On Differences between Gilles de la Tourette Syndrome and Psychogenic/Functional Tics: A Narrative Review

A tic is a sudden, rapid, recurrent, nonrhythmic motor movement or vocalization. Motor and phonic tics in a course of over 1 year that first occured before 18 years are the main features of Gilles de la Tourette syndrome (GTS). Psychogenic/functional (P/F) tics were considered as a diagnosis made per exlusionem in lack of agreement of diagnostic criteria. Recently, emphasis is in rather highlighting positive signs when making diagnosis of P/F tics. Several features in clinical course are important to differentiate GTS from P/F tics. Some of them are acute onset in adulthood, precipitation by physical event, absent family history of tics, variable, complex and inconsistent phenomenology, suggestibiity, distractibility. Premonitory urge, feeling of excessive energy and being 'wound up' prior tic, is a usual feature of GTS unlike in P/F tics. If present, such premonitory urge have different qualitative and quantitative marks. Another possible diagnostics tool could be the beireitshaftspotential, an event-related electrical potential associated to initiation of movement which is divided in two phases, early (B1) and late (B2) phase. Early phase, whose occurence in some papers has been reported prior P/F tics, is absent prior performed tic in GTS. In everyday clinical practice differentiating GTS from P/F tics is often very challenging but taking proper medical history, paying more attention to positive signs and possibly using electroneurophysiology tests could contribute in making the right diagnosis.