Idiopathic Late-Onset Cerebellar Ataxia: This condition is characterized by progressive cerebellar ataxia without a clear cause, often presenting in older adults. The lack of positive findings on imaging studies supports this diagnosis, as it is primarily a clinical diagnosis.

Alcohol-Related Cerebellar Degeneration: Chronic alcohol abuse can lead to cerebellar ataxia. Even if the patient does not have a history of alcoholism, subtle or denied alcohol use could contribute to ataxia.
Vitamin Deficiencies (e.g., Vitamin B12, Vitamin E): Deficiencies in certain vitamins can cause progressive ataxia. These are important to consider because they are potentially treatable.
Spinocerebellar Ataxias (SCAs): While SCAs typically present earlier in life, some forms can have a later onset. A family history might support this diagnosis, but some cases can be sporadic.

Paraneoplastic Cerebellar Degeneration: This is a rare but potentially treatable condition associated with various cancers. It's crucial to consider and investigate for underlying malignancy, especially given the patient's age and the potential for cancer.
Creutzfeldt-Jakob Disease: Although rare, this prion disease can present with ataxia and rapidly progressive dementia. Its fatal outcome and transmissibility make it a "do not miss" diagnosis.
Toxic Exposures: Certain toxins (e.g., heavy metals) can cause ataxia. Identifying and removing the source of exposure can halt progression.

Mitochondrial Disorders: These can present with cerebellar ataxia among other systemic symptoms. They are genetic and can have a variable onset, including late in life.
Ataxia-Telangiectasia: Typically presents in childhood, but very rare cases might have a later onset. It's characterized by ataxia, telangiectasias, and immunodeficiency.
Gluten Ataxia: A form of ataxia associated with gluten sensitivity or celiac disease. It's an important consideration because it's potentially treatable with a gluten-free diet.