Cortical Myoclonus, EEG-EMG, Back-Averaging, and Coherence Analysis

Abstract

This 45-year-old female patient suffers from rheumatoid arthritis since 24 years for which she has used multiple medications, including drugs that suppress the immune system. Yet, her disease has made it necessary to replace both her hip and knee joints and she has developed a severe and progressive polyneuropathy. In addition, she has heart and visual problems, and suffers from perception deafness and obstructive sleep apnea syndrome (OSAS). These medical problems have necessitated regular hospitalization for the past few years. Now, she is hospitalized again because her general condition is deteriorating and she is not recovering well from a urinary tract infection. Because involuntary movements are observed in multiple limbs when she is admitted to hospital, a neurologist is asked to examine her. The movements are classified as multifocal myoclonus and the question arises whether the myoclonic jerks originate from epileptic activity.

Glossary

Apnea

Delay of breathing.

Ataxia

Lack of muscle coordination resulting in e.g., low muscle tone (hypotonia), undershoot, or overshoot of intended position (dysmetria) and an inability to perform rapid, alternating movements (dysdiadochokinesia).

Biceps brachii

Upper arm muscle, elbow flexor.

Cerebellar ataxia

Ataxia due to dysfunctioning of the cerebellum.

Cranial nerves

Nerves emerging directly from the brain or brainstem.

Etiology

Origin, cause of a disease.

Extensor digitorum communis

Lower arm muscle, one of the wrist extensors.

First dorsal interosseus

Muscle between thumb and index finger.

Flexor carpi radialis

Lower arm muscle, one of the wrist flexors.

Hjorth

Similar to Laplacian reference.

Integrated (EMG)

Temporal summation of EMG values.

Jerk

Sudden, often uncontrolled movement.

Laplacian

Weighted average reference in which the contributions of the (surrounding) reference electrodes are weighted according to their distance to the middle input electrode.

Masseter

Muscle connecting the upper and lower jaw; its function is to aid in chewing.

Multifocal myoclonus

Brief, involuntary twitching of a muscle or a group of muscles occurring independently in different body parts.

Noncephalic

Not related to the head, here, a reference electrode that is not attached to the scalp but, e.g., to the sternum.

Obstructive sleep apnea syndrome

Sleep disorder characterized by regular cessation of breathing caused by a blockage of the airway (e.g. by the tongue or other tissues).

Orbicularis oculi

Muscle around the eye; its function is to close the eyelid.

Perception deafness

Hearing loss due to a dysfunction of the inner ear or hearing pathways.

Polyneuropathy

Neuropathy (see Glossary Chap. 2) affecting multiple nerves.

Rectified (EMG)

Absolute value of the EMG, i.e. positive values remain positive and negative values become positive (by removing the minus sign).

Rheumatoid arthritis

Systemic inflammatory autoimmune disease affecting many tissues and organs but mostly the joints that contain a lubricating (synovial) fluid.

Smoothed (EMG)

Running average of EMG amplitude, sometimes the weights are not the same for every EMG value. Smoothing is a form of low-pass filtering.

Sternocleidomastoid

Muscle in the frontal part of the neck; its function is to rotate and flex the head.