ABSTRACT
DISCUSSION This patient’s clinical and electrophysiological findings are indicative of a psychogenic tremor. Such tremors can be difficult to diagnose, as the clinical presentation alone with an ongoing rhythmic hand tremor between 4 and 7 Hz often does not allow a distinction from organic tremors. Being mainly postural and action tremors they often remain at rest, especially when the patient cannot relax completely. 2 The history and specific clinical tests offer some clues that a tremor is psychogenic. While organic tremors typically develop gradually over time, the vast majority of patients with psychogenic tremor report a sudden onset, often in connection with minor trauma. 3 Previous or other somatizations and psychogenic symptoms, such as the accompanying paresis in the present case, can be another hint but may be misleading. One typical clinical sign of a psychogenic tremor is distractibility: demanding mental or motor tasks will reduce the tremor 3 and make it more variable. 4
Another well-established clinical characteristic of a psychogenic tremor is the ‘coactivation sign’ 2 designating a constant isometric activation of antagonistic muscles. This continuous increase in motor neuron excitability may lead to an enhancement of physiological oscillatory mechanisms (e.g. clonus). 2,5 It can be assessed clinically, similar to testing for rigidity, and was extremely strong in the present patient (see second segment of video, Case 45 ). While organic tremors typically occur independently (non-coherently) in different limbs, voluntary rhythmic movements are usually synchronized or coupled (coherent) between different extremities. 1 Provided that the psychogenic tremor relies on similar mechanisms to voluntary movements this interlimb coherence could be one way to distinguish it from an organic tremor. Indeed, when looking at the relation between the tremor in different limbs or between a voluntarily maintained
rhythm of the one hand with the tremor in the other hand (entrainment test), they were often found to be coupled. 1,5 However, in about one-half of patients with psychogenic tremors the rhythm in both limbs was independent, as in organic tremors. 5 In those cases the suggested mechanism of enhanced non-voluntary but physiological oscillatory mechanisms (e.g. clonus) seems to be more important.
