Introduction

Paroxysmal dyskinesias (PDs) refer to relatively brief attacks of abnormal movements and postures with return to normal between episodes. The abnormal movements consist of dystonia, choreo-athetosis, and ballism, often in combination. The duration is variable, from very short attacks lasting a few seconds to prolonged ones, lasting several hours. The frequency is variable, as is the side of the body involved. PDs can be sporadic or familial with autosomal dominant inheritance or can be symptomatic of different conditions (Bressman et al., 1988; Fahn, 1994; Demirkiran & Jankovic, 1995).

Since the first description by Mount and Reback (1940), numerous reports of patients with PDs have followed and several classifications, based on duration of attacks and etiology have been proposed (Lance, 1977; Goodenough et al., 1978; Fahn, 1994). The most recent one classifies PDs according to the precipitating events and distinguishes the following forms: paroxysmal kinesigenic dyskinesias (PKD), paroxysmal non-kinesigenic dyskinesias (PNKD), paroxysmal exertioninduced dyskinesias (PED), paroxysmal hypnogenic dyskinesias (PHD) (Demirkiran & Jankovic, 1995).

The purpose of the chapter is to describe the clinical features of the classical forms of PDs including benign paroxysmal torticollis of infants (BPT) and paroxysmal tonic up-gaze deviation of infants (PTUDI) and to review the more recent data on pathophysiology of PDs as derived from genetic studies and from animal model.

Clinical features

Paroxysmal kinesigenic dyskinesia (PKD)

Most cases of PKD are idiopathic, both familial with autosomal dominant pattern of inheritance or sporadic, but cases of symptomaticPKDare reported (Fahn, 1994; Marsden, 1996; Demirkiran & Jankovic, 1995; Hwang et al., 1998).