Decade of progress in motor functional neurological disorder: continuing the momentum

Correspondence to Dr W Curt LaFrance, Jr, Psychiatry and Neurology, Rhode Island Hospital, Providence, RI 2903, USA; [email protected]

Introduction

Functional neurological disorder (FND), also known as conversion disorder, is a common, disabling and costly condition at the intersection of neurology and psychiatry.^{1 2} While of interest to founding leaders across the clinical neurosciences in the late 19th century, FND was largely abandoned by academics and researchers alike during the late 20th century.^S1 The rationale for these difficulties were based in part on a Cartesian dualism of the brain and mind, limited neuropathophysiologic understanding and few evidence-based treatments.^S2 In the 21st century, a resurgence of interest in FND has occurred, catalysed by improved diagnostic specificity, an expanding ‘toolbox’ of treatments and new pathophysiological models that embrace patient-centred biopsychosocial formulations.³ A newly formed professional society (www.fndsociety.org), authoritative FND textbooks^{4 5} and recent special journal issues on this topic have further energised clinical and research efforts in FND.

In this narrative review, we highlight important advancements and their implications for motor FND (mFND) over the past 10 years (2011–2020)—spanning functional movement disorder and functional limb/face weakness. We use a transdiagnostic approach across the range of functional motor symptoms given high phenotypic overlap across populations (eg, functional tremor with concurrent functional weakness in the same limb).^S3 Isolated functional (psychogenic non-epileptic/dissociative) seizures, functional speech/voice disorder, functional cognitive disorder, functional sensory deficits and the spectrum of functional somatic disorders are beyond the scope of this article and have been reviewed elsewhere.^{S4 S5} Sections here detail recent developments in diagnosis, mechanisms, aetiological factors, treatments and stigma in patients with mFND. In each content area, future directions are also suggested, aimed at continuing the momentum of the past decade.

Diagnosis

New developments

Establishing the diagnosis of mFND has been made more practicable,^S6 as physical examination findings with diagnostic specificity have been identified (eg, Hoover’s sign with an estimated specificity of 95.7%–99.9%).⁶ Educational efforts have also made neurologists more confident in their ability to accurately diagnose patients with mFND, discouraging extensive laboratory testing unless a comorbid neurological disorder is suspected.⁷

The Diagnostic and Statistical Manual of Mental Disorders-Fifth Edition (DSM-5) criteria for FND include the diagnostic features of inconsistency and incongruity on examination, emphasising...