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Hashimoto's Encephalitis (Steroid Responsive Encephalopathy Associated with Autoimmune Thyroiditis [SREAT])

Primer

Hashimoto's Encephalopathy (HE) (also known as Steroid Responsive Encephalopathy Associated with Autoimmune Thyroiditis [SREAT]), is a rare, clinically heterogeneous neurological disorder associated with Hashimoto's disease and positive thyroid autoantibodies. It is is a form of autoimmune encephalitis. It is increasingly recognized as an important and treatable cause of autoimmune encephalitis, though remains somewhat controversial as a diagnosis.

Epidemiology
Comorbidity

Diagnostic Criteria

Diagnosis can be made when all 6 of the following criteria have been met (Graus et al. 2016):[1]

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

Symptoms

The clinical presentation of HE can include seizures, myoclonus, hallucinations, and stroke-like episodes with normal or non-specific CSF and brain MRI abnormalities.

Controversial Diagnosis

Hashimoto’s encephalopathy should be diagnosed only when a thorough clinical assessment has been performed, including comprehensive testing for well characterized neuronal antibodies, and ruling out other potential causes of encephalopathy or encephalitis. In essence, it should be a diagnosis of exclusion.

Pathophysiology

Differential Diagnosis

Investigations

  • anti-TPO (thyroid peroxidase antibody), anti-thyroglobulin, and anti-dsDNA can be elevated in HE
    • Thyroid peroxidase antibody is elevated in over 90% of cases of Hashimoto’s thyroiditis.
    • Although the test has a false positive rate of up to 20%, a positive result may indicate SREAT, and should prompt a thorough search for neurological symptoms that might support a diagnosis of encephalopathy.

Thyroid Antibodies Are Non-Specific!

Thyroid antibodies are not specific for Hashimoto’s encephalopathy. They can be present in up to 13% of healthy individuals, and up to 27% in white women older than 60 years. It can also be present in other autoimmune encephalitis disorders.

Treatment

Patients with a non-specific encephalopathy with subclinical or overt thyroid disease, anti-thyroid antibodies, and no other explanation for the symptoms should be considered for a trial of steroids. Most patients treated with corticosteroids with or without levothyroxine will have clinical improvement.[2]

Resources

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Articles
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References

1) Graus, F., Titulaer, M. J., Balu, R., Benseler, S., Bien, C. G., Cellucci, T., ... & Glaser, C. A. (2016). A clinical approach to diagnosis of autoimmune encephalitis. The Lancet Neurology, 15(4), 391-404.
2) Chong, J. Y., Rowland, L. P., & Utiger, R. D. (2003). Hashimoto encephalopathy: syndrome or myth? Archives of neurology, 2, 164–171.