Trapezius and Sternocleidomastoid Weakness | Signs - MedSchool
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Trapezius and Sternocleidomastoid Weakness

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Accessory Nerve Muscular Weakness

    • How to Elicit

    • Sternocleidomastoid - ask the patient to turn their head against resistance.A CN XI lesion may cause weakness on head turning away from side of lesion
    • Trapezius - ask the patient to shrug their shoulders against resistance.An CN XI lesion may cause weakness in shoulder elevation on ipsilateral side
    • Causes of Accessory Nerve Muscular Weakness

    • Upper motor neuron  brainstem or cervical spinal cord
    • Lower motor neuron - accessory (XI) weakness
    • Interpretation

    • Isolated Trapezius WeaknessVentral brainstem, lower cervical spinal cord or lower accessory nerve lesion
    • Isolated Sternocleidomastoid WeaknessBrainstem or upper cervical lesion
    • Weakness of Trapezius and Contralateral SternocleidomastoidUpper motor neurone lesion on the side of the SCM weakness, above the accessory nucleus
    • Weakness of Ipsilateral TrapeziusContralateral brainstem, ipsilateral high cervical cord, or accessory nerve lesion
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