Tics are sudden, rapid, non-rhythmic movements or vocalizations, which occur in 1 in 5 school-aged children (14). Chronic Tic Disorders (CTD), including Tourette Syndrome (TS), are developmental neurobiological disorders characterized by multiple motor and/or vocal tics for at least 1 year. Co-occurring conditions such as attention deficit hyperactivity disorder (ADHD), obsessive-compulsive disorder (OCD), and anxiety occur in 90% of individuals with CTD (15–19).

Tics begin gradually in early childhood, fluctuate, and change over time (16, 18, 20). There is a male predominance of tics, 4:1 male to female ratio, which diminishes in adulthood (18, 20, 21). For the vast majority of individuals with CTD, tics peak in the peri-pubertal period and improve through adolescence (20).

Tics often begin as simple motor tics and progress over time in a rostro-caudal distribution (22). Tics are preceded by a premonitory urge, often localized to the affected body region (23). Premonitory urges are an itch, tension, need or unpleasant sensation that builds with voluntary suppression and is relieved by completing the tic (24, 25). Recognition of premonitory urges tends to occur between 8 and 10 years old, although is reported by the majority of individuals with CTD (24, 26, 27).

Whether the phenotype of TS is different in affected females is poorly understood. There are conflicting reports on the sex-differences of comorbidity prevalence (16, 18, 21, 28–32). Some studies have reported TS-affected females have later onset of tics (16, 33, 34), later peak of tic severity (29, 34), motor tic severity (32, 33), and lower likelihood of tic remission; however, others have shown conflicting results or no significant sex-differences in these factors (18, 28, 32, 33, 35).

Complex tics, including coprophenomena, echophenomena and self-injurious behaviors (SIB) are often misunderstood by the public (36). Risk of coprophenomena such as obscene gestures (copropraxia) or words (coprolalia) increases with age and co-occurring conditions. Coprolalia is three times more common than copropraxia, with a lifetime prevalence of 8–18.5 and 5.7% respectively and often occurs within 5 years of tic onset (18, 37–39).

Echophenomena refers to the repetition of other's actions (echopraxia) or sounds/words (echolalia). In the original publications from Georges Gilles de la Tourette, the persistence of echophenomena beyond normal expected childhood development was essential for the diagnosis of TS (40). Given the heterogeneity of CTD, echophenomena are now considered a distinctive feature rather than a requirement for diagnosis (41), with an estimated lifetime prevalence 43–56% (42, 43).

SIB can occur in 4–53% of individuals with CTD (18, 44, 45). Estimates vary depending on the definition of SIB, which can range from skin picking or scratching, biting, head banging, or self-hitting, to more severe symptoms such as self-cutting, body deformation, or self-mutilation (46). Rarely, individuals affected with TS can have life-threating symptoms (44, 47).

Functional movement disorders (FMD) are a common presentation in neurology clinics (48). Many different terms have described these disorders including conversion disorder, psychogenic, nonorganic, medically unexplained, and hysteria (49, 50). Although psychogenic and functional are often use interchangeably, functional is the preferred terminology. Functional is freer of stigma and more reflective of the current understanding of the pathophysiology on FMD, which suggest a neurobiological basis of these disorders (12, 49, 51, 52). A combination of predisposing, precipitating, and perpetuating factors play a role in development of FMD. Psychosocial stressors, low socioeconomic status, psychiatric comorbidities, female gender, and adverse experiences may increase risk of FMD. It is hypothesized that both epigenetic and genetic factors may contribute to FMD, but current evidence is limited (53). Additionally, brain maladaptation and plasticity may serve as perpetuating factors for FMD (12, 49, 54–56). The Diagnostic and Statistical Manual for Mental Disorders–Fifth Edition (DSM-5) adopted new emphasis on diagnosing based on positive features and removed the necessity of a precipitating stressor as with many patients none are found (57).

The true prevalence of FMD is hard to discern given diagnostic uncertainty, inconsistent terminology, and variability of utilized billing codes (48, 58). Diagnosis relies on inconsistencies and incongruences with known movement disorders. Across all ages, tremor, dystonia and gait disorders are the most common phenomenology of FMD, and FT were rarely reported (13, 59–61).

Estimates of pediatric FT prevalence vary from 0 to 17% (61–64). The rarity of FT may be attributed to the challenge in distinguishing FT from CTD. Many of the positive features used to diagnose FMDs such as distractibility, suggestibility, and fluctuating course are common amongst CTD. Clinical expertise and prior case studies suggest there are some key distinguishing features (10, 12, 65–68). While most individuals with pre-existing FMD reported no change in symptoms with the COVID-19 pandemic, there has been a dramatic increase in new FT (7–11, 69, 70).

FT have key clinical characteristics that distinguish them from CTD. FT present in adolescents often without a prior history of tics. There is a 3:1 to 9:1 female predominance in FTs. This is in contrast to CTD, which are heavily male dominant (13, 20, 59, 61, 71). Common features include abrupt onset followed by a static or progressive course, high-degree of suggestibility, and complete distractibility. FT lack suppressibility, build up with voluntary suppression, or relief upon completion of the tics (65, 66). Although the presence or absence of a premonitory urge is less definitive, when present in FT it is less often localized to the area of the tic-like behavior (11, 72, 73).

Unlike CTD, FT include complex and large amplitude movements at onset (11). Complex tics such as pali-, echo-, and copro-phenomena are less common in FT and are often more complex, variable, longer in duration, or context-dependent (72, 74, 75). The progression of FT tends to disregard the expected rostro-caudal distribution seen in CTD (66, 76). Frequently other functional neurological or somatic symptoms are present (65, 66).

Some studies note a lack of family history of tics in individuals with FT; however, an important caveat is that there may be a heredity component to FMD (51, 65, 77, 78). There is also potential for false-negative family history, as some may not recognize they had tics previously. Alternatively, a false-positive family history can occur given the prevalence of CTD. Additionally, while a precipitating event can occur, it is important to note stressors and adverse experiences are risk factors rather than requirements for diagnosis (13, 50, 64, 65). Treatment resistance to typical tic medications may also occur (65, 66).

Mass Functional Illness (MFI), also known as mass psychogenic illness, mass hysteria, mass conversion disorder, or mass sociogenic illness, is “the rapid spread of illness signs and symptoms affecting members of a cohesive group” (79). MFI has been described for many centuries and occurs in varied cultures, ethnic groups, and religious settings (79, 80).

Historically, there are two categories of MFI: anxiety or motor phenomena. Anxiety MFI is characterized by transient, benign symptoms typically resolving within 24 h when there is a sudden, extreme stress or perceived threat in a cohesive group (81). Symptoms can include dizziness, headache, fatigue or hyperventilation. Motor MFI typically presents with gradual onset of motor symptoms including hyper- or hypo-kinetic movements, gait abnormalities and speech difficulties. Symptoms evolve over weeks to months and gradually remit.

Over the past two decades there has been increased motor presentations. There are many examples throughout recent history of MFI including outbreaks of non-epileptic spells, weakness, twitching, and gait abnormalities often in adolescent females (82–86)³.

Perhaps one of the most notable relevant examples was the outbreak of sudden onset of tic-like behaviors in August 2011 through January 2012 at Le Roy High School in Western New York State (68). The 19 affected individuals (18 females, 1 male), who did not belong to the same social group initially, formed a new social group based on their common disorder. Similarly, there were two outbreaks of hiccups and vocal tic-like behaviors of over a dozen students in two nearby Massachusetts high schools in November 2012 and January 2013 (87).

Like FMD, females have been reported to have a higher propensity to MFI (88, 89). A recent meta-analysis of gender differences showed 2.4:1 female predominance of MFI in children and adolescent (90). These outbreaks become the target of substantial media attention as well as thorough investigations into exposures, recent vaccinations, or environmental triggers (90–93).

Presence of movement disorders on social media is not novel. Review of videos on YouTube in 2011 by movement disorder specialists revealed 66% of movement-related videos were FMD (94). Interestingly enough, 18% (5,450/30,095) of movement-related videos reviewed were categorized as tic-related content.

Historically, MFI has been limited to a cohesive group; however, in the modern-day era, social media breaks the geographic barriers that typically confine such symptoms. Bartholomew was one of the first to propose the role of social media in MFI (81, 87). YouTube and Facebook were implicated in the spread of tic-like behaviors in Le Roy, as affected individuals were uploading videos of their symptoms onto these social media sites^4,5,6,7.

A similar phenomena occurred in Germany in June 2019 when German Neurologists saw a vast rise in FT strikingly similar to a popular YouTube Channel “Gewitter im Kopf [Thunderstorm in the Brain]”, staring a young man Jan Zimmerman (95, 96). The channel gained rapid popularity and has more than 2.2 million subscribers and 312 million views⁸. Zimmerman has a similarly large presence across multiple platforms. Individuals presented with near identical complex movements, vocalizations, and unique words or phrases often seen in Zimmerman's videos. Given the specific role of social media, a more specific term was suggested - mass social media-induced illness (MSMI) (95).

The benefits and risks of social media remain controversial. Some argue that social media and digital technology help maintain social connection despite social distancing and lockdowns (97). Social media can also serve as a platform for individuals to share their experiences, advocate, and educate about medical conditions including tics. However, drawing attention to tics and/or exposure to other's tic-like behaviors may serve as precipitating or perpetuating risk factors for both FT and CTD. While social media provides access to communities that may not be readily available locally, this may also serve as a medium for continued spread of FT. Additionally, overuse of social media is associated with anxiety, depression, and psychological distress all of which may serve as risk factors for FT (98, 99).

Tic-related videos are gaining popularity across social media and the rapid spread of tic-like behaviors is a global phenomenon. On TikTok alone, hashtags of #tourette (4.9 billion views) and #tic (3.1 billion) have grown substantially during the COVID-19 pandemic⁹, hence what some are calling “TikTok Tics”.

TikTok is a popular social media platform where users can create, watch and share short videos. TikTok has experienced a surge in monthly active users between January 2018 and August 2020. Globally TikTok's active monthly users has grown from 54 million users in January 2018 to over 1 billion users as of September 2021^10,11. For comparison of active monthly users across other social media platforms Facebook has 2.9 billion, YouTube 2.3 billion, WhatsApp 2 billion, Instagram 1.4 billion, Snapchat 538 million, and Twitter 436 million¹².

It is important to note that tic-related videos have grown substantially across multiple social media platforms and are not exclusive to TikTok. For example, TikTok influencer Evie Meg, better known as @thistrippyhippie, has 14 million followers for her tic-like behavior but also 791k followers on Instagram and 25 million views on YouTube^13,14,15. Her videos often feature complex movements, coprophenomena, unique triggers and context-dependent tics. This influencer discloses her diagnosis of FND and features other videos of functional dystonia and psychogenic non-epileptic spells (PNES).

Two studies assessed the phenomenology of tic-like behavior on TikTok based on expert review. Both studies found a high degree of coprophenomena, context-dependence, aggression toward others, and self-injurious behavior (7, 100). Tic-like behaviors were highly variable and nonstereotyped. While tic-like behavior often involved the face and neck, there was a higher percentage of movements involving arms or body. Tic severity was overall severe with a high degree of tic attacks reported. There was a female predominance with 64.3% female, 17.6% male, and 14.3% nonbinary based on self-report of gender identity in the user's profile (7). Mean age reported was 18.8 years old although limitations included lack of age disclosure as well as unclear timing of video to onset of symptoms (7).

While these descriptive analyses are important to exploring the relationship of social media and tic-like behaviors, these conclusions were based on observations of social media videos rather than in-depth in-person evaluations. Additionally, negative portrayals of CTD are more popular on social media (101) and may influence the phenomenology reviewed by these two studies.

There has been some question of secondary gain in use of social media. Many of these social media influencers have merchandise for purchase (7). Jan Zimmerman sells merchandise, a book and recently released a Google app with his most popular vocal tics including “tics of the month.” Evie Meg released her new book “My Non-Identical Twin: What I'd like you to know about living with Tourette's” (7, 102, 103). It is important to note that factitious disorders and malingering are distinctly different from FMD and are beyond the scope of this article.

While many of the features overlap with FT, there are emerging distinctive features (Figure 2, Supplementary Table 1). A more encompassing term is used, Functional Tic-Like Behaviors (FTLB) to better reflect the combined role of social media and the pandemic.

FLTB have a female predominance (11) with the exception of one report from Germany (96), which had a male predominance. It is possible that this is related to the German social media influencer previously discussed. Median age of FTLB onset ranges from 14.2 to 15.3 years old with initial presentations being abrupt onset, non-fluctuating, and predominately complex tic-like behavior (11, 96, 104). Studies note a higher prevalence of tic-like behavior involving the trunk and extremities relative to the expected rostro-caudal progression seen in CTD (11, 96, 104). Pringsheim et al. reported a higher proportion of anxiety and depression diagnoses in FTLB compared to primary tic disorders (11), whereas others have found no significant difference (96).

FTLB are associated with high prevalence of coprophenomena, odd words or phrases, self-injurious (SIB) and non-obscene socially inappropriate behavior (NOSIB) (7, 71). Additionally, unique or contextual triggers such as particular words, flashing lights, or loud noises can trigger the tics or tic attacks (96, 104). Common SIB include hitting, punching or slapping one's self. Conversely, NOSIB can present as hitting others, throwing or hitting objects (11, 104). Tic attacks and presence of other functional or somatic symptoms were commonly reported (104). There are more limited data and variability in the degree of suppressibility, family history of tics, and presence of premonitory urge in patients with FTLB (11, 96). Careful questioning may endorse exposure to tic-related videos on social media; however, it should be considered one of many risk factors and is not always found (11, 96).

Although the predominance of adolescent females is reported, other sociodemographic features associated with FTLB remain unknown. Further exploration of risk factors and social determinants of health would be useful for prevention and intervention planning.

There is mounting evidence on the neurological sequela of COVID-19 infections including new development of movement disorders. Although one may consider post-infectious or infectious phenomena of COVID-19, a recent review of de novo movement disorders related to COVID-19 infections did not report any cases of new tics or tic-like behavior (105).

However, the COVID-19 pandemic has profoundly affected the mental health of many individuals, including children and adolescents. Nearly 168 million children globally missed an entire year of school due to COVID-19 according to the United Nations Education, Scientific and Cultural Organization (UNESCO). In April 2020, 1.5 billion learners were affected by school closures in 195 countries and as of November 2021, 55 million learners were still impacted by school closures with lower socio-economic statuses disproportionally affected (106)^16,17.

Prior studies demonstrated both short- and long-term psychological effects of pandemics/epidemics including increased post-traumatic stress symptoms, anxiety, depression, helplessness, and risky behaviors (107–113). The overall rates of depression and anxiety are higher during COVID-19 than prior pandemics (114), with increased risk in females, adolescents, and remote learners (106, 107, 114–121). Periods of intense stress, such as the pandemic, can be associated with increased functional symptoms (122–124).

Parental stress, mental health, and wellbeing are also impacted during the pandemic, which is associated with poorer child wellbeing (125–128). Disruptions from the pandemic altered diets, sleep schedules, and social relationships. Additionally, parents reported interrupted access to medical care and to their support networks. Parents and/or caregivers suffered from isolation, employment changes, food insecurity, housing instability, and financial constraints all while balancing remote-learning and their child's wellbeing (125). Lower socioeconomic status, younger parents, and families of healthcare workers have been reported to be at increased risk of poorer wellbeing (129, 130). Additionally, there are increased reports of childhood adverse experiences during the pandemic, such as witnessed domestic violence, emotional abuse, and physical abuse (131, 132).

There has been an overall increase in new FMD presenting to neurology clinics during the COVID-19 pandemic (10). Despite this increase, individuals with preexisting FMD did not show significant variability or worsening of their symptoms during the pandemic (133). However, up to two-thirds of parents or individuals reported worsening of CTD symptoms (134, 135). Children with neurodevelopmental disorders, such as CTD, report higher behavioral and psychological impacts of the pandemic compared to peers (136). The same is true for children with preexisting mental health diagnoses (125). Acute psychosocial stressors, routine disruption, and increased mental health burden likely play a role in symptom exacerbation or development; however, these relationships need to be further explored (137).