UC Irvine

Definitions and Diagnosis of Myoclonus Myoclonus (from the Greek myo, “muscle”, and klonus “agitation/violent contraction”) has been defined as a “sudden, involuntary, brief, shock-like muscle contraction arising from the central nervous system” (CNS) [Fahn et al., 1986]. Myoclonus may be focal or generalized, single or repetitive, rhythmic or irregular. The origin of myoclonus may involve the spinal cord, cortex, brainstem, and cerebellum and provides the basis for several of many classifications of myoclonic movements [Serratosa and Delgado-Escueta, 1993]. The range of myoclonic phenomena includes nonepileptic events such as sleep myoclonus, opsoclonus-myoclonus, and narcotic-induced myoclonus (Fig. 46-1). Epileptic myoclonus types include progressive disorders and nonprogressive syndromes such as juvenile myoclonic epilepsy. This chapter presents the spectrum of myoclonic events observed in the neonate, infant and child, to distinguish myoclonic seizure syndromes from other entries, and provides current information on and practical guidelines for the diagnosis and management of discrete types of myoclonic seizures. In addition, the diagnosis and management of infantile spasms, traditionally grouped with the myoclonic epilepsies, are discussed.