Characteristics of two distinct clinical phenotypes of functional (psychogenic) dystonia: follow-up study.

Background: The fixed dystonia phenotype was originally established as a prototype of functional dystonia. Nevertheless, in recent reports different functional dystonia phenotypes have been recognized with dystonic movement comprising phasic instead of tonic contraction.

Objectives: To examine clinical characteristic in all patients with dystonia who fulfilled the criteria for functional movement disorders irrespective of phenotype in an attempt to determine parameters of clinical presentations that might impact the disease progression pattern and outcome.

Methods: Patients presented with dystonia features incompatible with organic disease without other features required for the diagnosis of functional movement disorders were analyzed and prospectively followed-up. The two-step cluster analysis was performed to obtain the subgroups of dystonia phenotypes.

Results: The two-step cluster analysis extracted two subgroup of patients. Patients of the first cluster (68.8%) presented with "mobile" dystonia (84.9%), of cranial/neck/trunk localization (90.9%), fluctuated clinical course (69.7%), with frequent additional movement or other functional neurological disorders (63.6%) during follow-up. In the second cluster (31.2%) all of the patients presented with "fixed" dystonia of extremities, and the clinical course was characterized by either the disease progression (60%), or continuous without improvement (26.7%), and rare occurrence of additional functional neurological disorders (13.3%).

Conclusion: In terms of clinical and demographic features as well as pattern of disease progression there are two clinical phenotypes in patients with functional dystonia. Distinctive features of incongruence and inconstancy are characteristic for "mobile" functional dystonia subgroup of patients.