MRI‐based volumetric differentiation of sporadic cerebellar ataxia

The term idiopathic cerebellar ataxia (IDCA) designates a variety of cerebellar syndromes that may present with a purely cerebellar syndrome (IDCA‐C) or with additional extracerebellar features (IDCA‐P). Multiple system atrophy is also a sporadic neurodegenerative disorder of unknown origin that may cause prominent cerebellar symptoms (MSA‐C). The final neuropathological answer to the question whether IDCA‐P and MSA‐C represent different varieties of one disease or two distinct entities is still lacking. Three‐dimensional MRI‐based volumetry allows morphological investigations intra vitam . Volumetric analysis of cerebellum, brainstem and basal ganglia was therefore performed in 46 patients with sporadic cerebellar ataxia and 16 age‐matched healthy controls. Patients with dementia were excluded from the study since cognitive impairment is an exclusion criterion for the diagnosis of MSA. Cerebellar patients were clinically divided into two groups: 33 patients with multiple system atrophy with prominent cerebellar symptoms (MSA‐C) and 13 patients with extracerebellar features not corresponding to MSA‐C (IDCA‐P). There was evidence for substantial cerebellar atrophy in both cerebellar groups while additional brainstem atrophy was significantly more pronounced in MSA‐C patients. Absolute caudate and putamen atrophy was found to be restricted to single MSA‐C individuals while group comparisons of mean volumes did not yield significant differences from controls. Based on the volumetric data, diagnosis could be correctly predicted in 94% of control, 82% of MSA‐C and 100% of IDCA‐P individuals. The finding of specific imaging characteristics strengthens (i) the value of MRI volumetry in separating MSA‐C from other types of sporadic cerebellar ataxia, and (ii) the hypothesis of two independent neurodegenerative disorders in MSA‐C and IDCA‐P. Received January 22, 2003. Revised May 15, 2003. Second revision August 11, 2003. Accepted August 16, 2003