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Homolateral imitative synkinesis: A forgotten sign

Needham, M., Loy, C., MacAnally, L. and Morris, J. (2005) Homolateral imitative synkinesis: A forgotten sign. In: XVIII World Congress of Neurology (WCN) 2005, 5 - 11 November 2005, Sydney, Australia

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Background: While much has been written in recent years about mirror movements, where voluntary movements of the fingers on one side invoke involuntary movements of a similar character in contralateral fingers, the related phenomenon of homolateral imitative synkinesis (HIS) has been largely ignored. Here, voluntary movements of the hand invoke similar movements in the ipsilateral leg or vice versa. Both phenomena are seen in normal children but persistence into adulthood implies a pathological process.

Method and Results: We describe four patients with HIS. The first was a 71 year-old man with mild right hemiparesis associated with a small $48 Monday, November 7, 2005 Oral Platform Abstracts single melanoma metastasis in the hand area of the left primary motor cortex. Each time he raised his right arm, the right leg elevated. This amused him. It did not happen on the other side. The other patients with similar findings had, respectively: vascular dementia, right parietal meningioma and dystonia (with signal intensity changes in the basal ganglia). Mirror movements were present in some patients. Previous studies also reported a wide variety of lesion location for this sign: parietal cortex, thalamus, internal capsule, cerebellum and dorsal columns. The hallmark of HIS is loss of specificity of voluntary movements in a limb with respect to the other ipsilateral limb. Possible mechanisms include changes in cortical functional localization in response to focal lesions, loss of surround inhibition, and 'cross-talk" between adjacent fibres (as occurs in facial nerve synkinesis).

Conclusion: HIS is an interesting but neglected sign which may provide insights into plasticity and the brain's response to focal lesions.

Item Type: Conference Paper
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