Myoclonic Status in Nonprogressive Encephalopathy

Bernardo Dalla Bernardina

Introduction

Despite the existence in the literature of proof of the possible occurrence in infants and young children of an absence status with myoclonias of variable severity and duration called by various names, such as “minor epileptic status,” “minor motor status,” “myoclonic status,” “obtundation with myoclonias,” “nonconvulsive states with ataxia,” “myoclonic state with impaired consciousness,” “myoclonic status in symptomatic cases of myoclonic astatic epilepsy,” and so on,¹^,²^,³^,⁶^,⁹^,¹⁰^,²⁴^,²⁷^,²⁸^,³²^,³⁶^,³⁸^,⁴² reports documenting the existence of an epileptic syndrome characterized by the recurrence of long-lasting or subcontinuous myoclonic status in children with a nonprogressive encephalopathy are relatively rare.⁷^,¹¹^,¹³^,¹⁵^,¹⁶^,¹⁸^,¹⁹^,²⁰^,²¹^,²⁵^,³³ In fact a very similar electroclinical picture has been described in children with Angelman syndrome,⁸^,²⁵^,³³^,³⁴^,³⁵^,³⁷^,³⁹^,⁴¹^,⁴³^,⁴⁵^,⁴⁷^,⁵² in some children with 4p- syndrome,⁴⁴^,⁴⁶^,⁵³ and in some children with Rett syndrome,¹⁷ but very few authors have stressed how, in these cases, the electroclinical picture was typically that of “myoclonic status in nonprogressive encephalopathy,”¹⁵^,¹⁶^,¹⁷^,¹⁸^,¹⁹^,²²^,⁴⁰^,⁴⁴ a syndromic entity recently proposed by the ILAE Task Force on Classification and Terminology⁴¹ in its category “syndromes in development.”

Definitions

The syndrome is characterized by the recurrence of long-lasting myoclonic status, that is often difficult to recognize and frequently refractory to different treatments, in children with a nonprogressive encephalopathy of variable etiology.

Epidemiology

The prevalence of this condition is unknown; it seems to be rare because the only three series available⁷^,¹¹^,¹⁷ account for a total of 96 cases. The true prevalence is probably higher than reported, considering that many similar cases can remain misdiagnosed particularly in the absence of polygraphic recordings. There appears to be a female predominance, with a male:female ratio of 1:2. Familial antecedents for epilepsy are present in about 15% of cases.

Etiology and Basic Mechanisms

A genetic disorder (4p- syndrome, Rett syndrome, and especially Angelman syndrome) is present in nearly half of the reported cases. In such cases, nonsignificant abnormalities are neuroradiologically detectable.

Only gold members can continue reading. Log In or Register to continue