Functional Tremor
In the arms, ask the patient to copy a rhythmical movement made between finger/thumb using their better hand1. In the legs, ask the patient to copy foot tapping1. And in the neck, have the patient follow movements of your hand with their tongue1.
In a functional tremor, one should expect to see variable frequency (not amp) tremor that changes dramatically during externally cued rhythmic movements1. If the tremor on the other hand stops, entrains to the same rhythm, or pt has difficulty copying movement → consider functional tremor Other presentations to expect: (1)
While a functional tremor will entrain with distraction, an organic tremor will typically increase in amplitude with distraction. Entrainment can result in remission in FMD during distraction maneuvers with uninvolved limbs
| Item | Phenotype |
|---|---|
| Universal features | |
| Frequency variability | Tremor frequency changes throughout examination |
| Entrainment or full suppressability | Tremor either disappears (suppressability) or adopts the frequency of a repetitive task elsewhere (entrainment) |
| Distractibility | Tremor amplitude attenuates when attention is driven away from affected body part |
| Tonic coactiviation | Co-contraction of antagonistic muscles immediately prior to reemergence of tremor |
| Ballistic suppression | Brief arrest of tremor with performance of a ballistic movement in the opposite limb |
| Optional Features | |
| Dual task interference | Disruption in tremor frequency and amplitude when simultaneously executing a competing asks |
| Increase amplitude with weight loading | Tremor amplitude increases with increasing weight applied to limbs |
| “Whack-a-mole” sign | Spread of tremor to another body part when restrained by the examiner’s hand |
| Other functional signs or phenotypes | Give-away weakness, non-dermatomal hypoesthesia, associated functional gait disorder, functional dystonia, etc |
Many movement disorders worsen with stress/disappear with sleep → do not rely on these sx for a diagnosis