Stress and functional neurological disorders: mechanistic insights

Correspondence to Dr Roxanne C Keynejad, Section of Women’s Mental Health, Health Service and Population Research Department, Institute of Psychiatry Psychology & Neuroscience, King’s College London, London SE5 8AF, UK; [email protected]

Introduction

Functional neurological disorder (FND), also known as conversion disorder, has been historically conceptualised as the archetypal stress-related condition, but current evidence suggests that historical and precipitating stressors are neither necessary nor sufficient to cause the disorder. The role of stress, particularly severe traumas, in the aetiology of FND remains controversial, but there is consistent evidence that such experiences are major risk factors for, and of mechanistic and therapeutic relevance to, a significant proportion of cases.¹ in this perspective article, we review mechanistic insights into FND provided by the latest neurobiological stress research.

Multifactorial, biopsychosocial models predominate for FND, but details of biological mechanisms remain elusive. However, recent research in other fields, from basic neuroscience to mechanistic studies of other stress-related disorders, is starting to reveal insights into the molecular processes potentially underpinning interactions between biological vulnerability (diathesis) and environmental stressors, as part of a ‘stress-diathesis’ model. Furthermore, a growing body of literature shows how both early life and precipitating stressors play an aetiological role in physical as well as mental health disorders. Such developments have the potential to shape our understanding of FND’s pathogenesis, with wider implications for our understanding of functional disorders affecting other bodily systems.

FND is suspected when neurological symptoms arise in the absence of identifiable neuropathology or pathophysiological disease mechanisms. Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5) reflects the fact that FND is not a diagnosis of exclusion, but has distinct ‘positive’ clinical features differentiating it from other disorders (box 1).² FND is common, often causes severe and chronic disability, but is comparatively under-researched. Many questions about its aetiology await clarification.(1 s)

Box 1

DSM-5 functional neurological symptom disorder (conversion disorder) diagnostic criteria

• One or more symptoms of altered voluntary motor or sensory function.

• Clinical findings provide evidence of incompatibility between the symptom and recognised neurological or medical conditions.

• The symptom or deficit is not better explained by another medical or mental disorder.

• The symptom or deficit causes clinically significant distress or impairment in social, occupational, or other important areas of functioning or warrants...