Parkinsonism and Related Disorders 20 (2014) 1287e1289
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Disease modeling in functional movement disorders Roberta Pellicciari, Maria Superbo, Angelo Fabio Gigante, Paolo Livrea, Giovanni Defazio* Department of Basic Medical Sciences, Neuroscience and Sense Organs, Aldo Moro University of Bari, I e 70124 Bari, Italy
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Article history: Received 28 March 2014 Received in revised form 7 August 2014 Accepted 9 September 2014
Introduction: The mechanisms underlying functional movement disorders are poorly known. We examined whether experience of a movement disorder model in the family and/or the friendships contributes to functional movement disorders. Methods: The hypothesis was tested in a caseecontrol study including 33 patients with functional movement disorders and 66 age- and sex-matched patients with organic movement disorders and using a conditional logistic multivariable analysis (adjusted by age, education, disease duration, chronic medical illnesses and clinical phenotype). Results: Case-control comparison yielded a signiﬁcant association between functional movement disorders and exposure to phenotypically congruent movement disorder models (Odds ratio, 3.9, p ¼ 0.01), mainly when disease model came from friendships (Odds ratio, 5.9, p ¼ 0.04). By contrast no association was found between functional movement disorders and phenotypically different neurological or non neurological disease models. A signiﬁcant inverse relationship between exposure to a phenotypically concordant movement disorder model and age of disease onset was also observed. Conclusions: These ﬁndings support disease modeling as a factor contributing to the phenomenology of functional movement disorders. © 2014 Elsevier Ltd. All rights reserved.
Keywords: Movement disorder Functional Psychogenic Disease model
1. Introduction “Functional” or “psychogenic” movement disorders refer to non-voluntary conditions that differ from factitious disorders or malingering and are unexplained by organic disease [1e4]. The cause and mechanisms underlying functional movement disorders (FMDs) are poorly known. Although a psychological cause is frequently presumed, examination reveals an underlying psychiatric condition only in a proportion of cases [5e7]. Recently, Shill and Gerber proposed that experience of a movement disorder may provide a model for patients to unconsciously produce a FMD . In their original sample, however, disease model was almost exclusively identiﬁed among relatives , whereas exposure to a disease model can obviously take several forms, including not only familial environment but also friendships, work environment, and media. Moreover, one third of Shill and Gerber's patients who reported a disease model were exposed to a disease that did not ﬁt FMD phenotype . Overall, these observations raised doubt about the signiﬁcance and strength of the association. Finally, it remained
* Corresponding author. Tel.: þ39 080 5478511; fax: þ39 080 5478532. E-mail address: [email protected]
(G. Defazio). http://dx.doi.org/10.1016/j.parkreldis.2014.09.017 1353-8020/© 2014 Elsevier Ltd. All rights reserved.
unclear whether disease modeling is independent of, or relates to, other FMD features. In this caseecontrol study comparing patients with FMDs and organic movement disorders (OMDs) we investigated exposure to disease models in two environments, family and friendships. We also examined the relationship between disease modeling and relevant FMD clinical features. 2. Patients and methods Study subjects were selected among outpatients attending our movement disorder clinic from November 2011 to July 2013. In the study period, FMD was diagnosed in 33 patients according to Fahn and Williams criteria : a documented diagnosis was made in 5 patients reporting persistent relief of FMD by placebo; a clinically established diagnosis was made in 25 patients suffering from incongruent or inconsistent movement disorders and also reporting one or more among multiple somatizations, psychiatric disturbances and false neurological signs; and a probable diagnosis was assigned to 3 patients who presented with incongruent or inconsistent movement disorders. Each FMD patient was sex- and age (±3 years)-matched with two control outpatients suffering from adult-onset dystonia, adult-onset tremor, parkinsonism, and idiopathic ataxia. Case and control patients could not be matched by phenotype because FMD patients may experience multiple types of abnormal movements. One medical examiner used a standardized spreadsheet to collect data non age, sex, years of schooling, age of disease onset, duration of disease, movement disorder phenotype, sudden onset, somatizations, false neurological signs, psychiatric and medical illnesses (diagnosed on the basis of adequate medical documents), and
R. Pellicciari et al. / Parkinsonism and Related Disorders 20 (2014) 1287e1289
exposure to a possible disease model before movement disorder onset. Case and control patients were categorized according to the clinical dominant phenotype, i.e. tremor, dystonia, gait disturbance. Exposure to a disease model was routinely investigated by asking case and control patients about neurological and non neurological problems in the family (ﬁrst-degree relatives) and circle of friends. The person carrying the disease model should have been observed by case/control patient for one year or more prior to the onset of his/her movement disorder. In FMD patients who had more than one functional phenotype, congruency of modeling was tested for the dominant phenotype. Conditions like hypertension, diabetes, and hyperlipidemia were not considered as disease models. The examiner was not blinded to the case/control status but she was unaware of study hypotheses until the end of the recruitment phase. The study was approved by the local ethics committee and written informed consent was obtained by participating patients. Data were analyzed by Stata 11 package. Unless otherwise speciﬁed data were expressed as means ± SD. Differences between groups were examined using ManneWhitney U test and chi-square test or Fisher's test as appropriate. Conditional logistic regression analysis with ﬁxed case/control ratio (1:2) estimated the relationship of prior exposure to a disease model to case/control status. Odds ratio (OR), 95% conﬁdence interval (CI) and p values were computed. Estimates were adjusted by the dominant movement disorder and the number of different abnormal movements detected in each subject. Age, years of schooling, disease duration (continuous variables) and chronic medical diseases were included in the model as further potential confounders. p values