Holmes' or functional tremor?

Abstract

Objective: Holmes tremor is a rare kind of hyperkinetic movement disorder, clinically characterized by irregular, monolateral, high-amplitude jerks, sharing a quite similar frequency with those observed in Parkinson's disease; its generation likely relies on a combined involvement of cerebello-thalamic and nigrostriatal pathways.

Methods: We report the case of a man with a combined resting-postural-kinetic tremor. Neuroimaging revealed an intracranial dermoid cyst at the right pontocerebellar angle with brainstem dislocation. We performed an extensive electrophysiological assessment from the extensor digitorum communis (EDC) and flexor carpi radialis (FCR) muscles.

Results: Both the spontaneous variability of tremor frequency and frequency entrainment argued against an organic aetiology. Polymyography revealed: 1) a paradoxical increase of tremor amplitude with mass loading; 2) jerks' synchronization between antagonistic muscles during voluntary contralateral motor performances; 3) tremor inhibition while asking the patient to make a ballistic movement.

Conclusions: We suggest a complete psychogenic genesis or, at least in part, a possible co-existence of a rubral tremor with functional traits.

Significance: Here, we propose a simple and fast test battery for an early diagnosis of functional tremor. Our results prompt further studies to re-define electrodiagnostic criteria in hyperkinetic movement disorders, possibly updating the floating border between organic and psychogenic disease.

Keywords: Functional tremor; Holmes tremor; Neurophysiology; Psychogenic tremor; Rubral tremor; Surface polymyography.

Fig. 1

Neuroimaging and surface electromyography. A – MRI scan revealed an intracranial dermoid cyst causing severe midbrain and pons dislocation. B – Surface EMG was evaluated in six different conditions: at rest or with arms outstretched at shoulder level (top traces), during mass loading or contralateral movements (at the middle), during ballistic movements or making a finger tapping by synchronizing contralateral movements with a 3 Hz metronome (bottom traces). Note the different frequency between postural and rest jerks, the increase of tremor amplitude with mass loading, as well as jerks’ synchronization during voluntary contralateral movements. Both tremor inhibition and co-activation sign (black arrow) appeared while asking the patient to make a ballistic movement (R = right; L = left; EDC = extensor digitorum communis; FCR = flexor carpi radialis).