SAT-465 Steroid-Responsive Encephalopathy Associated with Autoimmune Thyroiditis: Diagnosis or Distraction?

In 1966 a case of episodic encephalopathy with anti-thyroid antibody (ATAb) positive Hashimoto’s thyroiditis was first reported. Controversy persists regarding Hashimoto’s encephalopathy, now known as steroid-responsive encephalopathy associated with autoimmune thyroiditis (SREAT) and any relationship with ATAb. There is no literature supporting an etiologic role of ATAb in SREAT. Nor has there been correlation shown between ATAb titer and severity of thyroid dysfunction or SREAT(1). A 56 yo female was admitted to a community hospital three times with visual hallucinations and slurred speech. Brain MRI, LP and standard tests including C3/C4, folate, B12, ANA and ANCA were unrevealing. Thyroglobulin antibodies (TgAb) and anti-thyroid peroxidase antibodies (TPOAb) were positive. Diagnosed with SREAT with relief of symptoms on high dose IV corticosteroids. Discharged on oral prednisone. Seven months later she began experiencing progressive proximal weakness of all extremities associated with exertional dyspnea, fatigue and weight gain. EMG studies indicated steroid-induced myopathy of the proximal extremities. After prednisone tapering, she was admitted to our institution with acute confusion, blurred vision, fever, tachycardia, tachypnea and hypoxemia. Examination showed Cushingoid features. Labs showed hyperglycemia, ANA (+), TPOAb (+), TgAb (+), low FreeT4, low T3, normal TSH and elevated IgG in the CSF. Brain MRI showed meningeal enhancement of parieto-occipital lobes and left tentorium. Empiric antibiotics started to cover infectious meningoencephalitis. Endocrinology consulted for iatrogenic Cushing’s syndrome with hyperglycemia, abnormal thyroid function tests (TFTs) with positive ATAb and evaluation for SREAT. We recommended tapering steroids and evaluation for infectious, autoimmune or paraneoplastic causes of encephalopathy, before presuming SREAT. Rheumatological and infectious work-up was negative. CT chest showed nodular densities and CT abdomen showed hepatic, splenic and right inguinal region masses. Biopsy of inguinal mass showed Diffuse Large B-cell Lymphoma confirmed on bone marrow biopsy. CSF flow cytometry was unrevealing, likely due to prior steroids. Leptomeningeal enhancement likely reflected leptomeningeal metastases. Treated with systemic R-CHOP, high dose MTX, intrathecal MTX, cytarabine and corticosteroid tapering. Complete remission was achieved with normalization of TFTs, resolution of her Cushingoid and encephalopathic features. This case illustrates SREAT as a diagnosis of exclusion. ATAbs may be positive in non-thyroid autoimmune disorders, other neurological conditions and 10-20% of the general population (2). B cell lymphoma with leptomeningeal metastasis caused encephalopathic features which improved with corticosteroids. Ascribing a diagnosis of SREAT led to delayed cancer diagnosis and treatment.