SAT-066 Auto-Destruction of the Thyroid and Coexisting Glutamic Acid Decarboxylase Mediated Neurological Disease in an Adolescent: An Unusual Presentation of Autoimmunity
Authors: Murthy Deepa Badrinath , Alvarez Ana Gutierrez , Vargas Wendy S , Litao Melissa Kaori Silva , Shah Bina Cherryl 
Published: May 2020

Abstract
BACKGROUND: Autoimmune thyroiditis (AT) is a common cause of acquired hypothyroidism in children characterized by lymphocytic thyroid infiltration. Sometimes gradual thyroid failure occurs due to apoptosis of thyroid cells. It may occur via apoptotic cytokines, ligands and receptors, including T regulatory cells, tumor necrosis factors etc. AT can coexist with other organ specific autoimmune conditions. Rarely neurological autoimmunity due to glutamic acid decarboxylase (GAD) antigen may be associated with AT. In fact, up to 70% of patients with GAD 65 neuropathy may have other autoimmune disease (AT, type 1 diabetes, pernicious anemia). We present a case of AT that led to total destruction of the thyroid gland with coexisting neurological autoimmunity.
CLINICAL CASE: A 7 yr old male presented with tiredness, heat intolerance and weight loss for 4 months, unsteady gait with frequent falls for 2 weeks. Exam showed tachycardia, firm thyromegaly and difficulty with tandem walking without other cerebellar signs. Labs showed undetectable TSH, elevated FT3, FT4 with positive thyroid antibodies, and negative for viral serology. MRI brain was normal and neurological symptoms resolved within few weeks. Thyroid ultrasound (TUS) showed hypervascularity and heterogenecity with right lobe volume (RLV) 2.8 cc, left lobe volume (LLV) 2.3cc with 0.9cm nodule. Thyroid scan showed increased uptake (52% and 61% at 4, 24 hrs). He required methimazole for 2.2 yrs. Five months later, at age 9.6 yrs he was hypothyroid and was started on Levothyroxine(LT4). TUS showed RLV 4.6cc, LLV 2.5cc and solid left nodule 1.2cm. FNA was consistent with AT. At age 14.4 yrs,TUS showed near complete involution of RL and isthmus with LLV 4.9cc and 0.6cm nodule and thyroid scan was negative for uptake. Repeat FNA reconfirmed AT. Due to progressive atrophic thyroiditis he had hyperthyrotropinemia with euthyroxinemia (TSH range 12–165, Normal FT4 1.15–1.73) requiring increasing dose of LT4 over nearly 7.6 yrs.
At 14.8 yrs, he developed focal epilepsy treated with Levetiracetam and new-onset left fourth cranial nerve palsy. Autoimmune workup revealed extremely elevated GAD 65 antibodies in serum and cerebral spinal fluid, 1703 and 14.2 nmol/L respectively (N&lt;0.02), confirming a diagnosis of GAD-65 central nervous system disease. He is currently receiving monthly IVIG.
At 15.3 yrs, complete atrophy of RL with involuting LLV 2.4cc was noted. He remains euthyroid and seizure free on anti-epileptics with recovering cranial nerve palsy.
CONCLUSION:
This is an unusual and extreme form of atrophic thyroiditis leading to near total destruction of thyroid gland related to apoptosis with autoimmunity. GAD-65 CNS autoimmunity is important to be considered in children with AT presenting with seizures or focal neurological signs. Continued vigilance and follow up for the development of other autoimmune conditions is warranted.