Functional Movement Disorders

Introductions

A common presenting problem in neurology is the existence of disorders that present with neurological symptoms, but that are atypical for and incongruent with known neurologic disorders. Many different terms have been used to describe these disorders including “hysterical, conversion, psychogenic, dissociative, somatoform, nonorganic, and functional.” These terms reflect the concept that the symptoms are not based on identifiable organic disorders and that the symptoms and neurologic signs are incompatible with known anatomy and physiology. However, the historical distinction between “organic” and “psychogenic” may not be meaningful. The term “psychogenic” implies that the etiology disorder from the “mind.” It has been argued that “functional” should be the preferred term because is freer from assumptions of etiology and does not reinforce dualistic thinking. Indeed, there are data demonstrating abnormal function of neural circuits in patients with conversion disorder. The term “functional movement disorders” (FMD) is used in this chapter, but it should be understood that “psychogenic” and “functional” are still used interchangeably in the literature and in practice.

Historically, the concept of hysteria has been present in Western medicine for over 2000 years. Briquet in the 1850s and Charcot in the 1880s are generally recognized for their early work on disorders on the border zone between neurology and psychiatry and guiding them into modern medicine. The term conversion was first used by Breuer and Freud to describe the transformation of unresolved psychologic conflicts and unassimilated emotions into physical manifestations. Functional neurologic disorders fall under the broader heading of “Somatic Symptom and Related Disorders” in the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), “Conversion Disorder” is primary diagnosis, but the alternative name “Functional Neurological Symptom Disorder” is also included. Overall, there has been a shift in the literature to the use of “Functional Neurological Disorder” (FND), reflecting a greater emphasis on a biopsychosocial illness model with multiple factors contributing to symptom genesis. Diagnostic criteria for FND include the presence of symptoms affecting voluntary motor or sensory functions that suggest a neurological condition but that are judged to be caused by psychological factors. The symptoms cause impaired function, are not intentionally produced, and cannot be explained after a thorough medical evaluation. FND symptoms are characterized by having a voluntary quality, being modifiable by attention and distraction but perceived by the patient as involuntary. There must be “evidence of incompatibility between the symptom and recognized neurological or medical conditions,” which emphasizes the essential importance of the neurological examination. The diagnosis of FND functional neurologic disorder is typically made by a neurologist. The DSM-5 classification further recognizes that relevant psychological factors may not be demonstrable at the time of clinical presentation and diagnosis. Primary gain, secondary gain, or both may be present.

Epidemiology

Most studies of FND have focused on adult patients, and there are relatively fewer firm data on the prevalence of FND in children. The lack of data results from several factors including inconsistent use of terminology, lack of physician confidence in the diagnosis of FND, and a tendency to code diagnosis by predominant symptom. Furthermore, there is a lack of clinical or other criteria and assessment tools for FNDs. The first U.S. description of FND in children consisted of 98 cases. Despite continued study, few data exist to estimate the population prevalence of FND in children in the United States. Prevalence of FND among children has been estimated at one to four per 100,000. ^, In a study from a US urban hospital-based psychiatry consultation-liaison service, 11% of consultations resulted in a diagnosis of conversion disorder (FND). In a study from the U.K. and Ireland of 204 children and adolescents with conversion disorder, the most common symptoms were motor weakness and abnormal movements, but presentation with multiple symptoms was common. FND has been reported in children as young as 4 years, but most often presents during the peri-pubertal years. ^,

“Functional” disorders make up a significant percentage of referrals to neurologists. In a study of National Health Service referrals from primary care to adults neurology clinics in Scotland, 30% of patients were determined to have symptoms that were “not at all” or only “somewhat explained” by “organic disease.” FND is a relatively common reason for presentation to movement disorders clinics. Among adults, estimates vary from 2% to 10% of patients. ^, In one study, almost 20% of patients presenting to an emergency department with an acute movement disorder were determined to have a FMD. Common FMDs span the phenomenological spectrum and include dystonia, tremor, myoclonus, tics, hemiballismus, chorea, parkinsonism, and gait disorders. ^,

It has been estimated that 2%–5% of children presenting to movement disorders clinic have an FMD. Twelve of 52 children presenting to a busy pediatric movement disorders center in Australia with an acute-onset movement disorder were diagnoses with an FMD.

For FMDs in children, the average age of onset is 12–14 years, with a range of 7–18 years. ^{, , ,} No children under age 7 years were reported in those three series. FMDs affect girls more than boys in a 3:1 to 4:1 ratio. One report indicated a 1:1 ratio of boys to girls in children 12 years of age or younger.

The diagnoses of FND and FMD pertain to individuals. However, in rare instances, functional signs and symptoms appear to spread rapidly among members of a cohesive group. When this happens, it is referred to by many different names, such as “mass hysteria,” “mass psychogenic illness,” “sociogenic illness,” and others. Much less is known about the biological underpinnings and clinical features of mass psychogenic illness than is known about conversion disorder. Features of mass psychogenic illness are the occurrence of these symptoms in a cohesive group, the presence of increased anxiety, spread of symptoms via sight, sound, or oral communication (including social media), and high female:male ratio. There are many examples of mass psychogenic illness in history, most notably, perhaps, the Salem “witches.” More recently, an outbreak of a tic-like mass psychogenic illness occurred in Leroy, NY in which 19 teenage students at a single high school developed symptoms over a 5 month period of time. During the current Coronavirus Disease 2019 (COVID-19) pandemic, increased occurrence of functional neurologic disorders has been reported, and some aspects of this increase may be related to social media-related spread. Indeed, there have been several reports of young individuals, mostly adolescent girls, who have developed Tourette-like features after they started to watch and follow social media personality on TikTok, hence the term “TikTok tics.” ^,

Clinical Features of Functional Movement Disorders

In contrast to adults with FMDs, most of whom have multiple and complex movements, FMDs in children are typically mono-symptomatic, with a single movement disorder being present in a majority. Young children typically present after a minor injury, but older children are less likely to have a history of focal injury. In children, the dominant extremities are more likely to be involved than the nondominant extremities. ^{, ,} The typical course of conversion symptoms in children is for the symptoms to resolve within 3 months from the time of diagnosis. The great majority of children have complete resolution of symptoms, and recurrence appears to be rare. ^, The long-term outcome of FMDs has not been well studied in children but the prognosis is generally good in the majority of cases. ^, However, these reports from specialty clinics may reflect an ascertainment bias.

It is often possible to identify a specific precipitant for the conversion symptoms in children. In a study of 47 Israeli children with conversion disorder, a specific reason for the conversion was discovered in 40. Among children with FMD, antecedent history of physical or emotional stressors is common, being reported in 53%–80% of cases. ^{, , ,} Children with FMD commonly have coexisting impairment of mood, especially anxiety, depressed mood, or irritability, ^, and “perfectionistic” tendencies are common. ^, They may also have other medically unexplained symptoms associated with their movement disorder.

Pathophysiology

Multiple lines of evidence support the idea that FNDs are associated with altered brain function. These studies have been performed in adults, but it is reasonable to hypothesize that similar mechanisms are involved in children. One of the first studies to demonstrate this was a single photon emission computerized tomography (SPECT) study showing decreased regional cerebral blood flow in the thalamus and basal ganglia contralateral to functional sensorimotor deficits in adults. An important finding of that study was that the contralateral basal ganglia and thalamic hypoactivation resolved after recovery. In adult subjects with functional hemiparesis, cerebral blood flow responses in a motor imagery task were abnormally increased in the ventromedial prefrontal cortex and superior temporal cortex despite normal task performance. These studies and several other small studies using electroencephalography (EEG), structural MRI, functional MRI, PET, or SPECT have suggested that conversion disorders are associated with abnormal modulation of motor and sensory representations by affective or stress-related factors. ^,

Adult subjects with FMDs have impaired habituation to arousing stimuli and greater functional connectivity between amygdala and supplementary motor area (SMA). A subsequent study of 16 subjects with FMDs showed greater activity in limbic structures (right amygdala, left anterior insula, and bilateral posterior cingulate area) and decreased activity in the left SMA during a motor preparation task compared with controls. In addition, there is evidence for altered top-down regulation of motor activities, and increased activation of areas implicated in selfawareness, selfmonitoring, and active motor inhibition. ^, These data provide strong evidence for a neurobiological basis of conversion disorders; however, it remains unknown whether the abnormalities reflect causal mechanisms.