Chapter 023. Weakness and Paralysis (Part 4) pps

Weakness and Paralysis Part 4 Hemiparesis Hemiparesis results from an upper motor neuron lesion above the midcervical spinal cord; most such lesions are above the foramen magnum.. The a

Chapter 023 Weakness and Paralysis

(Part 4)

Hemiparesis

Hemiparesis results from an upper motor neuron lesion above the midcervical spinal cord; most such lesions are above the foramen magnum The presence of other neurologic deficits helps to localize the lesion Thus, language disorders, cortical sensory disturbances, cognitive abnormalities, disorders of visual-spatial integration, apraxia, or seizures point to a cortical lesion Homonymous visual field defects reflect either a cortical or a subcortical hemispheric lesion A "pure motor" hemiparesis of the face, arm, or leg is often due to a small, discrete lesion in the posterior limb of the internal capsule, cerebral peduncle, or upper pons Some brainstem lesions produce "crossed paralyses," consisting of ipsilateral cranial nerve signs and contralateral hemiparesis (Chap 364) The absence of cranial nerve signs or facial weakness suggests that a hemiparesis is due to a lesion in the high cervical spinal cord, especially if

associated with ipsilateral loss of proprioception and contralateral loss of pain and temperature sense (the Brown-Séquard syndrome)

Acute or episodic hemiparesis usually results from ischemic or

hemorrhagic stroke, but may also relate to hemorrhage occurring into brain tumors

or as a result of trauma; other causes include a focal structural lesion or inflammatory process as in multiple sclerosis, abscess, or sarcoidosis Evaluation begins immediately with a CT scan of the brain (Fig 23-3) and laboratory studies

If the CT is normal and an ischemic stroke is unlikely, MRI of the brain or cervical spine is performed

Figure 23-3

An algorithm for the initial workup of a patient with weakness EMG, electromyography; LMN, lower motor neuron; NCS, nerve conduction studies;

UMN, upper motor neuronSubacute hemiparesis that evolves over days or weeks

has an extensive differential diagnosis A common cause is subdural hematoma, especially in elderly or anticoagulated patients, even when there is no history of trauma Infectious possibilities include cerebral abscess, fungal granuloma or meningitis, and parasitic infection Weakness from primary and metastatic neoplasms may evolve over days to weeks AIDS may present with subacute hemiparesis due to toxoplasmosis or primary CNS lymphoma Noninfectious

inflammatory processes, such as multiple sclerosis or, less commonly, sarcoidosis, merit consideration If the brain MRI is normal and there are no cortical and hemispheric signs, MRI of the cervical spine should be undertaken

Chronic hemiparesis that evolves over months is usually due to a neoplasm

or vascular malformation, a chronic subdural hematoma, or a degenerative disease

If an MRI of the brain is normal, the possibility of a foramen magnum or high cervical spinal cord lesion should be considered

Paraparesis

An intraspinal lesion at or below the upper thoracic spinal cord level is most commonly responsible, but a paraparesis may also result from lesions at other locations that disturb upper motor neurons (especially parasagittal intracranial lesions) and lower motor neurons [anterior horn cell disorders, cauda equina syndromes due to involvement of nerve roots derived from the lower spinal cord (Chap 372), and peripheral neuropathies]

Acute paraparesis may not be recognized as due to spinal cord disease at an

early stage if the legs are flaccid and areflexic Usually, however, there is sensory loss in the legs with an upper level on the trunk; a dissociated sensory loss suggestive of a central cord syndrome; or exaggerated stretch reflexes in the legs with normal reflexes in the arms It is important to image the spinal cord (Fig 23-3) Compressive lesions (particularly epidural tumor, abscess, or hematoma, but

also a prolapsed intervertebral disk and vertebral involvement by malignancy or infection), spinal cord infarction (proprioception is usually spared), an arteriovenous fistula or other vascular anomaly, and transverse myelitis, are among the possible causes (Chap 372)

Diseases of the cerebral hemispheres that produce acute paraparesis include anterior cerebral artery ischemia (shoulder shrug is also affected), superior sagittal sinus or cortical venous thrombosis, and acute hydrocephalus If upper motor neuron signs are associated with drowsiness, confusion, seizures, or other hemispheric signs, MRI of the brain should be undertaken

Paraparesis may result from a cauda equina syndrome, for example, following trauma to the low back, a midline disk herniation, or an intraspinal tumor; although sphincters are affected, hip flexion is often spared, as is sensation over the anterolateral thighs Rarely, paraparesis is caused by a rapidly evolving anterior horn cell disease (such as poliovirus or West Nile virus infection), peripheral neuropathy (such as Guillain-Barré syndrome; Chap 380) or myopathy (Chap 382) In such cases, electrophysiologic studies are diagnostically helpful and refocus the subsequent evaluation

Subacute or chronic paraparesis with spasticity is caused by upper motor

neuron disease When there is associated lower-limb sensory loss and sphincter involvement, a chronic spinal cord disorder is likely (Chap 372) If an MRI of the

spinal cord is normal, MRI of the brain may be indicated If hemispheric signs are present, a parasagittal meningioma or chronic hydrocephalus is likely and MRI of the brain is the initial test In the rare situation in which a longstanding paraparesis has a lower motor neuron or myopathic etiology, the localization is usually suspected on clinical grounds by the absence of spasticity and confirmed by EMG and nerve conduction tests