Lance-Adams syndrome or chronic post-hypoxic myoclonus in adults: a systematic literature review.

Lance-Adams syndrome, or chronic post-hypoxic myoclonus, is a disabling chronic myoclonic disorder occurring in survivors of brain hypoxic events. Using a systematic methodology for literature search and data acquisition, we extensively reviewed all published cases of Lance-Adams syndrome since the first original patients were described by JW Lance and RD Adams in 1963. We analysed the available data of 272 patients extracted from the 153 included studies to summarize the natural history of Lance-Adams syndrome, outline the full spectrum of this disorder and deepen our understanding of its underlying mechanisms. Two-thirds of patients suffered from a respiratory hypoxic leading event. The main causes of anoxia were peri-surgery and anaesthetic accidents, asthma attacks/bronchospasm, cardiac disorders and intoxications/drug overdoses. Many patients exhibited a 'pure' Lance-Adams syndrome, characterized by multi-focal action-induced myoclonic jerks predominant to distal limbs. Morphologic brain imaging did not show any specific abnormalities. Neurophysiological evaluations, including EEG recordings, polymyography of myoclonus and jerk-locked back averaging of myoclonus, revealed features of cortical myoclonus in the majority of patients. Both EEG, showing epileptiform discharges on the frontal and central median regions, and brain metabolism imaging, showing hypometabolism on the pericentral regions, indicated that myoclonus in Lance-Adams syndrome originates within the motor cortex. Some anti-seizure medications have shown some effectiveness and certain neuromodulation techniques have promising effects.