Mahinda Yogarajah Functional dissociative seizures (FDS) are paroxysmal, time‐limited alterations in motor, sensory, autonomic, and or cognitive signs and symptoms. Superficially, they may resemble epileptic seizures, but they are not caused by epileptic activity.1 FDS are beyond voluntary control, and fulfil the diagnostic criteria of dissociative disorder (ICD‐10), or conversion (functional neurological symptom) disorder (DSM‐5). The most appropriate term for these episodes is controversial. Historically, the term psychogenic nonepileptic seizures has been used. Currently, the International League Against Epilepsy (ILAE) favours the term FDS. The incidence of FDS is approximately 3/100,000/year,2 as common as multiple sclerosis. The prevalence ranges from 24 to 109/100,000.3 These figures are likely underestimates, as most studies are based on cases confirmed by video‐EEG telemetry and usually exclude those with comorbid epilepsy. FDS is the second most common diagnosis made in an epilepsy clinic. In a large UK cohort with FDS, the modal age at onset was 19 years, with a median age of 28 years. The male‐to‐female ratio varied by age at onset, with 77% of participants being female; however, only 59% of males developed FDS by age 40 years. Thus, the proportion of males increased with age at onset. More than half lived in deprived areas, and over two‐thirds were unemployed.4 Rates of comorbid epilepsy are 12‐22%, particularly in those with drug‐resistant epilepsy (DRE).5 A correct FDS diagnosis may take years, with inappropriate treatment with antiseizure medications (ASM). Nearly ten per cent of people in two large status epilepticus trials had prolonged FDS.6 The cost of undiagnosed FDS can exceed the cost of treating epilepsy over the lifetime of an individual. Additionally, significant socioeconomic costs are associated with lost workdays, unemployment, and constraints on quality of life. People with FDS have significantly elevated premature mortality rates, comparable to those with DRE.7,8 The premature mortality risk in people with FDS is up to 5.5 times higher than that of the general population. Medical and psychiatric comorbidities may contribute substantially to this risk, but the increased mortality remains even after accounting for socioeconomic factors and psychiatric comorbidities. Causes such as suicides and accidental poisonings, are major contributors, particularly in younger people,7,8 comparable to epilepsy alone.9 Sudden unexpected death is common, though the reasons remain unclear.8 An early diagnosis is associated with improved seizure control and quality of life. A diagnosis is typically based on seizure semiology, the individual’s subjective experience of the seizure, and their description of the event. However, it is unclear whether this reliably applies in children, individuals with intellectual disability, or those with FDS and epilepsy. FDS are often frequent, and the lack of improvement in seizures despite appropriate ASM treatment should raise the possibility. Unresponsive behaviour with movements mimicking a convulsion is seen in two‐thirds of people with FDS. Events mimicking atonic, absence, or focal non‐motor impaired awareness seizures are seen in one‐third.4 Semiological features may help distinguish FDS from epileptic seizures (Table 24.1). A fluctuating course, long duration, pelvic thrusting, asynchronous movements, side‐to‐side head or body movements, forced ictal eye closing, ictal crying, and memory recall favour FDS. Postictal confusion, seizures arising from sleep, and laboured breathing favour epileptic seizures.10 No single observation has sufficient sensitivity and specificity to differentiate FDS from epileptic seizures reliably. Eyewitness descriptions are often unreliable.11 High‐quality home videos can be useful in distinguishing FDS from epileptic seizures and other events, and complement video‐EEG recordings.12 The best videos show the person’s body and face before, during, and after the event. Accurate interpretation requires expertise. Certain features suggest FDS, such as variable movements between seizures, preserved awareness during a bilateral motor event, apart from frontal lobe seizures, and fluctuating intensity of symptoms. In contrast, stereotyped seizure patterns, rhythmic movements or progression matching known neuroanatomic pathways, and head or eye version followed by consistent motor progression, suggest epilepsy. A description of an individual’s subjective experience before and during seizures is important. There are often somatic and autonomic symptoms of anxiety, without the cognitive anxiety symptoms. This ‘panic without panic’ model is the basis of cognitive behavioural therapy for people with FDS. The presence of four or more of: palpitations, pounding heart, accelerated heart rate, sweating, shortness of breath, choking, chest pain, dizziness, unsteady, lightheaded, faintness, symptoms of derealisation, depersonalisation, fear of dying, paraesthesia, chills, or hot flushes favours FDS over epileptic seizures with 80% sensitivity and nearly 70% specificity.13 Open‐ended questions about warning symptoms before a seizure are of limited value and need to be supplemented by close‐ended questions about specific symptoms. Table 24.1 Ictal and postictal features distinguishing between epileptic seizures and FDS. Source: Adapted from Ref 10. * Frontal lobe seizures may present a diagnostic challenge. Seizures arising from the dorsolateral aspect may have activation of primary motor cortices, with forced eye version, clonic or tonic movements, head version, or aphasia. Seizures arising from the prefrontal cortex manifest as ‘hypermotor seizures’ with variable clinical manifestations, including bizarre gestures, laughing, shouting, and alternating limb movements such as peddling and thrashing of the extremities. Seizures originating from the cingulate gyrus can display complex stereotyped movements, such as kicking, grasping, or running, with or without vocalisations. Seizures arising from the supplementary sensorimotor area are characterised by sudden, brief, and asymmetric tonic posturing of one or more extremities with repetitive vocalisations and may cluster. Individuals may rapidly reorient after frontal lobe seizures and may have a postictal breathing pattern similar to that seen in FDS. ** Tongue biting, incontinence, and self‐injury, though more common in epileptic seizures, can occur in up to 30% of people with FDS. The medical history is also diagnostically relevant. Comorbid functional somatic syndromes such as fibromyalgia, chronic fatigue syndrome, chronic pain syndromes, tension headaches, and irritable bowel syndrome, or chronic intermittent illnesses including asthma, migraines, and gastro‐oesophageal reflux, can aid FDS diagnosis. The presence of at least one of these illnesses as a diagnostic test for FDS has a sensitivity of 66%, a specificity of 73%, and a negative predictive value of 62%.14 Comorbid psychiatric conditions have less diagnostic utility. One‐third of those with FDS had no comorbid psychiatric diagnoses. In the remainder, the most frequent diagnoses were: agoraphobia (45%), depression (31%), generalised anxiety (29%), post‐traumatic stress disorder (23%), and social phobia (20.4%).15 Symptoms of dissociation, specifically derealisation and depersonalisation, somatic and autonomic symptoms of panic before and during a seizure, and an individual’s comorbid medical conditions, can help to differentiate FDS from epileptic seizures. Open‐ended questions during history‐taking can show significant differences between epileptic seizures and FDS. Noting how questions are answered may be useful. Individuals with FDS tend to describe contextual or emotional impacts, while those with epilepsy often describe seizures as external events with more structured effort. These speech patterns are not diagnostic, but can aid in distinguishing between seizure types (Table 24.2). Table 24.2 Conversational features that may help distinguish Epileptic seizures and FDS ‐ This process involves asking individuals an open question such as ‘How can I help you?’ at the beginning of the consultation and then using interactional tools such as nodding, and reception markers (such as ‘hmm’) or silence to encourage the individual to continue their narrative. Source: Adapted from Ref 16.
CHAPTER 24
Functional Dissociative Seizures
EPIDEMIOLOGY
CLINICAL FEATURES OF FDS
VERBALLY REPORTED OR VIDEO‐OBSERVED SEMIOLOGY
SUBJECTIVE SYMPTOMS AND COMORBIDITIES OF FDS
Feature
Epileptic seizures
FDS
Duration
Often brief, <1–2 minutes
Often long, >2 minutes
Eyes
Usually open during event
Usually closed during event
Forced eye closure may be present
Consciousness during seizure
Complete loss of consciousness during convulsive seizure
Often incomplete loss of consciousness during convulsive seizure
Motor activity
Stereotyped
Synchronised
Gradually builds up
Head version and automatisms may occur
Variable (though FDS can be stereotyped, multiple seizure types may be present in one episode)
Asynchronous*, forward pelvic thrusting*, rolling side to side, opisthotonus
Waxes and wanes
Head version and automatisms rare
Ictal weeping
Rare
May occur
Vocalisation
Uncommon during convulsion (can occur at onset)
May occur during a convulsion
Prolonged ictal atonia
Rare
May occur
Incontinence and tongue biting
Common in convulsive seizures
Uncommon**
Autonomic signs
Cyanosis, tachycardia with major convulsion
Uncommon
Postictal symptoms
Confused, drowsy, amnestic for seizure
Deep and prolonged inspiratory and expiratory breathing after convulsive seizure.
Headache common
Quickly awaken and re‐orientated, may recall events during seizure*
Shallow, rapid respiration after convulsive seizure*
Headache rare (typically present before seizure as well)
COMMUNICATION STYLE
Favour Epileptic seizures
Individuals readily volunteer descriptions of seizure symptoms (including the last thing they remember and the next thing they remember, and seizure suppression attempts).
In response to enquiries, individual readily provides more detailed descriptions of their seizures.
The individual provides detailed seizure descriptions.
The individual focuses more on seizure symptoms than on their consequences or the situations in which they occurred.
The individual’s seizure descriptions are characterised by formulation effort (reformulation, hesitations, pauses).
Favour FDS
The interview is challenging.
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