F079 Functional movement disorders in huntington disease gene expansion carriers and individuals at risk: more common than we thought?

<h3>Objective</h3> Our goal was to investigate the occurrence of functional movement disorders (FMDs) in Huntington disease gene expansion carriers (HDGECs) and individuals at risk of harboring a pathological CAG expansion in the huntingtin gene (at-risk individuals). Additionally, we sought to characterize the phenomenological spectrum of any identified FMDs. <h3>Background</h3> FMDs can be difficult to diagnose, especially when they overlay movement disorders of organic origin. Although the co-occurrence of FMDs with neurological disorders is well-documented and quite common, there is limited understanding of FMDs in Huntington disease (HD). <h3>Methods</h3> We examined the phenomenology of movement disorders in HDGECs and persons at-risk attending routine outpatient appointments emphasizing the identification of potential overlaying functional symptoms based on their typical clinical features and positive signs (suggestibility, variability, distractibility, entrainment, enhancement with attention, motor inconsistency, incongruency). <h3>Results</h3> We present a case series of fifteen individuals, including fourteen HDGECs (two in the late stags) and one at-risk individual. The cohort consisted of seven males and eight females, aged 33 to 66 years. In HDGECs, the onset of FMDs primarily occurred at a prodromal stage or early stages of the disease, except for two cases where FMDs manifested at an advanced stage. Predictive testing of at-risk individuals revealed no pathological CAG expansion in the huntingtin gene. Among the patients, five exhibited mixed phenomenology of FMDs, while fourteen presented a hyperkinetic phenotype, including aggravated chorea, functional myoclonus, tics (vocal and motor), and dystonia. One patient also reported whole-body pain and subjective bilateral monocular double vision. Triggers included COVID-19 vaccination/infection and psychological stressors, such as the anticipation of HD onset. One HDGEC later died due to cardiopulmonary arrest, two others achieved remission, and the rest showed varying degrees of improvement with certain therapeutic approaches. <h3>Conclusions</h3> Being a potentially treatable aspect of the phenotype, FMDs might be considerably underreported in HDGECs and at-risk individuals. A thorough analysis of FMDs in individuals from HD families is required.