Between Habit and Mannerism: Idiosyncratic Motor Behavior

What movement peculiarities are not pathological entities? Ingrained habits and mannerisms. Habits are learned behaviors that respond to a trigger or stimulus and form through repetition, providing a sense of reward and eventually becoming self-perpetuating.1 Repetitive self-soothing habits or ritualistic manipulations of the body (ie, nailbitting or twirling hair) reinforce a mental framework, ingraining behaviors even without a stimulus or deliberation.2 Mannerisms are exaggerated or distinctive habits almost exclusively reported in patients with schizophrenia.3 We describe two individuals whose self-soothing motor behaviors persisted beyond their original triggers, leading to movements that concerned their physicians about possible diagnoses of tics, dystonia, or functional movement disorder. We suggest referring to these tic-like mannerisms as idiosyncratic motor behavior, given the volitional control and the absence of perceived disability. Case 1 is a 44-year-old woman with 20 years of jerky, non-rhythmic, and non-stereotypical shoulder and lower jaw movements that developed to relieve neck stiffness. She denied an urge to perform the movements or relief upon their execution. Physical examination showed voluntarily suppressible head tilting and shoulder elevation episodes that were repetitive and superficially similar but non-identical (Video 1). Case 2 involves a 48-year-old woman with 10 years of myofascial pain syndrome and fibromyalgia who developed neck movements that persisted despite pain resolution with duloxetine. She reported some need to perform the movements, but could stop them at will. The movements were repetitive but non-stereotypical and variably included the neck and/or one or both arms (Video 2). Neither woman reported a personal or family history of tics, obsessive-compulsive symptoms, or exposure to dopamine-blocking agents. Relieving behaviors may outlast the resolution of their trigger, turning into habits or, in a heightened expression (admittedly in the eye of the beholder), mannerisms. We suggest referring to them as idiosyncrasies or idiosyncratic motor behaviors. Lacking a template from our field, we adapt the American Psychological Association definition of idiosyncrasy: “a habit or quality of body or mind peculiar to an individual.”4 They are suggestive of stereotypies and complex tic disorders. Unlike either, idiosyncrasies include a larger repertoire of motor behaviors that recruit similar body regions but do so without exact repetition (i.e., a shoulder can be moved vertically first, and forward or laterally later). Case 1 may have undiagnosed Tourette's: nose rubbing in the video suggests a simple motor tic. This could have predisposed her to develop idiosyncrasies. However, in neither case was there a personal or family history or endorsement of premonitory urges. Finally, unlike functional movement disorder, agency was preserved. Patients owned their movements and acknowledged them as “bad habits,” however inadequate a label. In sum, self-soothing behaviors may become entrenched as motor traits and evolve into habits or idiosyncrasies. They do not require a workup, and in most cases do not warrant symptomatic treatment—just reassurance about their benign nature. (1) Manuscript Preparation: A. Writing of the first draft, B. Review and Critique, C. Video editing. J.P.: 1A, 1B, 1C. Z.Y.: 1B. B.T.: 1B. Am.L.: 1B. An.L.: 1B. A.J.E.: 1A, 1B. Ethical Compliance Statement: This manuscript was carried out in accordance with the World Medical Association Declaration of Helsinki. IRB approval was waived, given the type of manuscript and that no identifiable personal information is included. The patient signed a written consent-to-disclose form and had the opportunity to review the information included. 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 Conflicts of Interest: No specific funding was received for this work. The authors declare that there are no conflicts of interest relevant to this work. Financial Disclosures for the Previous 12 Months: AJE has received grant support from the NIH and the Michael J. Fox Foundation; personal compensation as a consultant/scientific advisory board member for Mitsubishi Tanabe Pharma America (formerly, Neuroderm), Amneal, Acorda, Abbvie, Bial, Supernus (formerly, USWorldMeds), NeuroDiagnostics, Inc (SYNAPS Dx), Intrance Medical Systems, Inc., Merz, Praxis Precision Medicines, Citrus Health, and Herantis Pharma; Data Safety Monitoring Board (chair) of AskBio; and publishing royalties from Lippincott Williams & Wilkins, Cambridge University Press, and Springer. He is co-inventor of the patent “Compositions and methods for treatment and/or prophylaxis of proteinopathies” with which he cofounded REGAIN Therapeutics to fund preclinical studies. He has no financial relationship with the company and has relinquished the right to any personal income from future treatments. AJE owns no stock in any pharmaceutical company with which he has an advisory relationship. AEL has served as an advisor for AbbVie, AFFiRis, Alector, Amylyx, Aprinoia, Biogen, BioAdvance, Biohaven, BioVie, BlueRock, BMS, Cavion, CoA Therapeutics, Denali, Janssen, Jazz, Lilly, Novartis, Paladin, Pharma 2B, PsychoGenetics, Roche, Sun Pharma, and UCB; received honoraria from Sun Pharma, AbbVie and Sunovion; received grants from Canadian Institutes of Health Research, Edmond J. Safra Philanthropic Foundation, Krembil Brain Institute, Michael J. Fox Foundation, Parkinson Foundation, Parkinson Canada, and The Rossy Foundation; has served as an expert witness in litigation related to paraquat and Parkinson's disease, received publishing royalties from Elsevier, Saunders, Wiley-Blackwell, Johns Hopkins Press, and Cambridge University Press. All other authors have nothing to declare. Author disclosures are available in the Supporting Information. Data sharing not applicable to this article as no datasets were generated or analysed during the current study. Data S1. Disclosures Form. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

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