LAUSR

We appreciate the comments submitted in response to our recent article describing—in line with reports from other groups of expert clinicians from Canada, USA, UK, and Germany—a presentation of functional ‘tic-’ and ‘Tourette-like’ behaviour. There is general agreement among leading Tourette experts that these symptoms represent a phenotype of a functional movement disorder (FMD). Remarkably, this kind of FMD phenotype has never been described before, though functional tics are a well-known, albeit rare presentation of FMD. Similar to others, we point out that functional ‘Tourette-like’ behaviour can be differentiated from tics based on several clinical characteristics including relatively rapid onset of mainly complex and progressively increasing vocalizations and movements in adolescence. While several authors speculated that change in FMD phenotype might be related to the COVID-19 pandemic, others also suggested an influence by social media. Based on a thorough examination of patients presenting in our specialized Tourette outpatient clinic and after rigorous evaluation of ‘Tourette syndrome’-related videos on social media, we identified a remarkable overlap between symptoms presented by our patients and the German influencer Jan Zimmermann on his YouTube channel ‘Gewitter im Kopf’ (‘Thunderstorm in the brain’). Evenmore: symptoms started only after the channelwas launched and patients confirmed having watched these videos before symptom onset. Thus, we believe that the onset of this new ‘Tourette-like’ FMD presentation can be best explained as an outbreak of the motor variant of mass sociogenic illness (MSI). Since symptoms spread solely via social media, we suggested the more specific term ‘mass social media-induced illness’ (MSMI). Conelea et al. (doi:10.1093/brain/awac028) argue that making a diagnosis based on videos ‘conflicts with the ethical standard that psychiatrists refrain from offering a professional opinion without examination’. With respect to psychiatric diagnoses, in general, we agree with this statement. However, making the diagnosis of movement disorders—including FMD—based on videos has a long tradition. In addition, there is a large agreement among Tourette experts that most symptoms presented by Jan Zimmermann on his YouTube channel—but also of several other influencers on social media—represent a manifestation of FMD instead of Tourette syndrome. We believe that functional ‘Tourette-like’ behaviour can—and should—be differentiated from tics in Tourette syndrome at least in order to enable correct—and avoid inappropriate—treatment. In contrast, Conelea et al. argue that Tourette syndrome and FMD represent different parts of a spectrumof one and the same disease, with functional ‘Tourette-like’ behaviour being not a ‘modal Tourette syndrome presentation’. Accordingly, they suggest not to view Tourette syndrome and functional ‘Tourette-like’ behaviour as a ‘heterogeneous group’. This opinion is in clear contrast to recently published articles on functional ‘Tourette-like’ behaviour and experts’ statements, e.g., from the Tourette Association of America (TAA), the European Society for the study of Tourette syndrome (ESSTS), and the University of Calgery. Conelea et al.’s position is also contrary to ICD (F95.2: Tourette syndrome, but F44.4: FMD) and DSM (Tourette syndrome: 307.23, but functional neurological disorder including FMD: 300.11) classifications, where tic and functional disorders are classified in different categories. Conelea et al.’s argumentation creates the impression that some patients with FMD may prefer and desire the diagnosis of Tourette syndrome instead. Following Conelea et al.’s line of reasoning making diagnoses based on similarities in clinical presentations instead of underling pathology, one would also have to diagnose patients with so called psychogenic non-epileptic seizures (PNES) as having epilepsy. The argument that both types of movements, tics and FMD, may occur within individuals does not constitute a valid argument against such a ‘categorical distinction’. About 30% of patients with epilepsy suffer in addition fromPNES. Similarly,wemade the additional diagnosis of Tourette syndrome in 47% of our patients with functional ‘Tourette-like’ behaviour (unpublished data). However, we agree