Excerpta #: EE-01 F Mossa-Basha 1, M Stone 1, N Shabeeb 2, D Pinkney 1, H Marin 1 1 Henry Ford Health System, Detroit, MI 2 Indiana University Health, Indianapolis, IN

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Steroid-responsive encephalopathy associated with autoimmune thyroiditis (SREAT) aka Hashimoto's encephalitis is a well recognized but poorly understood complication of autoimmune thyroid disease. This electronic excerpta demonstrates a case of Hashimoto's encephalitis with migratory encephalitis and findings suggestive of a vasculitic association.

Clinical Presentation A 41-year-old female presenting with a ten day history of word finding difficulty, which spontaneously resolved a week later. Subsequently, she developed left upper extremity parasthesias. 3 months later, the patient suffered a generalized tonic clonic seizure. Labs values :  Anti-thyroid peroxidase antibody: >1300 U/ml (reference range < 60 U/mL)  Anti-thyroglobulin antibody: 373 U/mL (reference range < 60 U/mL)  ANA: weakly positive  CSF analysis + culture: negative  B. Burgdorferi immunoassay: negative

Fig 1: Day 0: T2 FLAIR demonstrates hyperintense cortical and subcortical signal in the left temporal lobe (A). 3 months later: The previous abnormality has resolved (B), with a new T1 cortical and subcortical hypointense signal in the right frontotemporoparietal region (C). 9 months after initial presentation: The previous abnormality has resolved with new T1 hypointensity in the right tempero-occipital lobe (D). Figure 1 AB CD T2 FLAIR SAG T1 Day 0 3 months 9 months Migratory Encephalitis

Fig 2: T2WI demonstrate cortical and subcoritcal hyperintensity in the right frontotemporoparietal region (A). Post contrast images demonstrate no enhancement (B). No restricted diffusion is present on DWI (C) and ADC (D). AB CD Figure 2 T2WI DWI POST T1 ADC 3 months after initial presentation

AB Figure 3 3 months after initial presentation

Pathogenesis remains poorly understood Proposed etiologies:  Autoimmune demyelination  Vasculitis, with or without immune complex deposition  Anti-CNS antibodies

Sparse reports in the literature regarding pathologic findings of SREAT include:  Lymphocytic perivenular cuffs  Vasculitis of venules and arterioles  Microglial activation  Primary demyelination

Generally accepted diagnostic criteria include:  Elevated anti-thyroid antibodies  Steroid responsive encephalopathy  Cognitive impairment, focal neurologic deficit, movement disorders, and/or seizures. Laboratory analysis: CSF titers of anti-thyroid antibodies are the most specific test. Serum anti-thyroid antibodies are elevated in 10% of healthy adults.

50% of patients with SREAT have normal neuroimaging. The remaining 50% have diffuse or focal areas of T1 hypointensity/T2 hyperintensity in the cerebral white matter. Parenchymal and/or dural enhacement is uncommon. DWI abnormalities related to ischemia can be seen, supporting the theory of a vasculitic process.

Reports of angiographic findings are sparse with 5 cases reported in the literature:  4 cases showed no abnormality.  1 demonstrated decreased lesional transit time, similar to our patient.  Classical angiographic findings of vessel narrowing related to vasculitis are not reported. The arterial hyperperfusion and arteriovenous shunting seen in our patient are suggestive of a microvascular abnormality. Together with prior reported biopsy results and steroid responsivity support the theory that SREAT reflects a microvascular vasculitis.

SREAT aka Hashimoto's encephalitis remains poorly understood with limited specific criteria. MR findings are often absent or nonspecific. Migratory cortical and subcortical T2 prolongation can be seen. A vasculitic pathophysiology is suggested in Pathology reports and imaging literature. AB

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