P 80 Blink reflex recovery cycle in patients with genetically determined ataxias

Abstract

Objective To investigate the R2 blink reflex recovery cycle (BRRC) in genetically determined ataxias such as spinocerebellar ataxia (SCA), ataxia telangiectasia (AT) and Friedreich’s ataxia (FRDA). Background BRRC is known to be facilitated (enhanced) in movement disorders with basal ganglia involvement including Parkinson’s disease and isolated focal dystonias. The underlying mechanism though is not yet fully understood. Methods In an ongoing study, 22 patients (7 SCA1, 1 SCA2, 5 SCA3, 4 SCA6, 1 SCA17, 1 AT, 3 FRDA) with and without dystonia and 28 age and sex-matched healthy controls (HC) were examined. The BRRC was investigated using an air-puff stimulation at interstimulus intervals (ISI) of 200, 300, 500, 1000, and 3000 ms. EMG was recorded from the right orbicularis oculi muscle. To compare individual subjects, the area under the curve ratio values of R2 conditioned/R2 unconditioned were calculated. Clinical examination included a standardized video protocol and rating scales (e.g. scale for the assessment and rating of ataxia (SARA) and Fahn-Marsden-Score for Dystonia). For statistical analysis patients were grouped into those with ( n = 9) and without dystonia ( n = 13). Results The BRRC differed significantly ( p p = 0.078). A significant interaction of factors group and ISI ( p = 0.05) was found after taking dystonia as additional feature into account (see Fig. 1 ). Conclusions To our knowledge, this is the first study investigating the BRRC in genetically defined ataxia patients. So far, in patients with Parkinson’s disease and isolated dystonias the BRRC was facilitated suggesting deficient inhibition of basal ganglia - brainstem interaction mediating this response. In contrast, in ataxia patients reported here, there was a tendency towards stronger inhibition of the BRRC. This may reflect a pathologic cerebellar influence on these circuits. This is further corroborated by a significant interaction of the factors group and ISI when dystonic features were taken into account. Our ongoing investigations will clarify, if the reported effect withstands to significance and whether other clinical markers such as SCA subtype or symptom severity correlate with our electrophysiological findings.