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Upper Motor Neuron Weakness



    • Signs of Upper Motor Neuron Weakness

    • Minimal muscle wasting
    • Spasticity (clasp-knife rigidity) - velocity-dependent increase in tone
    • Clonus - rhythmic contractions in response to a sudden stimulus, e.g. sudden ankle dorsiflexion
    • Reduced power
    • Hyperreflexia
    • Upgoing plantar reflex
    • Significance

    • The presence of upper motor neuron weakness suggests a lesion within the central nervous system, involving the cerebrum, brainstem or spinal cord.
    • Causes of Upper Motor Neuron Weakness

    • Ischaemia - ischaemic stroke, spinal cord infart
    • Haemorrhage - subarachnoid haemorrhage, intracerebral haemorrhage
    • Traumatic brain injury
    • Tumour - astrocytoma, meningioma, brain metastases, spinal cord neoplasia
    • Infection - encephalitis, PML, brain abscess
    • Demyelination - ADEM, multiple sclerosis
    • Hereditary spastic paraparesis
    • Idiopathic transverse myelitis
    • CNS vasculitis
    • Sarcoidosis
    • Syringomyelia
    • Prion disease
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