Defining Hand Stereotypies in Rett Syndrome: A Movement Disorders Perspective

INTRODUCTION

Hand stereotypies (HS) are a primary diagnostic criterion for Rett syndrome (RTT) but are difficult to characterize and quantify systematically.

METHODS

We collected video on 27 girls (2-12 years of age) with classic RTT who participated in a mecasermin trial. The present study focused exclusively on video analyses, by reviewing two five-minute windows per subject to identify the two most common HS. Three raters with expertise in movement disorders independently rated the five-minute windows using standardized terminology to determine the level of agreement. We iteratively refined the protocol in three stages to improve descriptive accuracy, categorizing HS as "central" or "peripheral," "simple" or "complex," scoring each hand separately. Inter-rater agreement was analyzed using Kappa statistics.

RESULTS

In the initial protocol evaluating HS by video, inter-rater agreement was 20.7%. In the final protocol, inter-rater agreement for the two most frequent HS was higher than the initial protocol at 50%.

CONCLUSION

Phenotypic variability makes standardized evaluation of HS in RTT a challenge; we achieved only 50% level of agreement and only for the most frequent HS. Therefore, objective measures are needed to evaluate HS.

Unilateral rhythmic hand tapping in Rett syndrome: is this stereotypy?

Rett syndrome is a severe neurodevelopmental disorder, with hand stereotypies as a hallmark of the disease. Epilepsy is a frequent comorbidity and is accompanied by centrotemporal spikes on electroencephalogram, but stereotypic movements should not have epileptiform correlates. During routine video-electroencephalographic investigation in 5 Rett syndrome patients, we identified a peculiar type of unilateral, highly rhythmic hand tapping accompanied by contralateral synchronous centrotemporal spikes on electroencephalography. This phenomenon is not consistent with either reflex seizures or hand stereotypies and does not respond to antiepileptic drugs. The electroencephalographic activity probably represents evoked potentials, either somatosensory or motor, whereas the rhythmic activity raises the possibility of a subcortical pacemaker for a stereotypy variant. The phenomenon could be caused by abnormal circuitry among the hyperexcitable somatosensory cortex, motor cortex, and subcortical areas in Rett syndrome. Clinicians should be aware of the nonepileptic nature of this motor behavior and should not attempt to treat it.