LAUSR

Isolated position-specific or task-specific tremors (TST) are subtypes of the essential tremor (ET) which are characterized by task-specific tremor that occurs with a specific task [1, 2]. Primary writing tremor is the most frequent example of such a tremor and arises in specialized fields of motor performance. Other examples include specific tremors in musicians and athletes. Given its rarity, TST pathophysiology is yet unknown. We describe a case of a sensory trick associated with TST which expands the clinical phenotype of TST syndromes. The patient is a 66-year-old, right-handed woman of Italian origin. Her parents were unrelated and did not suffer from any neurological disorders. She is in good health, not requiring any medications on long-term basis. During the last 2 years, she has developed mild action tremor in the left hand, which has a progressive course. The tremor gradually became of a very wide amplitude and was induced especially by the task of holding a solid object, such as a dish or a tray at a horizontal extension. The sensory trick is characterized by sensory stimulation by touching the left wrist with the right hand. There was no evidence of mirror movements or overflow. The remaining neurological examination was normal. She was treated with clonazepam, alprazolam, duloxetina, propranolol, and escitalopram without any benefit. Propranolol was poorly tolerated by the patient as it induced the sense of ‘‘frost’’ in the left hand. Basic investigations including MRI and standard EEG were entirely normal. Multiple simultaneous electromyography recordings (mapping) were performed and showed the alternate contraction of agonists and antagonists without sustained simultaneous contractions, thus confirming the diagnosis of TST. A treatment with botulinum toxin injection in the pronator teres muscle was proposed, but the patient did not consent to treatment. Sensory tricks are forms of tactile stimulations which lead to transient improvements in posture or spasm amplitude in cervical or other forms of dystonia. The presence of alleviating maneuvers, as sensory tricks or gestes antagonistes, is considered a supporting evidence for the diagnosis of dystonia. They are proposed as additional clinical signs due for the diagnosis of dystonia, particularly when the full-house phenomenology is not observed [3]. In addition, sensory tricks do not improve non-dystonic essential head tremor, and they are proposed as an important criterion for the differential diagnosis between dystonia and ET [4]. The phenomenon of sensory tricks has been described as a clinical hallmark which can detect dystonic movements in patients affected by other movement disorders as tics or tremor. In the syndrome of tardive tremor, the presence of a sensory trick has been associated with the diagnosis of Electronic supplementary material The online version of this article (doi:10.1007/s10072-017-2913-x) contains supplementary material, which is available to authorized users.