Myoclonus consists of involuntary, brief, sudden, shocklike muscle contractions producing visible movement. It has a variety of causes and may be focal, segmental, multifocal, or generalized. It’s cortical, subcortical, or spinal origin can be determined by neurophysiological testing. Attacks of myoclonus may be spontaneous or may be evoked by visual, auditory, or somatosensory stimuli (reflex myoclonus) or by voluntary movement (postural myoclonus, action myoclonus).
Clinical features of the internal capsule lesions. As a result of compact location of the different passways, damages of the capsulae internae include disorders of the movement, decrease in the threshold for perceiving touch, pain, and temperature and deep sensations, and the visual problems. The complete syndrome is called “the syndrome of three hemi”. Signs that may be found as a result of unilateral or bilateral involvement of the capsulae internae:
Unilateral paralysis (hemiplegia) of the opposite side of the body and contralateral III nerve palsy.
Contralateral hemihypesthesia, usually involving trunk and extremities more severely than the face.
Visual field deficit (contralateral homonymous hemianopia).
Fragmentary lesions of the anterior part of the posterior limb result in abnormalities only of the movement (contralateral hemiplegia). If damage is localized in the posterior part of the posterior limb capsulae internae the “syndrome of three hemi” is formed (contralateral homonymous hemianopia, hemihypesthesia and hemiataxia).
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