Motor FND
The motor subtype of functional neurological disorder is characterised by a wide range of symptoms, including limb weakness, gait disturbances, tremor, dystonia, tics and jerks. Due to the considerable heterogeneity of symptoms, treatment should always be individually tailored to the patient, taking into careful consideration the type of symptom, any associated disorders and personality preferences.
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Tremor refers to uncontrollable shaking of a body part (e.g. hands, feet, head, etc.). It is often confused with Parkinson's disease or Essential Tremor. The tremor is uncontrollable by the patient and is not caused by organic damage but by malfunctioning of the central nervous system. Tremor may appear and disappear during the day, and may also change the rate and of rhythm.
Features
The tremor takes on the rhythm of dynamic movements performed with another part of the body
Pause followed by rapid movement of the other limb
Variability of frequency, amplitude
Tonic contraction at the beginning
Increase in amplitude with weighting
Consistent tremor between two limbs
Whack-a-mole sign (holding back a tremor causes tremors in another part of the body)
Clinical tests
Clinical neurophysiological measurements can quantify the rhythm of dynamic movements performed with the other body part, pauses with rapid movement of the other limb, variability, tonic contraction at the onset, increase in amplitude with weights and coherence between limbs
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(Fixed) dystonia is characterised by abnormal body positions (e.g. twisted fingers, clenched fist, ankle pointing downwards or inwards) that are difficult or almost impossible to change. It can be temporary (spasm) or chronic (fixed dystonia).
Features
Certain dystonic patterns such as fixed dystonia or pulling the lip to one side
Clinical tests
Recovery of the normal blink reflex
Normal plasticity with pairwise associative conditioning
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When we talk about tics, we are talking about a series of repetitive, rapid, sudden movements or sounds that are not rhythmic. If they involve more than one movement and, if they involve a combination of movements and sounds, we are talking about complex tics. Tics are also characteristic of other neurological conditions such as Tourette's syndrome.
Features
Lack of need
Lack of voluntary control
Clinical tests
Normalen Bereitschaftspotential
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Gait disorders refer to problems with walking where there may be abnormal movement or body position. As with other functional neurological disorders, movement and is involuntary. Types of gait include: squatting gait, abnormally bent knee, slow gait (walking on ice), wobbling gait and hyperkinetic gait.
Features
Specific movement patterns, including knee flexion, dragging of the monopleg, asthasia-abasia, excessive slowness and atypical limp
Better balance than expected; balance is further improved with distraction techniques
No falls/controlled falls/falling against a support
Chair test (legs can be used to move the chair better than to walk)
Clinical tests
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Most people have experienced bedtime twitching or random body 'jolts', but these are normal. On the other hand, myoclonus (the technical term for twitching) - a jerky and shock-like movement that belongs to the functional motor neurological disorders - severely impairs the quality of life of patients.
Features
Variability and longevity of movement
Complex movement
Appearance of abandonment
Long and variable latency of the stimuli causing the jerks
The jerk when the whale hammer stops before contact
Clinical tests
Long bursts of electromyography
Presence of Bereitschaftspotential (readiness potential) before the jerk
Stimulus-triggered jerks: long and variable latency
Diagnosing
According to the DSM-5, mFND is diagnosed when diagnostic features are present on examination:
instability (e.g. changes in frequency/amplitude/remittance/worsening of motor symptoms) and,
incongruence (incongruence with other neurological disorders), focusing on positive physiological features such as Hoover sign (Perez et al., 2021).
Positive signs indicating functional weakness of the limb, functional sensory and of gait impairment are:
weakness of the easing/sitting,
gliding without pronation (i.e. inward movement of the foot to optimally distribute the force of impact on the ground during running),
cocontraction (simultaneous contraction of two muscles),
Hoover's sign,
hip abductor sign,
Spinal Injuries Centre test and
Sternocleidomastoid weakness with hemiparesis.
The possibility of functional tremor can be considered when it has a variable frequency (and not amplitude!) that changes dramatically during external instructions of rhythmic movements. We speak of functional hand tremor when the patient has difficulty copying the rhythmic movement between the fingers and thumb of the better hand, when the tremor in the other hand stops or matches the same rhythm. For a leg tremor, have the patient try to copy the tapping of the feet, and for a neck tremor, have the patient follow the movement of your hands with your tongue (Bennet et al., 2021).
Functional dystonia is usually manifested by fixed abnormal posture and includes inverted/plantar ankle flexion or toe flexion. Clinically, it may be comorbid with complex regional pain syndrome whose motor and sensory features mimic those of FND (Bennet et al., 2021). Another common type of functional dystonia can be identified by a deviation of the jaw to one side, where the lip curls downwards (or sometimes upwards), giving the appearance of facial weakness.
Treatment
Treatment of functional motor disorders is individualised and tailored to the severity and variability of symptoms, while taking into account comorbid disorders and/or symptoms. The multidisciplinary team may consist of a neurologist, physiotherapist, (neuro)psychologist, psychiatrist, occupational and speech therapist and social worker. Patients often benefit from targeted interventions, either by a psychologist or a physiotherapist. The aim is to regain control of movement, identify triggers and maintainers, and make behavioural changes that have a positive impact on the expression of symptoms. The most evidence in the scientific literature of its effectiveness in treatment is provided by specialist physiotherapy, which is based on the assumption that abnormal movement patterns (which develop outside the patient's control) accompanied by an increased level of attention to symptoms can be retrained. Thus, in addition to physiotherapy, psychological treatments that address beliefs about the disorder and are based on modifying maladaptive behaviour are also useful (Gilmour et al., 2020).Newer approaches such as transcranial magnetic stimulation, hypnosis and electromyographic biofeedback are also increasingly being used as adjuncts to treatment (Gilmour et al., 2020).
Key points
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Onset of symptoms occurs on average between 39-49 years of age and is predominant in the female sex.
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The onset of symptoms is sudden in most cases (>50%).
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Often occur in temporal proximity to the onset of symptoms and are often easily identified (48%-80%): injuries, accidents, surgical procedures, residual medical interventions and emotionally charged events.
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Comorbidity with pain, fatigue, dizziness, gastrointestinal complaints, sleep disturbances, cognitive symptoms
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Periods of deterioration and improvement, including spontaneous periods of remission.
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Comorbidities with depression [35%-42%], generalised anxiety disorder [7%-23%], panic disorder [3%-36%], post-traumatic stress disorder [0%-24%], somatisation disorder [22%-27%], and personality disorders [20%-30%]) are common in adults. In children, it is comorbid with mood disorders (9%-16%) and anxiety disorders (18%-100%).
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Childhood maltreatment (abuse and neglect) is often identified, but not everywhere.
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American Psychiatric Association. (2013). Diagnostic and statistical manual of mental disorders (5th ed.). Arlington, VA: American Psychiatric Publishing.
Apazoglou, K., Mazzola, V., Wegrzyk, J., Polara, G. F., and Aybek, S. (2017). Biological and perceived stress and motor functional neurological disorders. Psychoneuroendocrinology, 85, 142-150.
Aybek, S., and Perez, D. L. (2022). Diagnosis and management of functional neurological disorder. bmj, 376.
Bennett, K., Diamond, C., Hoeritzauer, I., Gardiner, P., McWhirter, L., Carson, A., and Stone, J. (2021). A practical review of functional neurological disorder (FND) for the general physician. Clinical Medicine, 21(1), 28.
Gilmour, G. S., Nielsen, G., Teodoro, T., Yogarajah, M., Coebergh, J. A., Dilley, M. D., ... and Edwards, M. J. (2020). Management of functional neurological disorder. Journal of Neurology, 267, 2164-2172.
O'connell, N., Watson, G., Grey, C., Pastena, R., McKeown, K., and David, A. S. (2020). Outpatient CBT for motor functional neurological disorder and other neuropsychiatric conditions: a retrospective case comparison. The Journal of Neuropsychiatry and Clinical Neurosciences, 32(1), 58-66.
Perez, D. L., Aybek, S., Popkirov, S., Kozlowska, K., Stephen, C. D., Anderson, J., ... and American Neuropsychiatric Association Committee for Research. (2021). A review and expert opinion on the neuropsychiatric assessment of motor functional neurological disorders. The Journal of neuropsychiatry and clinical neurosciences, 33(1), 14-26.
Perez, D. L., Edwards, M. J., Nielsen, G., Kozlowska, K., Hallett, M., and LaFrance Jr, W. C. (2021). Decade of progress and motor functional neurological disorder: continuing the momentum. Journal of Neurology, Neurosurgery & Psychiatry, 92(6), 668-677.
Saxena, A., Godena, E., Maggio, J., and Perez, D. L. (2020). Towards an outpatient model of care for motor functional neurological disorders: a neuropsychiatric perspective. Neuropsychiatric Disease and Treatment, 2119-2134.