Dental implants‐induced task‐specific oromandibular dystonia

Task-specificity is a unique characteristic of focal dystonia; that is, abnormal movements or postures are predominantly or even exclusively present under specific circumstances [1]. Task-specific oromandibular dystonia (OMD) is a rare condition, and reported exclusively as a result of excessive speech and playing a wind instrument [2–5]. Here we present a case of task-specific OMD following dental implant surgery. A 56-year-old housewife presented with a 1-year history of involuntary retraction of her lips while speaking. She underwent dental implant surgery 6 months earlier, but had neither a relevant medical history nor exposure to relevant medications. She did not have an occupation, hobby or religion requiring an excessive use of perioral muscles. She reported that her symptoms had not progressed after onset. The involuntary movements occurred when she vocalized, regardless of ordinary conservational speech, reading out loud or singing. The lips returned to the normal position immediately after vocalization stopped, and the symptom did not occur while eating or drinking (Video S1). She denied any discomfort in the implant insertion site. This involuntary movement was improved when she put her finger or a depressor on her tongue while speaking, but was not alleviated by chewing gum or sucking on a candy (Video S2). Neurological examination revealed no other neurological deficit. Over a 6-month follow-up, she received medications including procyclidine, metoclopropamide and dantrolene sodium, resulting in mild-to-moderate improvement without progression. Patterned and repeated involvement of the same perioral muscles along with aggravation by voluntary movements are compatible with the clinical characteristics of primary dystonia [1]. The presence of a sensory trick, namely the symptomatic alleviation by touching the tongue, provides additional evidence to diagnose as primary dystonia in this patient [1]. Because her symptom was present exclusively while speaking, it was diagnosed as task-specific OMD. Previously reported cases of speech-induced task-specific OMD were exclusively associated with long-term experiences of excessive speech due to occupation or religious rituals [2– 5], but our patient lacks this association. Peripheral injury, including dental procedures, is a potential predisposing factor to induce OMD [6], but none of the previous cases was task-specific. The causal relationship between dental implants and the development of OMD is unclear. However, OMD in this patient fits the criteria defining peripherally induced OMD suggested by Sankhla et al. [6] well, which include temporal relationship within a year, well documentation of the trauma, and anatomical relationship between the injured site and location of dystonia. The underlying mechanism for task-specific dystonia is still unclear, although deficient central nervous system inhibition, abnormal sensorimotor integration and maladaptive plasticity are suggested [7]. In addition to the longterm overuse of affected muscles, the present case may illustrate another potential relationship between peripheral injury and task-specific OMD.