Lance and Adam described a myoclonus with onset after a hypoxic event causing hypoxic encephalopathy.
The patient develops rapid, diffuse and uncontrollable muscle jerks.
The onset is after a hypoxic event such as a near-fatal cardiac arrest. Some cases occur after an acute asthmatic attack.
There are two main forms:
(1) acute, with onset within 24 hours of the hypoxic event. The patient is often deeply comatose.
(2) chronic, with onset days to weeks after the injury
Features of chronic posthypoxic myoclonus:
(1) There is a multifocal cortical action myoclonus.
(2) This may be combined with stimulus-sensitive, bilateral and generalized jerks.
(3) It may be accompanied by dysmetria, dysarthria and/or ataxia.
(4) Cognitive functions are preserved or mildly affected.
(5) The patient may be disabled if the myoclonus is severe and frequent while the patient is conscious.
(6) There tends to be improvement over time.
