<style> .reveal { font-size:24px; } </style> ## 21 Neurologic Causes of W and Paralysis --- Normal :muscle: function involves integrated muscle activity that is modulated by the activity of the cerebral cortex, basal ganglia, cerebellum, red nucleus, brainstem reticular formation, lateral vestibular nucleus, and spinal cord. --- * :muscle: system dysfunction leads to W or paralysis, discussed in this chapter, or to ataxia or abnormal movements. * W is a reduction in the power that can be exerted by one or more :muscle:. * It must be distinguished from * increased fatigability * limitation in function due to pain or articular stiffness * impaired :muscle: activity because severe proprioceptive sensory loss prevents adequate feedback information about the direction and power of movements. --- * It is also distinct from * **bradykinesia** (in which increased time is required for full power to be exerted) and * **apraxia**, a disorder of planning and initiating a skilled or learned movement unrelated to a significant :muscle: or sensory deficit. --- **Paralysis**/ **“-plegia”** :point_right: :muscle: cannot be contracted at all **Paresis** :point_right: less severe W. **“hemi-”** :point_right: one-half of the body, **“para-”** :point_right: both legs **“quadri-”** :point_right: four limbs. --- The distribution of W helps to localize the underlying lesion. **UMN W** :point_right: extensors and abductors of the upper limb and the flexors of the lower limb. **LMN W** :point_right: depends on whether involvement is at the level of the anterior horn cells, nerve root, limb plexus, or peripheral nerve'' **Myopathic W** :point_right: most marked in **proximal :muscle:**. --- **Tone** is the **resistance of a muscle to passive stretch**. * **Spasticity** * velocity-dependent, has a sudden release after reaching a maximum (the “clasp-knife” phenomenon). predominantly affects the antigravity :muscle: * **Rigidity** * present throughout the ROM (a “lead pipe” or “plastic” stiffness) / affects flexors and extensors equally * cogwheel quality, enhanced by voluntary movement of the contralateral limb (reinforcement) * extrapyramidal disorders, such as Parkinson’s disease. * **Paratonia** (or gegenhalten) https://www.youtube.com/watch?v=Z-NjgIPbuEU * present throughout the ROM / affects flexors and extensors equally * usually results from disease of the frontal lobes. --- * **DTR** usually increased with UMN lesions * may be decreased or absent for a variable period immediately after onset of an acute lesion. * preserved in patients with myopathic W except in advanced stages  ---  ==FIGURE 21-1 The corticospinal(pyramidal) and bulbospinal(extrapyramidal) UMN pathways.== ---  ==FIGURE 21-2 LMN are divided into α and γ types.== * A tap on a tendon stretches muscle spindles and activates the primary spindle afferent neurons. These neurons stimulate the α motor neurons in the spinal cord, producing a brief muscle contraction, which is the familiar tendon reflex. ---  ---  --- ***PATHOGENESIS*** ==UMN Weakness== * In general, ==distal muscle groups== are affected more severely than proximal ones, and axial movements are spared unless the lesion is severe and bilateral. * ==Spasticity== is typical but may not be present acutely. * ==Rapid repetitive movements are slowed and coarse==, but normal rhythmicity is maintained. * Bilateral corticobulbar lesions produce a ==pseudobulbar palsy== * Electromyogram (EMG) shows that with W of the UMN type, :muscle: units have a ==diminished maximal discharge frequency== ---  --- ==LMN Weakness== * When a :muscle: unit becomes diseased, especially in anterior horn cell diseases, it may discharge spontaneously, producing ==fasciculations== * EMG: delayed or reduced recruitment of :muscle: units --- ==NMJ weakness disorders== eg. MG, Lambert-eaton * W of variable degree and distribution. * Strength is influenced by preceding activity of the affected muscle. * MG : Fatigable weakness ==Myopathic W== eg. muscular dystrophies, inflammatory myopathies etc * produced by a decrease in the number or contractile force of muscle fibers activated within motor units. * EMG: size of each MUAP is decreased ==Psychogenic W== may occur without a recognizable organic basis. ---  --- **Hemiparesis** results from an ==UMN lesion above the midcervical spinal cord== * The presence of other neurologic deficits helps localize the lesion. * language disorders,homonymous VF defects etc * A “pure :muscle:” hemiparesis of the face, arm, and leg * due to a small, discrete lesion in the posterior limb of the internal capsule, cerebral peduncle in the midbrain, or upper pons.  * The absence of cranial nerve signs or facial W suggests that a hemiparesis is due to a lesion in the high cervical spinal cord, especially if associated with the Brown-Séquard syndrome. --- ==Pure motor hemiparesis==  --- **Paraparesis** * ==Acute== paraparesis is caused most commonly by an ==intraspinal== lesion, but its spinal origin may not be recognized initially if the legs are flaccid and areflexic. * cauda equina syndrome, for example, after trauma to the low back, a midline disk herniation, or an intraspinal tumor. The sphincters are commonly affected. * If ==hemispheric signs== are present, a parasagittal meningioma or chronic hydrocephalus is likely. ---  --- **Quadriparesis or Generalized Weakness** ==In obtunded patients, evaluation begins with a CT scan of the brain.== * Onset over minutes : UMN disorders (anoxia, hypotension etc) or muscle (electrolyte disturbances, certain inborn errors etc) * Onset over hours to weeks : UMN, LMN disorders such as Guillain-Barré syndrome * Develop over weeks to years : chronic myelopathies, multiple sclerosis etc --- **Monoparesis** **ACUTE MONOPARESIS** * distal/UMN type/not associated with sensory impairment or pain, focal cortical ischemia is likely * Sensory loss and pain usually accompany acute LMN W **SUBACUTE OR CHRONIC MONOPARESIS** * W and atrophy that develop over weeks or months are usually of LMN origin. --- **Proximal W** * Myopathy often produces symmetric weakness of the pelvic or shoulder girdle :muscle:. * Diseases of the NMJ, such as MG, may present with symmetric proximal W often associated with ptosis, diplopia, or bulbar W and fluctuating in severity during the day. * In anterior horn cell disease, proximal W is usually asymmetric, may be symmetric if familial. --- **W in a Restricted Distribution** W may not fit any of these patterns, being limited, for example, to the extraocular, hemifacial, bulbar, or respiratory :muscle:. * Bilateral facial palsy with areflexia suggests Guillain-Barré syndrome. ---  ==GBS paralysis affects the muscles of respiration, possibly leading to death due to respiratory failure.== ---