Asymmetric POSTS associated with unilateral EEG abnormalities

Summary

Objective

Positive occipital sharp transient of the sleep (POSTS) are considered a normal variant of non-REM sleep EEG. We describe a small series of patients with asymmetric POSTS and ipsilateral abnormal EEG findings.

Methods

Over a period of 30 weeks, we prospectively observed five consecutive subjects with strictly unilateral POSTS associated with ispilateral electrographic abnormalities. They represent 0.4% of all EEG performed over the same time lapse (5/1130), including inpatients, outpatients and long-term monitoring.

Results

Four women and one boy suffering from epileptic seizures (aged 7–76 years old) had unilateral POSTS, occurring only on the right side, during light sleep. They also presented ipsilateral epileptiform abnormalities.

Conclusion

The fact that POSTS were asymmetric and found only on the same side as the abnormalities raises the question whether these transients should still be considered physiological or could be interpreted at times as markers of underlying electrical abnormalities, pointing to an increased cortical excitability on the more active side. Although larger samples are needed to confirm our preliminary results, this case study questions the interpretation of POSTS as a uniformly normal variant.

Résumé

But

Les positive occipital sharp transient of the sleep (POSTS) sont considérés comme une variante de la norme de l’électroencéphalogramme du sommeil non REM. Une petite série de patients présentant des POSTS asymétriques associés à des anomalies EEG ispilatérales est décrite.

Patients et méthode

Sur une période de 30 semaines, cinq patients consécutifs ont présenté des POSTS strictement unilatéraux associés à des anomalies électrographiques ipsilatérales, représentant 0,4 % des enregistrements EEG effectués dans ce même temps (5/1130), y compris les patients hospitalisés, ambulatoires et les enregistrements de longue durée.

Résultats

Quatre femmes et un garçon ayant présenté une crise comitiale (âgés de sept à 76 ans) ont présenté des POSTS unilatéraux sur l’hémisphère droit lors du sommeil léger. Des anomalies épileptiformes ipsilatérales ont été observées.

Conclusion

Le fait que les POSTS soient asymétriques et seulement présents du côté où les anomalies épileptiformes ont été notées pose la question de savoir si les POSTS doivent toujours être considérés comme physiologiques ou devraient être interprétés parfois comme marqueurs d’une anomalie électrique sous-jacente, suggérant une excitabilité corticale accrue du côté plus actif. Bien qu’un échantillon plus large soit nécessaire pour confirmer nos résultats préliminaires, cette observation remet en question l’interprétation des POSTS comme une variante de la norme.

Introduction

Positive occipital sharp transients of sleep (POSTS) were first identified on EEG in 1950 [4] and have been accepted as being part of physiological sleep [3], [11]. POSTS appear as positive waves in the occipital region, occurring during all non-REM sleep stages; they are reported more often in subjects showing occipital lambda waves during the waking state, raising the possibility that POSTS might be related to the fixation of visual information [8]. They may have a shifting predominance [11]. POSTS are found on routine EEG including sleep in 50% [4] to 80% [2] of adult subjects, more often in young and middle-age adults, with a decline of prevalence after age 70 [12]; they are infrequently seen in infancy and early childhood and usually appear between 6–12 years, becoming more prominent in teenagers. A female preponderance has been reported [9]. There are rare descriptions of pathological conditions associated with POSTS, such as fainting spells [11], dysthymic disorder [7], headaches [10], and behavioural disorders with increased impulsivity [5]. In all these cases, there was no mention of asymmetrical POSTS.

To the best of our knowledge, the description of unilateral POSTS as a potential marker of abnormal EEG has not been reported yet. We describe here a small series of patients that we recently observed with asymmetric POSTS and ipsilateral abnormal EEG findings.