Dissociated weakness of sternocleidomastoid and trapezius muscles with lesions in the CNS

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Abstract
We describe three patients with lesions in the CNS that produced dissociated weakness of trapezius (TM) and sternocleidomastoid muscles (SCM). One patient with a right cerebral hemisphere lesion had left TM weakness and right SCM weakness. A second, with a brainstem lesion, and a third, with a high cervical cord lesion, had TM weakness with preserved SCM strength. We discuss the findings according to the known neuroanatomy.