SMS: Physiology

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Stiffman Syndrome & Stimulus sensitive jerking: Neurophysiology

Stiffman syndrome

Continuous action potentials indistinguishable from voluntary activity
Persistent bursts: 50 to 60 ms duration; 5 - 6 Hz; Rhythmic; Synchronous
Interruption of bursts by spasms: Rapid activity; Full interference pattern; > 4 sec
Activity reduced by intravenous diazepam

Stimulus sensitive jerking: Neurophysiology ¹
	Pattern & Distribution	Burst duration	Habituation	Muscle recruitment order	EEG & Evoked potentials
Stiffman (Spasmodic reflex myoclonus)	Proximal > Distal Extensor General	> 500 ms	Prominent	↑ & ↓ from Spinal cord entry	Normal
Propriospinal Myoclonus	Axial Flexor General	40 to 140 ms	No	↑ & ↓ from Spinal cord entry	Normal
Hyperekplexia	Proximal > Distal Flexor General	20 to 400 ms	No	↑ & ↓ from 11^th nerve	± Epileptic EEG Large SEP
Reticular Reflex Myoclonus	Proximal > Distal Flexor General	20 to 50 ms	No	↑ & ↓ from 11^th nerve	Epileptic EEG Large SEP
Cortical Reflex Myoclonus	Distal > Proximal Multifocal	20 to 50 ms	No	↓ from 5^th or 7^th nerve	Epileptic EEG Large SEP
Psychogenic jerks	Inconsistent General	Variable	Yes	Variable	Normal

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References
1. J Neurol 1995;242:134-142

1/5/2017