Functional Tic‐Like Behaviors: A Common Comorbidity in Patients with Tourette Syndrome

Abstract

Background

Comorbid functional tic‐like behaviors (FTB) have been described only rarely in patients with Tourette syndrome (TS).

Objectives

We present the first large sample of patients suffering from TS and FTB to raise awareness of this clinical presentation and to guide how to differentiate one from the other.

Methods

We analyzed clinical data of 71 patients (n = 27 [38.0%] female, mean age: 21.5, range: 11–55) with TS + FTB.

Results

In the majority of patients, FTB started abruptly on average 15 years after tic onset with “treatment‐resistant” complex movements and (“coprophenomena‐like”) vocalizations preceded by timely related psychological stressors. Psychological evaluation revealed evidence for internal conflicts (79%), emotional dysregulation (56%), and maintaining factors (70%). About one third of patients had a positive history for further medically unexplained symptoms. Compared to a large TS sample (n = 1032), patients with TS + FTB were more likely to be female, and presented significantly more common with “coprophenomena‐like” symptoms, atypical influential factors, atypical descriptions of premonitory sensations, and higher rates of comorbid obsessive‐compulsive disorder and “self‐injurious” behavior.

Conclusions

Based on our data it can be assumed that FTB is a common comorbidity in TS, similar to functional overlay in other movement disorders and epilepsy. Before classifying a patient as suffering from treatment‐resistant TS, FTB should be ruled out.

Tourette syndrome (TS) is characterized by the presence of motor and vocal tics. The majority of patients in addition suffer from psychiatric comorbidities, most commonly obsessive‐compulsive disorder (OCD) and attention‐deficit hyperactivity disorder (ADHD). ¹ , ² The phenotypic variability in TS widely ranges from patients with only mild and barely noticeable tics without any comorbid condition to patients with severe and complex tics with a variety of clinically relevant psychiatric comorbidities. Onset of tics is insidious and usually occurs in early childhood, on average at age 5 to 7 years. Tics have a typical waxing and waning course. Usually, worst tic severity is reached in adolescence at age 10 to 12 years. ² Besides spontaneous fluctuations and age dependency, tics are influenced by environmental factors, with stress being the main trigger, whereas relaxation and focused attention often result in tic amelioration. ³

An important differential diagnosis for neurological diseases is functional neurologic disorder (FND). ⁴ According to ICD‐11, ⁵ FND is characterized by symptoms that show internal inconsistency or incongruity. Similarly, in DSM‐5, ⁶ FND is defined by (1) the presence of one or more symptoms of altered voluntary motor or sensory function, (2) clinical findings of incompatibility between the symptoms and recognized neurological or medical conditions, (3) a clinical presentation that cannot be explained by another disorder, and (4) significant distress provoked by the symptoms. The prevalence of FND is estimated to be between 0.2% and 2% ⁷ but increases up to 15% ⁸ or even 30% ⁹ in a general neurological clinic. The two primary categories of FND include psychogenic nonepileptic seizures (PNES) and functional movement disorders (FMD).

The most frequent FMDs are tremor, dystonia, gait disorders, and parkinsonism, ⁷ whereas “functional tics” are considered a relatively rare presentation of FMD occurring even in specialized movement disorder clinics in only 4% to 5% of patients with FMDs. ¹⁰ , ¹¹ Therefore, until recently, only case reports including a small number of patients have been published. ¹² , ¹³ , ¹⁴ , ¹⁵ , ¹⁶ , ¹⁷ , ¹⁸ , ¹⁹ , ²⁰ , ²¹ , ²² Based on limited evidence, it has been postulated that “functional tics”—in contrast to “primary tics”—are characterized by lack of premonitory urges, ¹² , ¹⁷ inability to suppress symptoms, ¹⁷ , ¹⁹ isolated echophenomena, ¹⁹ , ²⁰ distribution of movements not following a rostro‐caudal pattern, ²¹ , ²³ , ²⁴ preceding traumatic events, ¹³ , ²³ adulthood onset, ¹⁸ , ²² , ²⁵ and absence of family history of tics. ¹⁷ , ¹⁹

However, in 2021, the situation changed dramatically, and a new type of “functional tic‐like behaviors” (FTB) was described characterized by rapid onset “tic/Tourette‐like” complex movements and vocalizations occurring mainly in young women presumably strongly influenced by corresponding presentations on social media. ²⁶ , ²⁷ , ²⁸ , ²⁹ , ³⁰ , ³¹ , ³² , ³³

To the best of our knowledge, so far only three case studies or series have been published describing patients diagnosed with TS and comorbid FTB. ¹² , ¹³ , ¹⁸ The first case, published in 1992, was an 18‐year‐old female with mild TS who suddenly developed complex movements such as slumping in a chair or to the floor with rhythmic tonic–clonic movements of all limbs that started at the age of 16. ¹² Two years later, two similar patients with TS were described, who developed FTB in the course of the disease. ¹³ The first case was a 9‐year‐old girl who developed bizarre movements such as jumping on the chair 2 years after tic onset that strongly depended on specific situations and most frequently occurred at school. After 5 days of hospitalization, symptoms suddenly resolved but reoccurred 10 days after discharge with thrashing the arms, legs, and trunk. The second case was a 16‐year‐old girl who developed complex movements described as “wild thrashing motions of all four limbs and of her trunk” 6 years after tic onset. After admission to a hospital, a history of sexual abuse became apparent. After this issue was addressed, “thrashing episodes” resolved while her tics persisted. In a recent study by Janik et al, a prevalence rate of FTB of 1.9% (n = 5, age range = 17–51 years, 1 female) was found in a cohort of 268 patients with primary tic disorders. In all patients, FTB started after tic onset and was characterized by complex movements with unchanged clinical pattern, inability to suppress symptoms, and absence of premonitory urges. In this study, in 2 of 5 patients, FTB remitted spontaneously.

This remarkably small number of patients with TS and comorbid FTB described so far is very surprising, because it is well known that in patients with movement disorders a “functional overlay” may occur. ³⁴ , ³⁵ , ³⁶ , ³⁷ For example, in Parkinson's disease (PD) a prevalence of FMD comorbidity of up to 8% has been reported, most commonly presenting with gait disturbances and tremor. ³⁶ Similarly, in epilepsy, comorbid PNES is the most common functional phenotype with a mean frequency of 12%. ³⁸ , ³⁹ , ⁴⁰ Following this background, one may speculate that such “functional overlay” is more common in patients with TS than previously thought.

The aim of this study is to raise awareness of comorbid FTB in patients with TS, to present clinical characteristics of the first large sample of patients with TS and FTB, and to guide how to differentiate one from another.

Patients and Methods

Between 2016 and 2021, we conducted a retrospective data analysis from patients seen in our specialized TS outpatient clinic between 2002 and 2021 to identify patients diagnosed with both TS and comorbid FTB. Diagnoses of TS and FND/FTB were established clinically in accordance with the Diagnostic and Statistical Manual of Mental Disorders (DSM) and were made in all cases by one of the authors (K.R.M.‐V.). In addition, a thorough retrospective evaluation of patients' records was performed by psychologists with expertise in tic disorders (C.F., A.P., E.J., and M.H.). It is worth mentioning that in this sample no patients with mass social media–induced sociogenic illness (MSMI) presenting with FTB have been included, ³¹ although in some of these patients an overlap with TS has also been reported. ³⁰ , ³¹

The diagnosis of TS is well established in our center and follows recommendations given by the European Society for the Study of TS ⁴¹ and the DSM‐5 criteria. ⁶ The diagnosis was based on patients' history; neuropsychiatric examination; symptom presentation; a detailed tic and TS‐specific history including symptom onset; number and kind of past and present movements and vocalizations; symptom fluctuations; influential factors; age dependency; premonitory urges; suppressibility; presence of echo‐, copro‐, and paliphenomena; impairment; coping strategies; recent and current treatments including efficacy and side effects; family history; and current and past psychiatric symptoms, including obsessive‐compulsive symptoms (OCS)/OCD, ADHD, depression, anxiety, sleeping problems, rage attacks, self‐injurious behavior (SIB), autism spectrum disorder (ASD), and substance use disorder.

Because during data collection no formal definition or rating scale for FTB was available, the diagnosis of FTB was based on patients' history, neuropsychiatric examination, symptom presentation, and overall clinical impression, including the following factors: (1) onset of so‐far‐unknown tic‐like symptoms that are very different from previous tics after a disease duration of many years (“different pattern”); (2) abrupt onset ²⁶ , ²⁷ , ²⁸ , ⁴² , ⁴³ , ⁴⁴ , ⁴⁵ ; (3) worsening or no response to treatment compared to recent response to anti‐tic therapies ¹⁸ , ²⁴ , ⁴⁶ ; (4) unusual or atypical descriptions of premonitory sensations, suppressibility, and influential factors with respect to increase, decrease, and remission of symptoms compared to descriptions related to preexisting tics ³⁰ , ³¹ , ⁴⁷ ; (5) occurrence of movements and vocalizations atypical for tics ¹⁹ , ²⁰ , ²¹ , ²⁴ , ²⁶ , ²⁷ , ²⁸ , ²⁹ , ³³ , ⁴² , ⁴⁴ , ⁴⁵ , ⁴⁶ , ⁴⁸ , ⁴⁹ , ⁵⁰ , ⁵¹ , ⁵² , ⁵³ , ⁵⁴ , ⁵⁵ , ⁵⁶ , ⁵⁷ ; (6) occurrence of SIB atypical of patients with TS ³⁰ , ⁴⁷ ; (7) secondary gain, for example, granting privileges at school or work ¹⁴ , ³⁰ , ⁴⁷ ; (8) atypical course or change in the course of symptoms in relation to the previous course of tics such as occurrence of “attacks,” temporarily spontaneous remission for hours or days, and strong influence of specific activities or presence of other people ¹⁹ , ²⁰ , ²¹ , ²⁶ , ²⁷ , ²⁸ , ²⁹ , ³⁰ , ³¹ , ³³ , ⁴² , ⁴⁴ , ⁴⁵ , ⁴⁶ , ⁴⁷ , ⁴⁸ , ⁵⁰ , ⁵¹ , ⁵² , ⁵⁴ , ⁵⁵ , ⁵⁶ , ⁵⁷ , ⁵⁸ , ⁵⁹ ; (9) distractibility during clinical examination ²⁸ , ⁵¹ ; and (10) self‐assessment of the patient who could differentiate between the twoconditions. ³⁰ , ⁴⁷

In patients with suspected FTB, in addition, we routinely asked the following questions: (1) factors precipitating the onset of FTB; (2) factors that lead to symptom exacerbation; (3) factors that lead to symptom amelioration or complete, but temporal remission; and (4) if those factors exist, patients were asked to name them. During clinical examination, it was checked whether distraction had any impact on FTB. FTBs were classified as simple or complex following the classification of tics of the Yale Global Tic Severity Scale (YGTSS). ⁶⁰ In line with previous descriptions related to FTB, ⁶¹ , ⁶² , ⁶³ we use the term “attack” that refers to prolonged paroxysmal cluster with repetitions of FTB that, in contrast to tics, last much longer, ranging from minutes to hours. Finally, each patient was evaluated according to the Shapiro TS Severity Scale (STSS), ⁶⁴ which is routinely administered to measure tic severity in our clinic. Evaluation of quality of life and impairment was based on clinical assessment and interview conducted by a tic disorders specialist (K.R.M.‐V.) and impairment domains listed in the YGTSS.

In addition, in all clinically diagnosed cases of TS + FTB, an independent retrospective data analysis was performed by an experienced psychologist, including the following factors: (1) type and onset of FTB; (2) time‐related psychological stressors; (3) course and factors influencing severity of FTB; (4) premonitory sensations and suppressibility of FTB; (5) maintaining factors for FTB; (6) presence of psychiatric comorbidities such as depression, OCS/OCD, ADHD, anxiety disorders, substance use disorders, and ASD; (7) a history of further medically unexplained symptoms, FMD and FND; and (8) type and response to treatment.

To distinguish coprophenomena that can be encountered in TS ⁶⁵ , ⁶⁶ , ⁶⁷ , ⁶⁸ from similar functional phenomena, here we use the term “coprophenomena‐like” symptoms to describe obscene words and gestures related to FTB. According to Ganos et al., ²⁰ patients with functional “coprolalia‐like” utterances mainly present to the clinic due to these complex vocalizations, in the almost‐complete absence of impairment provoked by other symptomatology. They often report premonitory sensations precipitating “coprophenomena‐like” symptoms very different and atypical compared to premonitory urges preceding tics in TS (eg, “a sudden energy pulse,” “generalized whole body pressure”). ²⁰ Moreover, coprophenomena in TS and “coprophenomena‐like” symptoms in FTB differ with respect to the content. Whereas coprolalia in TS is usually characterized by only a few, single, abrupt, short, noncontextualized words, ⁶⁵ , ⁶⁷ “coprolalia‐like” vocalizations in FTB often include a very rich repertoire of long phrases with an atypically high number of different words or combinations of words that—different from TS—can often be observed several times during a consultation. ²⁰ , ²⁷ , ²⁹ , ³⁰ , ³¹ , ⁴⁴ , ⁴⁷ , ⁶⁹ , ⁷⁰

Using the classification by Operationalized Psychodynamic Diagnosis (OPD‐2), ⁷¹ a psychological evaluation was performed by an experienced psychotherapist (A.P.) to detect evidence for the presence of internal conflicts and emotional dysregulation based on patient records using all information available, including long‐term follow‐up (mean: 5 years, range: 0–19 years). OPD mainly alludes to the fundaments of the psychodynamic thinking central notion to which is intrapsychic conflict. According to psychodynamic theory, intrapsychic conflict emerges when there is an opposition between incompatible or opposing wishes, impulses, needs, thoughts, or demands within one's own mind. There is an extensive background behind the use of psychodynamic theories in the treatment of FND. ⁷² , ⁷³ , ⁷⁴ , ⁷⁵ , ⁷⁶ , ⁷⁷ , ⁷⁸ , ⁷⁹ Early psychodynamic theories about the development of FND are related to psychoanalytical thinking of Sigmund Freud, ⁷⁸ but later on it was recognized as being far more complex. ⁷⁶ Importantly, many studies, including a number of randomized controlled studies, have confirmed the efficacy of psychodynamic psychotherapy in the treatment of FND. ⁷² , ⁷³ , ⁷⁴ , ⁷⁵ , ⁷⁶ , ⁷⁷ , ⁷⁹

Finally, we compared clinical data of this sample of patients with TS + FTB with a large cohort of 1032 patients with primary tic disorders seen in our specialized TS outpatient clinic between 1993 and 2013. ⁸⁰

Results

Baseline Characteristics and Onset of FTB

We identified 71 patients diagnosed with TS and comorbid FTB (27 women [38%], mean age = 21.5 years, range: 11–55 years). Before presentation in our center, FTB was not diagnosed in any patient.

In all patients (n = 71, 100%), FTB started after the onset of tics, on average 14.5 (±9.5 [standard deviation]) years after tic onset (mean age at tic onset = 6.3 ± 2.3 years, range: 2–21 vs. mean age at FTB onset = 20.8 ± 11.8 years, range: 5–52, P = 0.05). Altogether 61 patients (86%) described onset of FTB as sudden worsening of symptoms after a long and relatively stable course of the disease. More than half of patients (n = 38, 54%) reported an abrupt onset of FTB and were—in contrast to tic onset—able to precisely indicate the date when FTB started. After the diagnosis of comorbid FTB had been made, 34 patients (48%) stated feeling able to differentiate tics from FTB.

Clinical Presentation of FTB

Movements

The most common presentation of motor FTB was complex movements (n = 57, 80%), which were mainly located at the upper extremities (most frequently throwing and breaking of objects, self‐hitting, hitting others, and obscene gestures atypical of copropraxia in TS), often involving several body parts or even the whole body (eg, lying on the floor), and thus did not follow the typical rostro‐caudal distribution of tics. SIB atypical of TS occurred in 39 patients (55%), with self‐hitting being the most common type.

Vocalizations

Similarly, the most frequent presentation of vocal FTB were complex vocalizations (n = 28, 39%, eg, obscene words and phrases atypical of coprolalia in TS, screaming provoked by the presence of a particular person such as family members, animal sounds, and repetitive shouting of phrases).

“Coprophenomena‐Like” Symptoms

Overall, FTB with obscene words and gestures (“coprophenomena‐like” symptoms) were present in 31 patients (44%), with functional obscene words in 27 (38%) and functional obscene gestures in 7 (10%) patients. The repertoire of functional obscene words was often extremely abundant, including up to 10 to 15 different words/phrases.

“Attacks” of FTB

Thirty‐three patients (46%) reported that vocal and motor FTBs typically occur in clusters (“attacks”), with repetitions up to 40 times and symptom persistence for many hours or even the whole day.

Tic Severity and Overall Impairment

According to retrospective evaluation based on clinical judgment and severity of primary tics according to STSS, tic severity was assessed as mild in 45 (63%), mild to moderate in 3 (4%), moderate in 5 (7%), moderate to severe in 4 (6%), and severe in 4 patients (6%). In 10 patients (14%), retrospective evaluation was not possible. However, based on patients' reports, 57 patients (80%) felt significantly impaired by their symptoms (including tics and FTB) influencing functional domains such as school, work, and everyday life (eg, driving a car, walking, and cleaning), and a few patients reported being even unable to walk without assistance or to lie independently. In 17 patients (24%), retrospective assessment of overall impairment was not possible.

Influential Factors on FTB

Forty‐four patients (62%) reported a complete cessation of FTB in particular situations. Thirty‐four patients (49%) reported a strong influence on FTB by the presence of particular family members, with an increase in 24 (34%) and a decrease in 11 patients (15%) (multiple answers possible). Furthermore, FTBs were reported to be influenced by the following factors: occurrence in only particular situations (eg, during “bioenergetic treatment” or after a panic attack, n = 53), in specific places (eg, in the train or at home, n = 21), during specific activities (eg, during everyday activities like cleaning or only when writing with a pen, n = 14), or in particular positions (eg, when sitting, n = 2). Improvement of FTB was reported most often when being relaxed (n = 17), when concentrating on one specific task (n = 9), during sleep (n = 5), and in the presence of a particular person (eg, a family member) (n = 3). In 51 patients (72%) symptoms markedly improved or completely remitted during clinical examination in our center.

Premonitory Sensations and Suppressibility of FTB

Nearly half of patients (n = 35, 49%) reported premonitory sensations preceding FTB. However, descriptions largely differed from those given for tics—usually described as brief sensations of tension or itchiness especially in the region of the body where later tics occur ⁸¹ —with respect to (1) duration, (2) character, and/or (3) localization. For example, premonitory sensations were described as involving the whole body or body regions not at all associated with the localization of FTB, as lasting several minutes, or with very different feelings compared to premonitory urges preceding tics in TS such as an “electric shock” or a “vibration of the tongue.”

Overall, 55 patients (72%) reported being able to suppress their symptoms voluntarily. However, retrospective data analysis did not allow to differentiate between suppressibility of tics and FTB.

Psychiatric Comorbidities

On average, patients suffered from 2.3 further psychiatric comorbidities, most frequently OCS (n = 41, 58%), ADHD (n = 26, 37%), depression (n = 23, 32%), anxiety (n = 19, 27%), OCD (n = 17, 24%), and ASD (n = 2, 3%). Remarkably, 24 patients (34%) had a positive history for further medically unexplained symptoms, including fluctuating inability to walk or to speak, visual problems, paralysis, PNES, sudden temporary attacks of tremor or spasms, abdominal pain, dyspnea, and hyperventilation.

Treatment

On average, patients had received 4.9 (range: 0–14, standard deviation: 3.05) different pharmacological agents for the treatment of primary tics, FTB (misdiagnosed as tics), and/or comorbidities. After use of anti‐tic medications, 20 patients (28%) reported unusual or even unknown side effects such as inability to walk, extreme hypersensitivity to light, paralysis, dyspnea, sudden attacks of screaming, anger attack or sudden anxiety. At the time of referral to our center, 33 (47%) patients had been classified as “treatment‐resistant” TS, and 7 of 71 patients (10%) had received surgical therapy with deep brain stimulation (DBS) to improve otherwise “treatment‐resistant tics.”

Psychological Evaluation

Psychological evaluation revealed evidence for unconscious intrapsychic conflicts in 56 patients (79%) and for emotional dysregulation in 39 patients (56%). Altogether 38 patients (54%) reported having experienced time‐related psychological stressors preceding the onset of FTB such as family conflicts, overworking, feeling of being overwhelmed with duties at school, illness of family members, and parents' divorce. In 50 patients (70%) disease‐reinforcing factors for FTB were detected, such as relief from everyday household duties or demanding tasks at work, implementation of a driving service to workplace, or receipt of support for specific tasks.

Comparison between Patients with TS + FTB and a Large Independent TS Sample

For some of our data, we were able to compare the results directly with data obtained from our recently published large, independent, single‐center TS sample (n = 1032). ⁸⁰ Whereas we found no differences with respect to patients' mean age and mean age at onset of primary tics, the TS + FTB group consisted of significantly more women compared to the TS sample (38% vs. 23%, P = 0.003). In addition, in the TS + FTB group “coprophenomena‐like” symptoms (compared to coprophenomena) were significantly more common (43% vs. 28%, P = 0.005) as well as comorbid OCD (23% vs. 10%, P < 0.001), and SIB (56% vs. 30%, P = 0.009). The comorbidity score (equal to the number of comorbidities) in the TS sample (2.67) was slightly but nonsignificantly higher compared to the TS + FTB group (2.28) (P = 0.4). Although in the TS + FTB sample our data did not allow to differentiate between suppressibility of tics and FTB, overall suppressibility of symptoms was reported to a lesser extent by the TS + FTB group compared to the TS group (72% vs. 85%, P = 0.07). Table 1 provides more details comparing both samples.

TABLE 1.

Comparison of patients with TS + FTB (n = 71) with an independent sample of patients with primary tic disorders (TS, n = 1032)

	TS + FTB	TS	P
Female, n (%)	27 (38%)	236 (23%)	0.003
Age (mean, SD)	21.5 (12.7)	18.98 (12.97)	0.1
Tic onset (mean age, SD)	6.3 (2.3)	7.17 (3.72)	0.06
Number of psychiatric comorbidities	2.3 (1.32)	2.67 (1.57)	0.4
OCD, n (%)	16 (23%)	103 (10%)	0.0009
OCS, n (%)	41 (58%)	637 (67%)	0.5
ADHD, n (%)	26 (37%)	463 (44.9%)	0.18
Anxiety, n (%)	19 (27%)	323 (31%)	0.4
Depression, n (%)	23 (32%)	236 (23%)	0.07
SIB, n (%)	40 (56.3%)	405 (39.4%)	0.009
Coprophenomena/“coprophenomena‐like” symptoms, n (%)	31 (43%)	289 (28%)	0.005

Abbreviations: TS, Tourette syndrome; FTB, functional tic‐like behaviors; SD, standard deviation; OCD, obsessive‐compulsive disorder; OCS, obsessive‐compulsive symptoms; ADHD, attention‐deficit hyperactivity disorder; SIB, self‐injurious behavior.

Discussion

This is the first study describing a large sample of patients with TS, who suffer from comorbid FTB. In line with available case studies, ¹² , ¹³ , ¹⁸ FTB typically started suddenly (often described as a “tic attack”) several years after tic onset. Although FTB presented with a variety of complex movements and vocalizations and, thus, largely differs from previous phenomenology and course of tics, FTB was misinterpreted as a deterioration of primary tics. Therefore, nearly half of patients were classified as “treatment‐resistant” TS, and 7 (10%) had even received DBS for this indication. Interestingly, about half of patients felt able to differentiate between tics and FTB after having been informed about the diagnosis of comorbid FTB.

Compared to patients with TS (without FTB), we were able to identify several differences in patients with TS + FTB, including a greater proportion of women, significantly more “coprophenomena‐like” symptoms and a higher rate of comorbid OCD and SIB. Remarkably, about one third of patients with comorbid FTB had a positive history for further medically unexplained symptoms with a wide spectrum of symptoms. In line with recent descriptions in patients with FND/FMD, ⁸² , ⁸³ patients with TS + FTB often reported atypical or even unknown side effects after treatment with anti‐tic medications.

Until recently, co‐occurrence of TS and FTB was regarded a rare clinical presentation resulting in only three publications comprising 8 patients. ¹² , ¹³ , ¹⁸ Moreover, publications regarding FTB were also very limited until 2016 ¹⁵ , ¹⁷ , ¹⁸ , ¹⁹ , ²⁰ , ²¹ , ²² (for summary see Table 2).

TABLE 2.

Studies reporting on FTB (presented in chronological order)

Study	Year of publication	Study population	Number of participants (all/patients with FTB)	Term used to describe abnormal movements/vocalizations	Mean age	Mean age of FTB onset	Gender
Kurlan et al. 12	1992	TS + FTB	1/1	Pseudo‐tics	18	16	1M
Dooley et al. 13	1994	TS + FTB	2/2	Pseudo‐tics	12.5	12.5	2F
Mejia and Jankovic 14	2005	Secondary tics	155/16	Psychogenic tics	40.5	NR	NR
Ahmed et al. 15	2008	FMD	34/13	Abnormal body movements	10.1	NR	13 men
van der Salm et al. 16	2013	FMD	60/5	Tics	NR	NR	NR
Baizabal‐Carvallo and Jankovic 17	2014	FTB	9/9	Psychogenic movement disorders resembling tics/psychogenic tics	36.3	34.1	4M, 5F
Janik et al. 18	2014	TS + FTB	5/5	Psychogenic tics	34.0	34.0	4M, 1F
Ganos et al. 19	2014	FTB	1/1	Functional tics	18	16	1F
Demartini et al. 21	2015	FTB	11/11	Functional (psychogenic) tics	43.5	37.2	8M, 3F
Vale et al. 22	2016	FTB	1/1	Late‐onset psychogenic chronic phonic tics	67	59	1F
Ganos et al. 20	2016	Functional coprolalia	13/13	Tic‐like vocalizations	21.8	19.5	9M, 4F
Robinson and Hedderly 62	2016	FTB	12/12	Tic attacks	11.3	11	9M, 3F
Versace et al. 25	2019	FTB	1/1	Adult onset TS	48	47	1M
Vial et al. 27	2019	FTB	2/2	Functional (psychogenic) movements	41	39.5	1M, 1F

Note: In this table no studies on MSMI‐FTB are included.

Abbreviations: FTB, functional tic‐like behaviors; TS, Tourette syndrome; M, male; F, female; NR, not reported; FMD, functional movement disorders; MSMI‐FTB, mass social media‐induced sociogenic illness.

Since 2019, this situation has changed as a surge in FTB in different centers has been detected. Increased prevalence of FTB has been attributed to different factors such as the influence of social media ³⁰ , ³¹ , ⁶⁹ , ⁷⁰ , ⁸⁴ as well as isolation and overall psychological stress during the COVID‐19 pandemic, ⁴³ , ⁸⁵ resulting in increased anxiety and depression. ²⁹ , ⁴² Other factors such as exposure to traumatic events in the past ³⁰ and genetic predisposition ⁴² may also influence the occurrence of FTB but do not explain the outbreak since 2019. Different terms have been proposed to name this new phenomenon, including atypical tics, ⁸⁶ functional tic‐like phenomena, ⁵¹ mass social media‐induced illness presenting with Tourette‐like behavior (MSMI‐FTB), ³⁰ , ³¹ rapid onset functional tic‐like disorder or behaviors, ²⁶ , ²⁷ , ²⁸ , ²⁹ pandemic tic‐like behaviors, ⁸⁷ or simply functional tics. ³⁰ , ³¹ , ⁵⁷ In recently published articles by our group, ³⁰ , ³¹ we introduced the term MSMI‐FTB to emphasize the impact of and spread via social media.

Recent outbreak of (MSMI‐)FTB enabled for the first time careful characterization of FTB in larger samples demonstrating that (MSMI‐)FTB is more common in women, mainly presenting with complex movements involving arms and trunk, and a large number of complex vocalizations with obscene, socially inappropriate, or offensive words, sentences, and behaviors. ²⁶ , ²⁷ , ²⁹ , ³⁰ , ³² , ³³ , ⁴³ , ⁵⁷ , ⁶⁹ , ⁷⁰ , ⁸⁸ Remarkably, in our own sample of patients with MSMI‐FTB (n = 32), half of patients suffered in addition from TS, suggesting a “functional overlay” too. ³⁰

Our classification of patients as suffering from TS + FTB seems justified for several reasons. First, mean age at tic onset was 6 years and thus comparable to typical onset of tics in TS, ² whereas FTB started on average at age 21 years, which is in line with several previous reports of adult onset of FTB. ¹⁷ , ¹⁸ , ²¹ , ²² , ²⁵ , ⁸⁹ , ⁹⁰ Interestingly, in our independent sample with MSMI‐FTB, ³⁰ FTB started at nearly the same age (n = 32, mean age: 19 years). Second, symptoms classified as FTB mainly started suddenly, which is in line with other descriptions of FTB ¹⁹ , ²⁰ , ²¹ , ²⁴ and MSMI‐FTB, ²⁶ , ²⁹ , ³⁰ , ³³ , ⁴³ , ⁷⁰ but also other types of FND/FMD. ⁷ , ⁹¹ , ⁹² Third, although the majority of patients with TS + FTB were men (62.0%), the proportion of women was significantly higher than in typical TS samples. ⁸⁰ Female gender is a well‐known risk factor for the development of FND. ⁹³ , ⁹⁴ Similarly, a female preponderance has been described in (MSMI‐)FTB ³⁰ , ³¹ , ⁴⁷ and FTB samples of more multifactorial origin. ²⁶ , ²⁷ , ²⁹ , ³³ , ⁴⁴ , ⁵⁴ , ⁵⁵ , ⁵⁷ Similarly to our sample, studies describing (MSMI‐)FTB included patients with predominantly complex movements, vocalizations, ¹⁷ , ¹⁸ , ¹⁹ , ²⁰ , ²¹ , ²⁴ and SIB (mainly self‐hitting). In our study, SIB occurred not only significantly more frequent in patients with TS + FTB compared to our independent TS sample (56% vs. 39%) ⁸⁰ but also with similar high frequency compared to our MSMI‐FTB sample (56% vs. 47%). ³⁰ Several of our patients suffered from complex vocalizations, with a large number of obscene words and phrases, screaming, and repetitive shouting of phrases very similar to recent reports in patients with (MSMI‐)FTB. ³⁰ Fifth, in line with previous descriptions of (MSMI‐)FTB, ⁶¹ , ⁶² , ⁶³ nearly half of our patients reported the occurrence of “tic attacks.” Sixth, similar to our patients with TS + FTB, in other FTB samples ²¹ influential factors were described very different from those known to alter primary tics. Completely different from patients with TS, but in line with samples with (MSMI)‐FTB, ²⁶ , ³⁰ , ⁴⁴ a substantial number of patients with TS + FTB reported complete remission of symptoms. Seventh, although tic severity was classified as mild to moderate in 74% of our patients, patients had received on average five different anti‐tic medications. In accordance with the fact that “treatment refractoriness” is regarded a hallmark in FMD/FTB, ¹¹ , ¹⁷ , ²⁰ nearly half of our patients had been classified as “treatment‐resistant,” whereas in TS treatment refractoriness is found in about 30% of patients. ⁹⁵ , ⁹⁶ , ⁹⁷ Eighth, in line with recent findings in MSMI‐FTB, ³⁰ he presence of internal conflicts and emotion dysregulation in  patients with TSpredispose to occurrence of FTB. Similar to other studies in FND/FMD/FTB, ⁹⁸ , ⁹⁹ , ¹⁰⁰ in a large number of patients we identified time‐related psychological factors that preceded the onset of FTB.

Our findings are in large agreement with the recently published clinical criteria for the diagnosis of FTB by international tic experts. ⁴⁵ In this consensus statement it has been proposed that the diagnosis of FTB is clinically definite, when the following three major criteria are fulfilled: age at first symptom onset of 12 years or older, rapid onset and evolution of symptoms, and typical phenomenology that includes at least four of the following nine features: (1) multiple FTBs with larger number of complex than simple FTBs; (2) the same FTB is reproduced; (3) motor FTBs include complex arm and hand movements (chest/head banging, tapping, hitting others, throwing objects, offensive gestures, drop attacks, or freezing); (4) lack of rostro‐caudal distribution; (5) vocal FTBs include many words and statements, including context‐dependent ones; (6) FTBs are similar to the ones displayed by social media influencers, friends, and family members; (7) patients display large variations in symptoms that could resolve within the course of the day; (8) FTBs change rapidly on a daily basis; and (9) there is an increase in FTB during clinical examination. Thus, although in our sample not all of these criteria could be evaluated retrospectively, in our opinion, numerous findings indicate that classification of symptoms as FTB instead of tics is justified.

Recent findings in patients with (MSMI‐)FTB also shed new light on patients who so far have been diagnosed with “atypical,” “adult‐onset,” and “treatment‐resistant” TS. ²² , ⁸⁹ , ¹⁰¹ , ¹⁰² , ¹⁰³ , ¹⁰⁴ Thus far, only 26 patients diagnosed with “adult‐onset” TS have been reported in the literature. It can be speculated that at least some of these patients may suffer, instead of or in addition to TS), from FTB. This assumption is further supported by the fact that most of these patients—similar to patients with FTB—are described as “treatment resistant,” and OCD is the most common comorbidity. ⁸⁹

A remarkably high number (10%) of our patients with TS + FTB had received DBS to improve otherwise “treatment‐resistant tics.” Based on this finding—and in line with recent data in patients with TS ¹⁰⁵ and other movement disorders such as PD and dystonia ¹⁰⁶ —it can be speculated that data outcome after DBS may be complicated by FMD. Furthermore, in patients with presumed otherwise treatment‐resistant tics, FTB should be excluded, before taking DBS into account.

The following limitations of our study must be addressed: (1) data were analyzed retrospectively; (2) data analysis may be biased by missing data; and (3) differentiation between tics and FTB was based only on clinical judgment, because at the time of data analysis no diagnostic criteria for FTB had been published; however, patients' perception and retrospective assessment by trained psychologists were considered too. In any case, evaluation was performed by an experienced TS expert (K.R.M.‐V.), but judgment was not based on group consensus; and (4) severity of both tics, FTB, and impairment was based merely on clinical evaluation because in clinical routine practice we use only the STSS.

To summarize, our data suggested that FTB is a common comorbidity in patients with TS similar to the well‐known concept of functional overlay in other movement disorders and epilepsy. Because we were able to identify several factors that are regarded typical of FTB/FMD such as abrupt onset, onset in early adulthood, larger‐than‐excepted female proportion, mainly complex movements and vocalizations, atypical influential factors and premonitory sensations, treatment refractoriness, partly spontaneous remission, and high incidence of further medically unexplained symptoms, we are convinced that symptoms were not mistaken as FTB instead of primary tics. The concept of comorbid FTB is corroborated by a remarkable overlap with recent reports in (MSMI‐)FTB. Because several of our patients had received high numbers of different medications, were classified as “treatment‐resistant TS,” or had received DBS, clinicians should be aware that comorbid FTB is much more common in patients with TS than previously believed.

Author Roles

(1) Research project: A. Conception, B. Organization, C. Execution; (2) Statistical analysis: A. Design, B. Execution, C. Review and critique; (3) Manuscript: A. Writing of the first draft, B. Review and critique.

K.R.M.‐V.: 1A, 1B, 1C, 3A, 3B

E.J.: 1C, 2A, 2B, 2C, 3B

A.P.: 1C, 2B, 3B

C.F.: 1B, 1C, 3B

N.S.: 2C, 3A, 3B

M.H.: 1C, 2A, 2B, 2C, 3B

Disclosures

Ethical Compliance Statement: The study was reviewed and approved by Local Ethics Committee at Hannover Medical School (no. 8995_BO_S_2020). Written informed consent to participate in this study was provided by the participants and their legal guardian/next of kin. We confirm that we have read the Journal's position on issues involved in ethical publication and affirm that this work is consistent with those guidelines.

Funding Sources and Conflict of Interest:

This study was not funded by any external sources.

Financial Disclosures for the Previous 12 Months: K.R.M.‐V. has received financial or material research support from the European Union (FP7‐HEALTH‐2011 no.: 278367, FP7‐PEOPLE‐2012‐ITN no.: 316978), DFG: GZ MU 1527/3‐1 and GZ MU 1527/3‐2, BMBF: 01KG1421, National Institute of Mental Health (NIMH), Tourette Gesellschaft Deutschland e.V., Else‐Kröner‐Fresenius‐Stiftung, GW Pharmaceuticals, Almirall Hermal GmbH, Abide Therapeutics, and Therapix Biosiences. She has received consultant's and other honoraria from Abide Therapeutics, adjupharm, Alexion, AMP Alternative Medical Products GmbH, Ingelheim International GmbH, Bionorica Ethics GmbH, CannaMedical Pharma GmbH, Canopy Grouth, Columbia Care, CTC Communications Corp., Demecan, Enua Pharma, Ethypharm GmbH, Eurox Group, Global Praxis Group Limited, Lundbeck, MCI Germany, Neuraxpharm, Sanity Group, Stadapharm GmbH, Synendos Therapeutics AG, Syqe, Tilray, and Zambon. She is an advisory/scientific board member for Alexion, Branchenverband Cannabiswirtschaft e.V. (BvCW), CannaMedical Pharma GmbH, Bionorica Ethics GmbH, CannaXan GmbH, Canopy Growth, Columbia Care, Ethypharm GmbH, IMC Germany, Leafly Deutschland GmbH, Neuraxpharm, Sanity Group, Stadapharm GmbH, Synendos Therapeutics AG, Syqe Medical Ltd., Therapix Biosciences Ltd., Tilray, von Mende Marketing GmbH, Wayland Group, and Zambon.

She has received speaker's fees from Aphria Deutschland GmbH, Almirall, Bedrocan, Camurus, CEREBRO SPAIN BIDCO S.L., Cogitando GmbH, Emalex, Eurox Deutschland GmbH, Ever Pharma GmbH, GROW, Hessische Landesstelle für Suchtfragen e.V. (HLS), LIO Pharmaceuticals GmbH, Medizinischer Dienst Westfalen Lippe, Meinhardt Congress GmbH, PR Berater, Spectrum Therapeutics GmbH, Takeda GmbH, Tilray, and Wayland Group. She has received royalties from Deutsches Ärzteblatt, Der Neurologie und Psychiater, Elsevier, Medizinisch Wissenschaftliche Verlagsgesellschaft Berlin, and Kohlhammer. She served as a guest editor for Frontiers in Neurology on the research topic “The neurobiology and genetics of Gilles de la Tourette syndrome: new avenues through large‐scale collaborative projects,” is an associate editor for Cannabis and Cannabinoid Research, is an editorial board member of Medical Cannabis and Cannabinoids and MDPI‐Reports, and is a scientific board member of Zeitschrift für Allgemeinmedizin. N.S. received financial research support from the Polish Ministry of Education, Polish Neurological Society, European Stroke Organization, Fundacja na Rzecz Nauki Polskiej, American Academy of Neurology, American Brain Foundation, and Tourette Association of America. Other authors report no conflicts of interest.