One Step to Understanding Psychogenic Dystonia

Abstract & Commentary

By Claire Henchcliffe, MD, PhD, Associate Professor of Neurology and Neuroscience, Weill Cornell Medical College. Dr. Henchcliffe reports she is on the speakers bureau and advisory board for Allergan and Teva; speakers bureau for Boehringer-Ingelheim, GlaxoSmithKline, and Novartis; advisory board for Merz; and is a consultant for Gerson Lehman Group and Guidepoint Global.

Synopsis: Regional cerebral blood flow defines distinct patterns of disrupted metabolism in psychogenic vs “organic” dystonia, with decreased flow in motor and premotor cortex in psychogenic dystonia, but increased flow in subcortical structures.

Source: Schrag AE, et al. The functional neuroimaging correlates of psychogenic versus organic dystonia. Brain 2013;136(PT 3):770-781.

This study compares functional imaging of adult study participants with psychogenic dystonia, genetic dystonia, and healthy controls. Participants with psychogenic dystonia comprised six individuals who fulfilled accepted diagnostic criteria, were recruited by experienced movement disorders neurologists, had no serious medical comorbidity or major affective or psychotic disorders, and were without structural abnormalities on brain and cervical-spine MRI. As subjects with “organic” dystonia, five individuals with genetic dystonia associated with DYT1 gene mutation were enrolled, of whom four had generalized symptoms and one had mild foot and hand dystonia. Six matched healthy control subjects were included. All participants underwent H2 15O PET to assess regional cerebral blood flow (rCBF), averaged over three conditions: 1) at rest, 2) with the right foot inverted and plantar flexed (voluntarily for DYT1 and control subjects), and 3) with monitored paced ankle flexion-extension. When compared to controls, in psychogenic dystonia rCBF was increased in bilateral cerebellum, left globus pallidus pars interna, right caudate, and bilateral thalamus, and was decreased in left primary motor cortex (medial leg area), left supplementary motor area, and left thalamus. When compared to subjects with DYT1-associated dystonia, in psychogenic dystonia rCBF was increased in the cerebellum, putamen, thalamus, and the left subthalamic nucleus. In contrast, in DYT1-associated dystonia compared with psychogenic dystonia, rCBF was increased in the left primary motor cortex (medial leg area) and left premotor cortex, right parietal cortex, as well as right thalamus, and right caudate nucleus.

Commentary

Psychogenic movement disorders are challenging to diagnose and treat, and are common. It has been estimated that up to 30% of outpatient neurology referrals comprise cases in which neurological symptoms cannot be accounted for medically. Unfortunately, there are no objective tests that confirm a diagnosis of psychogenic disorder. Moreover, in suspected psychogenic dystonia, diagnosis is hampered by limitations of tests that confirm a known cause of dystonia, such as genetic mutation or cerebral structural abnormalities. Various criteria have been proposed, including those used in this study, by Gupta and Lang in 2009.1 According to the diagnostic classification, features supporting the diagnosis would involve symptom improvement with suggestion, placebo, psychotherapy, physiotherapy, or while “unobserved,” and a “clinically established” diagnosis would involve features that do not fit with a known clinical condition, with “false” signs, psychiatric disturbance, and multiple somatizations. Other clues from physical examination include variability of symptoms, distractibility, and suggestibility. Although such formal criteria are highly valuable, they also highlight the limited understanding of psychogenic disease and the critical need to better understand, diagnose, and track treatment effects in these disorders. Again, dystonic symptoms present a particular challenge as dystonia may fluctuate and appear bizarre at times, and psychiatric disease is common enough that it is not a reliable enough indicator of a psychogenic etiology. As such, the present study is very important in that it is the first to focus specifically on psychogenic dystonia. Moreover, the study included a very homogeneous cohort in terms of physical presentation — with fixed dystonia of a lower limb chosen as characteristic of psychogenic dystonia based on prior studies. The investigators found that rCBF measures clearly highlight anatomically distinct differences between both psychogenic and “organic” dystonia, and also between psychogenic dystonia and control participants.

The finding that rCBF is decreased in primary motor cortex but increased in basal ganglia and cerebellum in psychogenic vs “organic” dystonia leads the authors to propose a cortical-subcortical differentiation. It is therefore very interesting that organic dystonia, but not psychogenic dystonia, has been associated in previous studies with increased cortical plasticity. Although the study has obvious weaknesses, including small numbers of participants and diagnoses in psychogenic cases made on a clinical basis, it does provide hope for developing better understanding of underlying mechanisms and testing methodologies.

Reference

1. Gupta A, Lang AE. Psychogenic movement disorders. Curr Opin Neurol 2009;22:430-436.