MELAS is an acronym for the convergence of mitochondrial myopathy, encephalopathy, lactic acidosis and stroke like episodes. It was described by Pavlakis et al. in 1984.

Introduccióna encefalopatía hipóxico-isquémica retardada (EIHR) se presenta como una enfermedad desmielinizante del sistema nervioso central (SNC)

Lance-Adams syndrome was described in 1963 is a rare complication due to recovered hypoxic episodes or prolonged hypotension events. Is characterized by action myoclonus and cerebellar ataxia. We report two patients studied with this syndrome. A 51 year-old men and a 72 yearsold men fully recovered after a brief cardiorespiratory arrest they developed intention myoclonus, triggered by voluntary movements, posture, also by sounds, touches and emotional stimuli. It also was accompanied by cerebellar syndrome, ataxia and posture control alterations. They had a Magnetic Resonance (MR), EEG and normal metabolic parameters. Myoclonus was treated with sodium valproate and clonazepam. The neurophysiologic interpretation of this motor imbalance is an abnormal functioning of the Central Pattern Generator Netwoks (CPGN) located in the mesencephalic region. Hypoxic lesions in vermian purkinje and paravermal cerebellum neurons have an inhibitory effect in this system, producing motor control attenuation, generating an imbalance in the motoneurons of the spinal cord contraction sequence, which starts shooting in an uncoordinated way. As in almost all cerebellar lesions with time they tend to compensate and to diminish myoclonus.