Dystonia is a movement disorder characterized by abnormal, involuntary, and excessive co-contractions of agonist and antagonist muscles. It can affect one or several parts of the body and manifest itself as twisting movements, tremors or abnormal postures (1). When focal, it can affect the upper limb, the eye or the neck, resulting in writer’s cramp, blepharospasm and cervical dystonia, respectively.
Dystonia can be classified based on its clinical features or its underlying causes (2). A distinction is often made between two clinical phenotypes: an organic form of cervical dystonia (CD) and a functional form of it (f-CD) – also called psychogenic. The term organic refers to various entities where a neurological substrate is suspected or demonstrated to explain the physiopathology. By extension, it refers sometimes to idiopathic dystonia with typical clinical presentation. The term organic is mainly used in opposition to psychiatric entities such as psychogenic dystonia that is considered to be a functional movement disorder (FMD). Nowadays, both are regarded as clinical forms with different positive signs and diagnosis (2–4). Nonetheless, because of partly overlapping features, the distinction varies between experts giving the diagnosis (5,6); making the distinction between the two diagnoses a key challenge.
Diagnosis of functional dystonia is mainly based on clinical criteria (3,4). However, a clinical study showed that about 37 of 87 idiopathic cervical dystonia patients were initially misdiagnosed as psychogenic (7). According to Dauer et al., (1998) “The only way to make the diagnosis with relative certainty is by finding persistent disappearance of the movements with psychiatric therapy” – when speaking about functional dystonia (8). Furthermore, the misdiagnosed patients receive the same chronical palliative treatment as the other dystonic patients yet without long-lasting improvement.
More in line with present nomenclature, our study includes idiopathic, adult-onset, focal, isolated cervical dystonia (CD) and functional cervical dystonia (f-CD). However, for the sake of simplicity, we will be referring to them as organic (CD) and functional (f-CD).