Uncharacterized neurologic disorders

[DocHoliday84]

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Question for practicing neurologists; how common do you guys think it is that someone has a neurologic disorder that is real but not yet characterized, ie. negative tests, symptoms and signs don't fit an established diagnosis, but yet there is an organic problem? I know that there is the diagnosis of functional neurologic disorder, but my impression is that this is thought to be nonorganic.

 

[deathmerchant]

Question for practicing neurologists; how common do you guys think it is that someone has a neurologic disorder that is real but not yet characterized, ie. negative tests, symptoms and signs don't fit an established diagnosis, but yet there is an organic problem? I know that there is the diagnosis of functional neurologic disorder, but my impression is that this is thought to be nonorganic.

That is difficult to say for certain because the line between functional and organic is blurry. I certainly see patients who I believe have a true neurological symptom, but either I don't know exactly what they have or I feel advanced testing is not going to be worth it (esp true for several genetic disorders) because I will treat them symptomatically anyways.
I would say about 20% of my patients have a functional disorder or more commonly a functional overlay to an underlying organic disorder.
What you are asking is probably <1% of cases.

 

[Spinothalamic]

Yeah, this is tough to answer. There are high-quality studies including from the NIH documenting “organic” objective findings in FND or chronic fatigue syndrome including actual difference in size of limbic structures on high-quality MRI. Additionally there seem to be statistically significant differences in various objective inflammatory markers in those who have what we call “long COVID” which often has clinical overlap with FND/chronic fatigue/fibromyalgia. Finally, remember that many psychiatric disorders are “organic” but we don’t understand how.

Anyway as to your actual question, I would say that in a couple of years of general neurology practice I haven’t seen a case that fits your description. Very rare. During residency at a quaternary care center there would be perhaps 2-3 cases per year referred for second opinion to undiagnosed diseases network due to truly undefined neurologic disorders. I was involved in a case where a “new” genetic disorder on whole exome with accompanying unique metabolomics profile presented in a young man with rapidly progressive dementia/spasticity and passed within a couple of years. There are other cases of clear paraneoplastic disorders without an identified antibody. Neuroimmunology labs around the world have stored many unique staining patterns of tissue immunofluorescence in these cases without a clearly defined antibody/target.