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Two types of brainstem myoclonus are recognized: (1) exaggerated startle myoclonus and (2) reticular reflex myoclonus. Brainstem myoclonus is generated mainly in the reticular formation which lies close to the accessory nerve nuclei. Clinically, the muscle jerks of reticular reflex myoclonus are usually generalized with proximal more than distal and flexor more than extensor predominance. Voluntary action and sensory stimulation may increase the muscle jerks. Neurophysiologically, the first recruited muscle which jerks is the sternocleidomastoid or trapezius muscle. The myoclonic discharge then travels down the spinal cord and up the brainstem.
The patient exhibits myoclonic jerks involving her shoulders and proximal portions of her upper extremities bilaterally. The jerks occur spontaneously but are more frequent after pressure over the sternum.
Brainstem myoclonus.mp4 (MP4 13,107KB)