Psychogenic axial myoclonus: clinical features and long-term outcome

It has been increasingly recognized that the majority of patients with a diagnosis of idiopathic propriospinal myoclonus have either a subsequent clinical course or electrophysiological features indicating that the likely etiology is psychogenic. However, the clinical features of psychogenic axial myoclonus and the long-term outcome have not yet well characterized.

Here we describe clinical findings with representative videos and long term outcomes of 76 patients with an electrophysiologically established diagnosis of psychogenic axial myoclonus.

Thirty-seven patients were male. Mean age at onset of symptoms was 40.1 ± 15.1 years. Thirty-two patients (42.1%) presented with isolated axial myoclonus, while 44 patients (57.9%) presented additional features, including involvement of face or limb. In all patients but six (7.9%), the axial myoclonus was in flexion. In more than one-third of patients (42.1%), jerks were multifocal, meaning that there was no clear stereotyped pattern of jerks. Comparison between groups stratified according to the clinical outcome, revealed "delay of diagnosis" as the only predictor of worse outcome.

We describe here the clinical features and long-term outcome on the largest series of patients with psychogenic axial myoclonus reported in the literature. The description of our series highlights a number of clinical features, which may help neurologists to reach a correct diagnosis on clinical grounds alone. Delay in diagnosis of a psychogenic disorder has a negative effect on long-term outcome.