Origin

The syndrome may be the continuation of pre-existing acute post-anoxic myoclonus, or develop at some period after an acute insult, possibly representing an example of denervation supersensitivity.

Classification

None

Clinical Features

Commonly, the myoclonus appears days or weeks after the hypoxic episode when consciousness is regained. It is characteristic that the myoclonus is exacerbated during muscle activation (“action myoclonus”) or even intention (“intention myoclonus”). This is the most common clinical feature described and it significantly interferes with daily tasks and impairs the quality of life.

Action myoclonus may be a classical feature of the Lance-Adams (LA) syndrome, but it should be noted that action or intention myoclonus are typical features of the vast majority of conditions associated with myoclonus; the amplitude may be greater in LA syndrome, but the phenomenon is not a unique feature of the syndrome. It is also worth noting that distinguishing myoclonus on action from ataxia ( as defined as the breakdown or decomposition of a ballistic movement) is exceptionally difficult.

Similarly, various manifestations that typify reflex myoclonus such as a response to tactile or auditory stimuli are characteristic, but not pathognomonic, of LA syndrome.

Age of onset

From infancy to old age.

Distribution:

Tends to involve the whole body

Diagnosis:

Clinical, based on examination findings, in the appropriate historical context of patient who had definite or suspected cerebral ischaemia.

Differential Diagnosis

Diagnostic Tests

EEG may show spike and wave discharges in some cases.  The typical features which physiologically define cortical myoclonus may be present, but not invariably so.  Thus, some cases have enlarged SEPS, a “spike” arising from sensorimotor cortex elicited by jerk-locked averaging, and enhanced long-latency reflexes. The EMG discharge is brief during multifocal myoclonus, lasting 50–100 ms or less, with nearly synchronous EMG discharges in agonist, antagonists, and contiguous muscle segments.

Treatment

Clonazepam has long been recognized to be a very useful agent, but the drug of choice is likely to be levetiracetam. Valproic acid is also used, and all three drugs may be used in combination.

The following drugs were not found to be helpful in treating myoclonus: amantadine, phenytoin, tetrabenazine, nitrazepam, phenobarbitone, primidone, nortriptyline, and vasopressin. The role of DBS is unclear.