Objective: This report highlights how challenging the differential diagnosis between organic and functional motor disorders may be. Indeed, atypical presentations and overlapping features of movement disorders presented during the pediatric age may result in misleading diagnoses and treatment.

Background: FMDs were reported with a prevalence of 6,3% of acute hyperkinetic movement manifestations in youngsters. The occurrence of many rare genetic and acquired conditions causing movement disorders in children makes diagnosing FMDs possibly challenging.

Method: We report a 14-year-old male admitted to our Movement Disorders (MDs) pediatric unit at the age of 13 with a previous diagnosis of stereotypes and then FMDs because of the recurrence of twisting-like movements involving the right part of the body with a caudal-rostral progression of the lower and upper limbs. On examination, these paroxysmal motor manifestations were not stoppable or modulated by distractible manoeuvres, and in subsequent evaluations, no signs of inconsistency could be found. Prolonged clinical observation and home video analysis also revealed that sudden voluntary movements triggered them. In the suspect of a paroxysmal kinesigenic dyskinesia, Next Generation Sequencing (NGS) panel for genetic MDs was carried out.

Results: NGS disclosed a de novo heterozygous pathogenic variant in the proline-rich transmembrane protein 2 (PRRT2) gene (c.649delC; p.Arg217fs*12), compatible with the diagnosis of genetic dystonia type 10 (DYT-10). Mutation of PRRT2has been widely studied as a causative of paroxysmal kinesigenic dyskinesia responsive to low doses of carbamazepine. Accordingly, carbamazepine was titrated up to 100 mg/day, with complete remission of symptoms within one week.

Conclusion: While the relevance of our clinical observation lies in the specific impact of FMDs misdiagnosis on the treatment and outcome of PRRT2-related movement disorders, it also adds novel insights into the differential diagnosis between genetic movement disorder and pediatric functional motor disorders (FMDs), according with the new diagnostic criteria for a roll-in diagnosis of FMDs in DSM-5, based on the pediatric neurological phenomenology

References: Ganos, C.; Aguirregomozcorta, M.; Batla, A.; Stamelou, M.; Schwingenschuh, P.; Münchau, A.; Edwards, M.J.; Bhatia, K.P. Psychogenic Paroxysmal Movement Disorders–Clinical Features and Diagnostic Clues. Parkinsonism Relat. Disord. 2014, 20, 41–46, doi:10.1016/j.parkreldis.2013.09.012.

Stone, J.; Carson, A.; Duncan, R.; Coleman, R.; Roberts, R.; Warlow, C.; Hibberd, C.; Murray, G.; Cull, R.; Pelosi, A.; et al. Symptoms “unexplained by Organic Disease” in 1144 New Neurology out-Patients: How Often Does the Diagnosis Change at Follow-Up? Brain J. Neurol. 2009, 132, 2878–2888, doi:10.1093/brain/awp220.

Méneret, A.; Grabli, D.; Depienne, C.; Gaudebout, C.; Picard, F.; Dürr, A.; Lagroua, I.; Bouteiller, D.; Mignot, C.; Doummar, D.; et al. PRRT2 Mutations: A Major Cause of Paroxysmal Kinesigenic Dyskinesia in the European Population. Neurology 2012, 79, 170–174, doi:10.1212/WNL.0b013e31825f06c3.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/prrt2-paroxysmal-dyskinesia-mimicking-functional-motor-disorders-a-pediatric-case/