ABSTRACT
Introduction: There have been few reported cases of post-vaccination thyroiditis and Grave's disease. Here, we present a unique case of post vaccination thyroiditis associated with thyrotoxic myopathy after COVID-19 vaccination. Case Description: A 39-year-old man with no significant past medical history presented to the ED complaining of diffuse muscle pain, joint pain and stiffness for 2 days. He was unable to stand without support. On examination, he had normal deep tendon reflexes but decreased power on the right arm and leg. Admission labs revealed TSH of 0.008 (0.55- 4.7 uIU/mL), Free T4 2.49 (0.89 - 1.76 ng/dl) and FT3 7.4 (2.3-4.2 ng/dl), low potassium of 3.0 L (3.6 - 5.1 mmol/L) and normal CPK 135 (49 – 397 IU/L). MRI of the brain and cervical spine did not show any pathology. Muscle weakness was assessed to be from hypokalemia related to thyrotoxicosis. After potassium replacement, his symptoms improved but did not resolve completely. He was discharged home on methimazole and propranolol. During out-patient follow up 2 months later, his TFTs did not improve (FT4 2.90 ng/dl and TSH of 0.008 uIU/mL) with persistent muscle weakness and muscle aches despite normal potassium of 4.4 (3.6 - 5.1 mmol/L). TSI and TPO antibodies came back negative. Thyroid uptake and scan revealed decreased 4-hour (3.4%) and 24-hour (4%) uptake. Additional history revealed that he received his second dose of COVID-19 vaccine 6 days prior to onset of symptoms. At this point, a diagnosis of post COVID vaccination thyrotoxic myopathy was made. Methimazole was stopped and he was treated with a tapering dose of prednisone. His symptoms resolved completely with normalization of TFTs after a month (Free T4 1.28 ng/dl, TSH 2.993 uIU/mL). Discussion: Autoimmune thyroid disease including thyroiditis and Grave‘s disease have been reported after receiving COVID-19 vaccine. One of the mechanisms for this complication is thought to be autoimmune/inflammatory syndrome induced by vaccine adjuvants. This case illustrates the importance of keeping broad differentials in mind in patients who recently received COVID-19 vaccine especially as the pandemic persists and more people are being vaccinated.