Cerebellar clinical syndromes: the triad and rating scales

The last four decades have led to a clarification of the clinical deficits exhibited by cerebellar patients and a set of reliable and valid clinical ataxia rating scales are now available for both the assessment and follow-up of cerebellar ataxias. Cerebellar syndrome is now divided into three principal categories: the cerebellar motor syndrome (CMS), the vestibulo-cerebellar syndrome (VCS), and the cerebellar cognitive affective syndrome/ Schmahmann syndrome (CCAS/SS). CMS corresponds to motor impairments, including dysmetria, kinetic tremor, asynergia, dysdiadochokinesia, and dyschronometria. VCS includes oculomotor disturbances, such as saccadic dysmetria, jerky pursuit, downbeat nystagmus, and gaze-evoked nystagmus. CCAS/SS includes a spectrum of cognitive and affective deficits targeting executive functions, spatial cognition, language processing, and emotional regulation. The International Cooperative Ataxia Rating Scale (ICARS) was developed as an objective quantitative measure of cerebellar ataxias and assesses CMS and VCS, while the more streamlined Scale for the Assessment and Rating of Ataxia (SARA) was introduced specifically for the evaluation of motor deficits corresponding to the CMS. The Brief Ataxia Rating Scale (BARS) has also been proposed as a concise yet effective alternative, demonstrating enhanced efficiency and significant correlations with established cerebellar syndrome subtypes CMS/VCS. Furthermore, the Scale for Oculomotor Disorders in Ataxia (SODA) assesses the VCS, and the CCAS/Schmahmann Scale (CCAS-SS) and the Cerebellar Neuropsychiatric Rating Scale (CNRS and CNRS-2) assess the cognitive and emotional impairments in the CCAS/SS. Together with the Patient-Reported Outcome Measure of Ataxia (PROM-Ataxia) that covers all of these domains, the recognition of the three types of cerebellar syndrome and the application of validated clinician-administered and patient-completed rating scales represent a key step forward in the practice of ataxiology and training of students.