As you mentioned, there are acquired, non-genetic causes (such as vitamin deficiencies and tumors) as well and other diseases (such as some mitochondrial diseases and
multiple sclerosis) which can cause ataxia. Genetic testing results as well as other tests results, such as your MRI, will help your neurologist in making an accurate diagnosis.
As you know, there is currently no cure or effective treatment for spinocerebellar ataxia.