Functional Movement Disorder

Functional movement disorder is a genuine, involuntary disorder of movement (tremor, dystonia, gait disturbance, myoclonus, parkinsonism, tics, or weakness) caused by abnormal nervous system function rather than structural disease. It is diagnosed from positive clinical signs and is a common cause of neurological disability.

Functional disorders account for 5 to 10% of attendances at movement disorder clinics. The incidence is about 4 to 12 in every 100,000 people each year, and 60 to 75% of patients are women, with onset commonly in young to middle adult life.

Types. Functional tremor (commonest), dystonia, gait disorder, myoclonus and jerks, parkinsonism, tics and speech disorders.

Risk factors. Physical injury or illness at onset, adverse life events, anxiety, depression, pain, fatigue and dissociative symptoms; many have no obvious stressor.

Prognosis. About one third improve, one third stay the same and one third worsen. Early diagnosis, a clear explanation and rehabilitation improve the outcome.

Pathophysiology.

Altered attention to movement, loss of the sense of agency and abnormal predictions about movement are central, with abnormal limbic, motor and attentional network activity.

Predisposing, precipitating and perpetuating factors interact, with a mismatch between expected and actual sensory feedback.

• Abrupt onset, maximal disability early, spontaneous remissions and variable symptoms.
• Distractibility: the movement lessens when attention is diverted, and entrains (matches) with a voluntary rhythmic movement of the other limb.
• Inconsistency over time and between tasks; variable amplitude and direction; fixed postures with pain and a fixed ankle inversion.
• Gait with buckling knees, dragging leg, or excessive effort with little falling.
• Coexisting pain, fatigue, sleep disturbance, dissociation or functional seizures; may coexist with organic disease.

Red flags.

• Self-harm, severe depression or suicidal thoughts.
• Progressive or new neurological signs that are not explained by a functional disorder.
• Onset after a toxin, drug or infection that could cause an organic disorder.
• Rapid severe disability or hospitalisation with dehydration or contractures.

• Positive diagnosis from clinical signs (distractibility, entrainment, Hoover sign, give way weakness, variability and suggestibility), not from the absence of disease.
• Investigations only as needed to exclude mimics or coexisting disease: MRI, DAT SPECT in parkinsonism, copper studies in young onset, EEG in jerks.
• Neurophysiology (EMG, back averaging for jerks) for functional myoclonus.
• Assessment of mood, anxiety, dissociation, pain, sleep and past trauma.
• Video recording of the movement to show the patient and for review.

Differential diagnosis. Essential tremor, Parkinson disease, dystonia, tics, myoclonus, Wilson disease, stiff person syndrome, epilepsy, cerebellar ataxia and drug induced movement disorders.

• Explain the diagnosis positively: the symptoms are real, common, reversible and not caused by structural damage; show the signs and give written information.
• Physiotherapy and occupational therapy by therapists experienced in functional disorders: retraining automatic movement, distraction and avoiding focus on the movement.
• Psychological therapy, such as cognitive behavioural therapy, for those with psychological contributors, plus treatment of pain, sleep and fatigue.
• Stop unnecessary drugs, and avoid new dopamine blockers or sedatives.
• Treat comorbid depression and anxiety: sertraline 50 mg orally once daily, increased by 50 mg every 1 to 2 weeks as needed to 100 to 200 mg daily. Maximum 200 mg daily. Continue for at least 6 to 12 months after remission. Monitor mood and suicidal thoughts (especially under 25 years), sodium, bleeding and serotonin toxicity. Reduce the dose (or use alternate days) in hepatic impairment; no renal adjustment; avoid with monoamine oxidase inhibitors; acceptable in pregnancy and breastfeeding with specialist advice.
• Avoid repeated investigations and referrals, and avoid the wording "all in the mind".
• Multidisciplinary inpatient or intensive programmes for severe cases.

Monitoring. Review at 4 to 6 weeks, then every 3 months; track function, mood and engagement with therapy.

Referral and escalation. Neurology for diagnosis; neuropsychiatry, psychology and specialist physiotherapy; urgent psychiatric review for self-harm risk.

Special groups. Children and adolescents: family based therapy and school liaison. Pregnancy: avoid unnecessary drugs.