The answer to this question depends on what data you look at. As this has been an area that has led to confusion, I’ve laid out some of the studies below. Sorry it’s a bit technical. The bottom line is that FND is one of the commonest conditions in neurology, but it’s been hidden from view, and a lot more people have it than most people realise.
This is a hard question to answer accurately but an estimate can be made by looking at the two most common types of FND, functional seizures and functional movement disorders (including limb weakness and stroke-like presentations). If the best estimates of those conditions (Duncan et al., 2011)(Villagrán et al., 2021) are put together with studies of children and young people (Hansen et al., 2020) (which don’t appear in the same studies), along with studies that tell us how long, on average people have FND symptoms for, then we end up with a figure of between 250,000-500,000 in the US and around 50-100,000 in the UK. The true number may be less than that, but it also could be a lot more.
Another recent study from general practice (family doctors) covering 72% of people in Scotland found that FND had been diagnosed in 8040 people. That would be equivalent to 11,150 people in Scotland and around 140,000 people in the UK.
Most neurologists acknowledge that FND is underestimated in clinical services as its often poorly coded by hospital administration systems. In some parts of the world, neurologists don’t receive payment if they use existing codes for FND which reduces estimates (Stone et al., 2014). Better studies would be welcome to gain a more accurate idea of the precise numbers, but it’s clear that it’s a common problem.
In the US a study of costs of FND showed that it was consuming over $1 billion dollars in inpatient costs a year – similar to motor neuron disease/ amyotrophic lateral sclerosis (Stephen et al., 2021).
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Beharry J, Palmer D, Wu T, Wilson D, Le Heron C, Mason D, et al. Functional neurological disorders presenting as emergencies to secondary care. Eur J Neurol 2021; 28: 1441–1445.
Duncan R, Razvi S, Mulhern S. Newly presenting psychogenic nonepileptic seizures: Incidence, population characteristics, and early outcome from a prospective audit of a first seizure clinic. Epilepsy Behav 2011; 20: 308–311.
Gargalas S, Weeks R, Khan-Bourne N, Shotbolt P, Simblett S, Ashraf L, et al. Incidence and outcome of functional stroke mimics admitted to a hyperacute stroke unit. J Neurol Neurosurg Psychiatry 2017; 88: 2–6.
Hansen AS, Rask CU, Rodrigo-Domingo M, Pristed SG, Christensen J, Nielsen RE. Incidence rates and characteristics of pediatric onset psychogenic nonepileptic seizures. Pediatr Res 2020; 88: 796–803.
Lehn A, Watson E, Ryan EG, Jones M, Cheah V, Dionisio S. Psychogenic nonepileptic seizures treated as epileptic seizures in the emergency department. Epilepsia 2021; 62: 2416–2425.
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Stephen CD, Fung V, Lungu CI, Espay AJ. Assessment of Emergency Department and Inpatient Use and Costs in Adult and Pediatric Functional Neurological Disorders. JAMA Neurol 2021; 78: 88–101.
Stone J, Carson A, Duncan R, Coleman R, Roberts R, Warlow C, et al. Symptoms ‘unexplained by organic disease’ in 1144 new neurology out-patients: how often does the diagnosis change at follow-up? Brain 2009; 132: 2878–88.
Stone J, Hallett M, Carson A, Bergen D, Shakir R. Functional disorders in the Neurology section of ICD-11: A landmark opportunity. Neurology 2014; 83
Villagrán A, Eldøen G, Duncan R, Aaberg KM, Hofoss D, Lossius MI. Incidence and prevalence of psychogenic nonepileptic seizures in a Norwegian county: A 10-year population-based study. Epilepsia 2021; 62: 1528–1535.
Watila MM, Duncan C, MacKay G. Evaluation of telemedicine for new outpatient neurological consultations. BMJ Neurol Open 2022; 4: 1–8.
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