Myoclonus

Diagnosis

Determining the cause of a patient's myoclonus can involve a lengthy elimination process. Doctors usually begin by taking a full history including a description of the myoclonus, other neurological problems, any history of seizures, current or past drug or toxin exposure, other medical problems and family history.

Next, doctors will typically perform a physical examination noting where the myoclonus occurs, if it's rhythmic or irregular, continuous or sporadic, if it occurs at rest or with voluntary movement, and whether it responds to stimuli such as touch, light, sound, or stretching a muscle.

To rule out potential causes, doctors may run tests to check for:

• Electrolyte, glucose, kidney, liver or thyroid malfunction
• Presence of paraneoplastic antibodies
• Presence of drugs or other toxins
• Irregularities in the brain or spine

To determine where in the nervous system the myoclonus originates, doctors will perform a series of neurophysiological tests, including specialized EEG (electrocephalography), EMG (electromyography) and/or combined EEG-EMG with evoked potential testing.

Types of myoclonus according to location include:

• Cortical — In the cortex or surface of the brain
• Cortical-subcortical — Co-activation between the cortex and subscortex (deeper in the brain)
• Subcortical-supraspinal — A focal or spreading activation from the subcortex to the top of the spine
• Spinal — In the spinal cord
• Peripheral — In the nerves outside of the brain or spine

When separated by cause they include:

• Physiological: patient is in normal health — sleep jerks are an example of this type
• Essential: without another underlying cause — sometimes hereditary
• Epileptic: part of a chronic seizure disorder
• Symptomatic or secondary: caused by another disorder

If the cause of the patient's myoclonus is still not clear, doctors may run additional tests including:

• MRI (magnetic resonance imaging)
• Cerebral spinal fluid exam
• Tests for malabsorption disorders
• Tests for enzyme deficiencies
• Biopsy of skin or leucocytes
• Copper studies
• Alpha-feto protein, cytogenetic analysis, radiosensitivity of DNA synthesis
• Genetic testing for inherited disorders, EPMI gene, mitochondria genes or huntingtin gene
• Mitochondria function studies