functional neurological symptom disorder

**DSM-5(-TR) criteria** - One or more symptoms of altered voluntary motor or sensory function. - Clinical findings provide evidence of incompatibility between the symptom and recognized neurological or medical conditions. - The symptom is not better explained by another medical or mental disorder. - The symptom causes clinically significant distress or functional impairment, or warrants medical evaluation. - DSM-5 removed the requirement for an identifiable psychological stressor and the requirement that symptoms be "not feigned," because both are hard to assess reliably. Feigning is still excluded clinically (malingering and factitious disorder are separate diagnoses). - Specifiers: symptom type (weakness/paralysis, abnormal movement, swallowing, speech, attacks/seizures [psychogenic nonepileptic seizures, PNES], anesthesia/sensory loss, special sensory, mixed), acute (<6 months) vs persistent (≥6 months), and with or without psychological stressor.

**Pathophysiology** - The cause is not fully understood. It is a disorder of brain network function rather than structure. - Neuroimaging studies suggest altered limbic activity (amygdala), altered motor planning and sense of agency (temporoparietal junction), and abnormal attention and prediction processing. - Historical and psychodynamic models describe unconscious conversion of psychological conflict into physical symptoms. Primary gain is reduced anxiety or conflict. Secondary gain is external benefit from the illness. - Risk factors: female sex (about 2–3:1), childhood abuse or neglect, recent stressors or trauma, comorbid anxiety, depression, PTSD or dissociation, and coexisting neurologic disease.

**Clinical features and positive signs** - Diagnosis rests on positive signs of internal inconsistency, not on exclusion alone. - **Hoover sign:** In functional leg weakness, hip extension weakness returns to normal strength when the patient flexes the contralateral hip against resistance. - **Hip abductor sign.** - **Give-way (collapsing) weakness.** - **Drift without pronation:** Arm drift occurs without pronation. - **Midline splitting of vibration sense.** - **Tunnel vision:** The visual field does not widen with distance. - **Functional gait:** Dramatic lurching with a "wastebasket" quality but rare falls, or a dragging monoplegic gait. - **Functional tremor:** Entrainable and distractible, with variable frequency and a tendency to stop when the patient is distracted. - **PNES:** Features include long duration (>2 min), eyes closed during the event, side-to-side head movement, pelvic thrusting, asynchronous movements, fluctuating course, ictal crying and recall of the event. Features that are not seen include postictal confusion, tongue biting (lateral tongue biting suggests a true seizure), incontinence and elevated serum prolactin. Video-EEG monitoring is the gold standard. - La belle indifférence (inappropriate lack of concern) is classically described, but it is non-specific and not diagnostic.

**Differential diagnosis** - Neurologic disease: MS, myasthenia gravis, stroke, epilepsy, Guillain-Barré syndrome. - Other psychiatric diagnoses: somatic symptom disorder (excessive thoughts and behaviors about symptoms, not necessarily neurologic deficits), illness anxiety disorder, factitious disorder (intentional falsification without clear external reward), and malingering (intentional production for external gain such as money or avoiding legal consequences). - Key board distinction: in conversion disorder, symptoms are unintentional and unconscious. In factitious disorder and malingering, they are conscious and intentional. Factitious disorder is driven by the wish to assume the sick role, and malingering by external incentives.

**Management** - Make a clear, positive diagnosis, explain it as real and not "faked," and reassure that it is potentially reversible. - Avoid repeated unnecessary testing and invasive procedures. - Physiotherapy (key for motor symptoms), CBT, and treatment of comorbid depression and anxiety. - Psychotherapy for PNES. - Prognosis is better with acute onset, a clear stressor, younger age, and early diagnosis. Chronic symptoms, personality disorder and prolonged disability predict a worse outcome.

**High-yield exam pearls** - Classic vignette: a young woman develops sudden blindness, paralysis or aphonia after an emotional stressor, with normal exam findings, reflexes, imaging and EEG, and signs such as the Hoover sign. - Unconscious production is the key distinction from malingering and factitious disorder. - Do not call it "hysteria" or "pseudoseizures." Preferred terms are functional or psychogenic nonepileptic seizures.