Diagnostic Comparison of DSM-5-TR and ICD-11 for Conversion Disorder (Functional Neurological Symptom Disorder)
Both DSM-5-TR and ICD-11 have moved toward requiring positive clinical signs of internal inconsistency or incongruity with recognized neurological disease, which represents a major strength by reducing reliance on psychological factors that are difficult to operationalize and often absent at presentation.
Key Strengths of DSM-5-TR
Positive Neurological Signs Requirement
- DSM-5-TR requires clinical findings demonstrating internal inconsistency or incongruity with recognized neurological disease, shifting away from the problematic requirement to identify psychological stressors that may not be temporally associated with symptom onset 1.
- The criterion for positive neurological signs (e.g., Hoover's sign, tremor entrainment, give-way weakness) allows neurologists to make the diagnosis based on observable clinical examination findings rather than inferring psychological causation 1.
Symptom Subtype Expansion
- DSM-5-TR includes a cognitive symptoms subtype, recognizing the phenotypic heterogeneity of functional neurological presentations beyond traditional motor and sensory symptoms 1, 2.
- The classification acknowledges that symptoms can include weakness, numbness, events resembling epilepsy or syncope, and cognitive disturbances, capturing the full spectrum of presentations 1, 2.
Theoretical Neutrality
- The alternative terminology "Functional Neurological Symptom Disorder" is theoretically neutral and more acceptable to both patients and practitioners than "conversion disorder," which implies psychogenic causation 1.
Key Strengths of ICD-11
Clinical Utility and Usability
- In multinational field studies of 928 clinicians across all WHO regions, 82.5%–83.9% rated ICD-11 as quite or extremely easy to use, accurate, clear, and understandable—significantly higher than ICD-10 3.
- ICD-11 achieved higher diagnostic accuracy and perceived clinical utility than ICD-10 in vignette-based assessments across multiple disorder categories 3.
Longitudinal Tracking Capabilities
- ICD-11 permits coding of episodicity and current status (first episode, multiple episodes, continuous course; currently symptomatic, partial remission, full remission), enabling clinicians to monitor symptom trajectories over time 3.
- Dimensional symptom specifiers allow severity rating across multiple domains at each assessment, supporting flexible treatment planning without strict temporal symptom counts 3.
Critical Weaknesses Shared by Both Systems
Lack of Operational Definitions for "Disproportionate" Criteria
- Both DSM-5-TR and ICD-11 rely on "excessive" or "disproportionate" descriptors that lack operational definitions, creating risk of pathologizing normal illness responses and appropriate health-seeking behavior 3.
- The absence of clear thresholds for what constitutes "incongruity" with neurological disease leaves substantial room for subjective clinical judgment and potential diagnostic error 3.
Insufficient Evidence for Psychological Factor Requirement
- While DSM-5-TR relegated psychological factors to accompanying text rather than mandatory criteria, the evidence for both positive psychological signs and positive neurological signs remains limited, with prospective studies of inter-rater reliability and validity still needed 4.
- In complex cases, the absence of concurrent psychological distress in temporal association with neurological symptoms should not automatically support the diagnosis, as demonstrated by cases where extensive medical work-up initially appears negative but ultimately reveals organic pathology 4.
Biological Validation Deficit
- Both systems lack neurobiological dimensions and biological grounding, relying solely on clinically observable symptoms rather than underlying pathophysiology 5.
- This produces diagnostically heterogeneous categories that cannot guide treatment selection based on mechanisms, reducing potential for precision interventions 5.
Methodological Limitations of Supporting Evidence
Field Study Bias
- Selection bias may have inflated ICD-11 performance estimates because clinicians favorable to the new system were more likely to enroll, particularly in online studies with self-registration 3, 5.
- Vignette-based designs employed prototypical cases that do not capture the complexity of real-world presentations (e.g., comorbidities, cultural variations, atypical symptom patterns), limiting generalizability of reported superiority 3, 5.
- Participants' awareness of being studied could alter diagnostic behavior, meaning study results may not reflect routine clinical decision-making 5.
Critical Clinical Pitfalls to Avoid
Premature Diagnostic Closure
- The absence of clear proof of biological dysfunction should not lead automatically to the diagnosis of functional neurological symptom disorder; the work-up should include repeated psychological and neurological assessments in close collaboration, particularly in complex patients 4.
- Even when initial investigations (including D-dimers, routine imaging) are negative, organic pathology such as deep vein thrombosis with crossed embolus can be missed if clinicians prematurely commit to a functional diagnosis 4.
Interdisciplinary Assessment Requirements
- An interdisciplinary assessment based on individual evaluation of all neurological and psychosocial findings is essential, as neither positive psychological criteria alone nor positive neurological signs alone provide sufficient diagnostic certainty 4.
- The differential diagnosis represents a clinical challenge requiring collaboration between neurology and psychiatry, as patients typically present initially to neurologists who may use different concepts and terminology than psychiatrists 6.
Algorithmic Approach to Diagnosis
Document positive neurological signs (internal inconsistency, incongruity with disease patterns) through systematic examination including Hoover's sign, tremor entrainment testing, and assessment for give-way weakness 1.
Exclude organic pathology through appropriate investigation, recognizing that negative initial tests do not rule out neurological disease—repeat assessments and advanced imaging may be required in cases with atypical features 4.
Assess for temporal association with psychological stressors, but do not require this for diagnosis; its absence does not exclude functional neurological symptom disorder but should prompt more thorough organic work-up 4.
Evaluate symptom severity and functional impairment using dimensional assessment across multiple domains to guide treatment intensity 3.
Document episodicity and longitudinal course to distinguish first episode from recurrent patterns and track treatment response over time 3.