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.

FND has been found to be one of the commonest reasons to see a neurologist.

• A study of 884 new outpatients in Australia found that 15% had a diagnosis of FND which was the third commonest diagnosis (Ahmad and Ahmad, 2016).
• A study of 577 new outpatients in neurology clinics in Aberdeen, UK found that 15% had FND making it the second commonest reason for an appointment after headache/migraine (Watila et al., 2022).
• In another older study of 3781 new appointments across Scotland, there were 209 patients who had clear FND and another 200 who had additional functional disorder diagnoses including dizziness and cognitive symptoms which could also be included now within FND (Stone et al., 2009). Other patients presented with diagnoses like migraine, but the neurologists thought the main issue was an associated functional disorder. So, anything from 6-16% of patients could be said to have a functional disorder depending on how that was defined. The upper limit of that estimate would make it the second commonest reason to see a neurologist. Since that study (which recruited between 2002 and 2004) recognition of FND has improved.
• A study from New Zealand found that 9% of all patients admitted to a neurology ward had FND (Beharry et al., 2021). Other studies from Oxford (7%)(Parry et al., 2006) and Berlin (9%) found similar numbers.

In Emergency Medicine settings FND is also common.

• A study of people with new seizures in an Australian emergency department found that around a quarter of people thought to have epileptic seizures, actually had functional seizures (seizures related to FND) (Lehn et al., 2021).
• The same study found that up to 50% of those with prolonged seizures had FND (Lehn et al., 2021)
• A study of stroke units in London found that around 8% had FND, and not a stroke (Gargalas et al., 2017).

How many people in the USA or UK have FND?

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).

References

Ahmad O, Ahmad KE. Functional neurological disorders in outpatient practice: An Australian cohort. J Clin Neurosci 2016; 28: 93–96.

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.

Nandi DN, Banerjee G, Nandi S, Nandi P. Is hysteria on the wane? A community survey in West Bengal, India. Br J Psychiatry 1992; 160: 87–91.

Parry AM, Murray B, Hart Y, Bass C. Audit of resource use in patients with non-organic disorders admitted to a UK neurology unit [6]. J Neurol Neurosurg Psychiatry 2006; 77: 1200–1201.

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.