Sporadic Spinocerebellar Ataxia

About 1/3 of SCA patients do not appear to suffer from a form of familial SCA. Patients with sporadic ataxia usually have one of two clinical presentations. Approximately 1/3 of these patients develop a condition characterized by cerebellar ataxia alone, i.e., with little or involvement of other regions of the nervous system. These patients have a more slowly progressive form, may remain ambulatory for well beyond 5 years, and do not have a shortened life span. The remaining approximately 2/3 of sporadic ataxia patients develop a form of multiple system atrophy (MSA), characterized by ataxia associated with a combination of dementia, ophthalmoplegia, bulbar findings, tremor, bradykinesia or rigidity, autonomic dysfunction or other neurological abnormalities. These patients often have a more aggressive course leading to confinement to wheelchair by 5 years and in which frequent aspiration, reduced respiratory drive, or urinary retention lead to premature death by respiratory failure or sepsis. Conditions that may present as a form of sporadic SCA include Creutzfeldt-Jakob disease, subacute cerebellar degeneration, hypothyroidism, vitamin deficiency, chronic ethanol abuse, or a mitochondrial disorder. Sporadic ataxia has been associated with several different autoantibodies, although this finding is more typical of subacute cerebellar degeneration. Nevertheless, the majority of patients with sporadic ataxia have a truly idiopathic condition. After excluding a role for medical causes, such as diabetic polyneuropathy, hypothyroidism or vitamin deficiency, of ataxia in a given patient, consideration should be given to rare, but potentially identifiable conditions. Included among these are ataxia associated with antibodies, and ataxic variants of prion disease.