[A case of stimulus-sensitive segmental spinal myoclonus]

Area of Science:

• Neurology
• Neurophysiology

Background:

• Spinal myoclonus is a rare neurological disorder characterized by involuntary muscle contractions.
• Understanding the origin and characteristics of spinal myoclonus is crucial for effective diagnosis and treatment.

Observation:

• A 37-year-old male presented with one month of periodic, synchronous myoclonus in the right shoulder and diaphragm muscles.
• Neurological examination was normal except for the myoclonus, which was synchronous with diaphragmatic contractions and appeared to originate from the C4-C5 spinal segments.
• The myoclonus disappeared during sleep and was enhanced by voluntary muscle contraction but not by mental stress.

Findings:

• Diagnostic tests including MRI, EEG, and evoked potentials were normal, supporting a spinal origin.
• Treatment with clonazepam and phenytoin decreased the myoclonus frequency and rhythmicity, making it stimulus-sensitive (tapping, electric shock) with an 800 ms refractory period.
• The initial lack of stimulus sensitivity was attributed to the refractory period.

Implications:

• This case highlights spinal myoclonus as a distinct entity potentially originating from cervical spinal segments.
• Pharmacological agents like clonazepam and phenytoin can be effective in managing spinal myoclonus.
• Further research into the neurophysiological mechanisms of spinal myoclonus is warranted.