate on the first —

1. Specificity is a measure of whether a true positive case is correctly identified by a positive test.
2. Sensitivity is a measure of whether a true negative case is correctly identified by a negative test.

As up-thread, Specificity is defined as the true negative rate, ie number of true test negatives / number of people without condition. However, mathematically this is also 1 - False Positive Rate. FPR = 1- TNR (written as TNR = 1 - FPR on Wikipedia). Therefore Specificity is also a measure of the false positive rate.

When we're talking about very high specificity the False Positive Rate approaches 0. 100% specificity (TNR) = 0% FPR. A low or zero False Positive Rate means that a positive test correctly identifies a positive case (always or nearly always). Which is what sentence #1 says above.

(You can do the same for #2 as Sensitivity = True Positive Rate = 1 - False Negative Rate.)

Many years since I last thought about this stuff, but I guess this is why errors seem to be "reversed": because it's "1-x", where x is the measurement of the test behaving properly. So the end result is: high sensitivity = low type II error rate; high specificity = low type I error rate. (Type I error is a false positive and type II error is false negative).

 

Reading that sentence makes me think that there may be a tautology in the original wording. I think the term "true positive case" is incorrect. The case is a binary - it's either positive or negative (person has disease or doesn't, truly for either). Only the test can be true/false in its assessment of positive or negative. Ie. giving four options: true positive, false positive, true negative, false negative.

 

They're hypocrites (The worst in medicine) just like that Pseudoskeptic Ben Goldacre.

 

Given my own experience with being diagnosed with FND, I'd say that neurological diseases can certainly be very hard to diagnose if you don't, uh, carry out the tests that can detect them. That diagnosis gets even harder if you combine that lack of diagnostics with an assumption based on personal biases that the patient likely has FND.

Every thread about FND on here quite rightfully hones in on the supposed use of 'positive signs', which FND's main proponents loudly profess as to being key to accurately diagnosing FND....nowadays, anyway. In reality it seems that quite a few neurologists are still (2020-2023) willing to diagnose you without any 'positive signs' and without ruling out known neurological diseases by doing appropriate testing.

I had 3 different neurologists - including an FND 'specialist'* and a very senior notable (in the area of neuropathy) neurologist all confidently declare I had FND on the basis of only basic testing and talking to me. Now, the last one also correctly identified the actual physical problem I was eventually diagnosed with (a little later, elsewhere) as a possibility but decided during the consultation and before the actual further testing he wanted that while I might have the physical disease I also had FND/FND 'overlay'**.

Now, leaving aside the last one, you'd think that when a patient comes to you complaining of blatant neuropathy symptoms that you would do everything you could to exclude neuropathy as a cause before moving onto the mysterious, messy, barely-evidenced magical realm of FND. Well, you'd be wrong, in my case and in the cases of many other neurology patients, based on my research online.

I'm a layperson. I shouldn't be able to diagnostically out-perform several neurologists (there were others prior to the 3 who diagnosed FND) just by doing some reading online and reflecting on my symptoms. But I did outperform them, both in correctly identifying what was wrong with me and in identifying the necessary diagnostic testing that I needed. I mean needed both in the sense of confirming my own personal theory and surely needed as part of a workup by any professional worth their name that actually wanted to exclude known neurological disease.

What I've discovered after struggling through a health nightmare consisting of multiple terrible symptoms that were investigated by many departments at many hospitals over many years is that, frankly, the medical field seems to be in a state of disarray, particularly neurology. It is a miracle that i'm still here given what I've been through. Despite that, my symptoms seem minor compared to what many of you have to live with, which is humbling - and frightening.

*I was referred to the FND specialist after questioning and objecting to the FND diagnosis. She took an extensive history from me and asked me about my mental health. She requested no further testing. She just rubberstamped the prior FND diagnosis, which in retrospect she was clearly asked to do by the original neurologist. I very naively hoped that she would be more thorough and request more tests including the ones that I knew that I needed to get. Nope.

**As has been noted here many times in threads discussing FND, it seems that you cannot escape the FND diagnosis even if you are diagnosed with clear physical disease before or after you receive it. Or, in my case, during the first tentative diagnosis of the physical disease! Wherever you turn; there's FND.

 

Right. It's like if they find something else, it's a get-out-of-jail-free card--well, we were right, you did have FND and you still do as a co-morbidity or as an "overlay." Basically, it's unfalsifiable.

 

Thanks. I've been reading the forum for days, going over threads mentioning FND but also broadly anything related which obviously covers all the BPS, psychosomatic stuff that you are all quite rightly very interested in. When I first discovered this forum I was very excited because I'd been trying to find somewhere I could read normal people discussing FND. It turned out to be a goldmine.

There were so many good posts and quotes I wanted to reply to and I didn't know where to start. I don't have ME or CFS, at least I don't think so. But given that I have an unusual neurological problem that still hasn't been fully explained, was diagnosed with FND and find the FND diagnosis to be highly dubious to say the least I thought I had something to offer the discussions here.

So, just to be clear I wasn't diagnosed by the third neurologist mentioned above, he just floated my eventual diagnosis as a possibility.

After him and the above I was later diagnosed with a physical neurological disease using objective physical evidence at an entirely different hospital, on an entirely different 'track' through the NHS. None of the neurologists I saw there ever mentioned FND. Curious! From the start, things felt different with them.

If I'd stuck solely to the original neurological 'track' I was on (by which I mean a chain of referrals) and accepted the FND diagnosis I never would have gotten any physical proof of any physical disease. But the moment the neurologist told me I had FND over the phone I instantly realised this was a psychosomatic diagnosis.

I looked at neurosymptoms.org at that neurologists urging and for all the many reasons discussed at length on this forum I was utterly, totally unconvinced by the concept of FND. Worse still, I knew that I hadn't received appropriate testing to rule out the most obvious cause of (some) of my symptoms and I hadn't been diagnosed on the basis of any 'positive signs' anyway.

Just to add a little more detail I am a man. I mention that because I am aware of how gendered the application of the psychosomatic illness label is or can be.

 

It’s the insurance industry’s El Dorado. Sure you have a harrowing disease, but the symptoms are caused by a concomitant functional disorder. Thus, a little rehab and back to work you malingering reprobates!!

 

Welcome @Gradzy thanks for sharing your story

 

Hi @Gradzy I'm sorry medicine failed you so badly initially but am pleased they are on track for you now. Your story in isolation is a goldmine - talk about a postcode lottery of medical care!