What are the diagnostic criteria for functional neurological disorder (FND)?

Diagnostic Criteria for Functional Neurological Disorder

Functional Neurological Disorder (FND) is diagnosed by identifying positive clinical signs of internal inconsistency and incompatibility with recognized neurological diseases, not by exclusion of other conditions. 1

Mandatory Core Criteria

The diagnosis requires all of the following elements 1:

• One or more neurological symptoms affecting voluntary motor or sensory function 1
• Clinical examination findings demonstrating incompatibility with known neurological or medical diseases 1, 2
• Clinically significant distress or functional impairment related to the symptoms 1
• Symptoms not better explained by another neurological or medical condition 1

Positive Clinical Signs (The Foundation of Diagnosis)

Internal Inconsistency Features

These are the hallmark diagnostic signs 1:

• Symptom variability during distraction – symptoms resolve or diminish when the patient's attention is diverted during spontaneous conversation or automatic tasks 1
• Suggestibility – symptoms become more prominent when discussed or examined 1
• Disproportionate severity – observed deficits far exceed what would be expected from any documented injury or lesion location 1

Movement Pattern Abnormalities

• Inefficient movement patterns – excessive struggle behaviors including over-mouthing, frequent eye blinking, facial contortions, exaggerated breathing effort, neck/shoulder tension, and frequent postural shifts 1
• Paradoxical fatigue pattern – in reported weakness, fatigue occurs in the direction of muscle hyper-function rather than hypo-function 1

Specific Sign for Functional Seizures

• Eyes closed during an event distinguishes functional (non-epileptic) seizures from epileptic seizures 1

Symptom Subtypes That Can Be Coded

Motor manifestations 1, 2:

• Weakness or paralysis
• Movement disorders (tremor, jerks, dystonia)
• Gait abnormalities

Sensory manifestations 1, 2:

• Altered sensation, numbness, pain

Seizure-type manifestations 1, 2:

• Dissociative (non-epileptic) seizures

Speech and communication disturbances 1:

• Functional dysphonia, dysarthria, stuttering, functional foreign-accent syndrome

Other manifestations 1:

• Swallowing disturbances (functional dysphagia)
• Cognitive complaints (memory, concentration, word-finding problems)
• Functional cough and laryngeal hypersensitivity syndrome

Essential Historical Elements for Diagnosis

Capture these specific details 1:

• Onset characteristics – how and when symptoms began and the patient's perceived cause 1
• Temporal pattern – constant versus intermittent, aggravating/relieving factors, any periods of complete resolution 1
• Previous medical encounters – information conveyed by other providers and outcomes of prior treatments 1
• Functional impact on daily activities, work, and relationships 1
• Precipitating physical triggers – recent infection, injury, head trauma, or surgery 1

Critical Diagnostic Pitfalls to Avoid

The absence of psychological stressors or psychiatric comorbidity does NOT exclude FND 1. This is a common and damaging misconception. Key clarifications include:

• Symptoms often arise after physical triggers (infection, injury, head trauma) rather than psychological trauma 1
• Repeatedly questioning patients about trauma when none is reported damages the therapeutic relationship 1
• Lack of identifiable adversity or distress should not be used as evidence against a functional diagnosis 1
• Diagnosing by exclusion alone is incorrect; FND requires the presence of positive clinical features 1, 3, 4

Co-existence with Structural Disease

FND can co-occur with structural neurological pathology 1. The presence of organic findings does not rule out a functional overlay, which is identified through positive clinical features distinguishing functional from structural elements 1. This requires careful examination to identify which symptoms are functional versus structural.

Diagnostic Certainty

Ideally, identify multiple positive features consistent with FND for the diagnosis to be made with a high degree of certainty 4. The more robustly present positive signs you identify, the more confident the diagnosis.

Biopsychosocial Context (Not Required for Diagnosis but Aids Understanding)

The three-factor model helps conceptualize perpetuating factors 1, 5:

• Predisposing vulnerabilities – biological (genetic factors, prior functional symptoms, traumatic brain injury), psychological (neuroticism, perfectionism, low self-esteem), or social (adverse life events, chronic stress) 1
• Precipitating mechanisms – physical triggers are often more relevant than psychological stressors 1
• Perpetuating factors – self-directed attention to symptoms, avoidance behaviors, abnormal movement patterns 1