Diagnosis of Hashimoto encephalopathy can be made when all six of the following criteria have been met:

1. Encephalopathy with seizures, myoclonus, hallucinations, or stroke-like episodes
2. Subclinical or mild overt thyroid disease (usually hypothyroidism)
3. Normal brain MRI or with non-specific abnormalities
4. Presence of serum thyroid (thyroid peroxidase, thyroglobulin) antibodies
5. Absence of well-characterized neuronal antibodies in serum and CSF
6. Reasonable exclusion of alternative causes

A team of leading autoimmune encephalitis researchers have proposed that the term Hashimoto’s encephalopathy only be used when rigorous clinical assessment and comprehensive testing for well characterized neuronal antibodies exclude other potential causes of encephalopathy. The underlying cause of Hashimoto’s encephalopathy is unclear. Experts in the field recommend that cases of Hashimoto’s encephalopathy be classified as probable autoimmune encephalitis.