2018 年 35 巻 3 号 p. 320-325
“Cortical cerebellar atrophy (CCA)” is a neuropathologically–defined disease entity, which is characterized by pure cerebello–olivary degeneration. Corresponding to the neuropathological findings, CCA patients are believed to show purely cerebellar ataxic syndrome, however, some cases with pathologically–proven CCA have been reported to show extracerebellar features such as involuntary movements, cognitive decline or decreased vibration sense. On the other hands, some cases with a clinical diagnosis of CCA have revealed affected lesions outside the cerebello–olivary system by postmortem examinations. These facts suggest the so–called “CCA” may have a clinical and neuropathological heterogeneity.
The heterogeneity is partly due to the uncertainty of the diagnosis of CCA. There is no specific biomarker for cerebello–olivary degeneration, therefore, the diagnosis of CCA is largely dependent on the exclusion of other diseases with cerebellar ataxia at present. Firstly, we should exclude olivopontocerebellar atrophy (OPCA, alternatively, multiple system atrophy with predominant cerebellar ataxia: MSA–C) because it accounts for approximately 60–70% of sporadic ataxias in Japan. It is sometimes quite difficult to distinguish OPCA (MSA–C) in the early stage of disease (less than 5 years from onset) from CCA. Secondly, hereditary ataxias need to be excluded. It is known that 10–20% of apparently sporadic cases are proven to have one of common autosomal dominant cerebellar ataxias (especially, SCA6, SCA31 in Japan) when genetic testing is conducted. Further, next generation sequencing has increasingly identified rare disease–causing variants in apparently sporadic cases. Lastly, secondary ataxias should be addressed by means of a detailed medical history and physical examination, as well as a focused diagnostic evaluation. Acquired causes for cerebellar ataxia include autoimmune–mediated, toxic (alcohol, drugs), demylinating, vascular, metabolic, infectious (parainfectious), others (PSP–C, prion disease, superficial siderosis, etc.). Approach to the acquired causes is very important because some of them are medically actionable.
Here we have replaced the neuropathologically–based nomenclature “CCA” with the clinical–based one “idiopathic cerebellar ataxia (IDCA)” to refine sporadic, degenerative cerebellar ataxia of adult–onset and proposed its diagnostic criteria.
