SAT-373 Veil of Hives: An Unusual Case Presentation of Autoimmune Thyroiditis as Acute Spontaneous Urticaria

Abstract Disclosure: N. Krueger: None. M. Shah: None. H. Alfar: None. R. Gajjar: None. D. Cornejo Gonzalez: None. D. Bisonó: None. G. Wilson: None. Introduction: Urticaria is a type of skin rash that leads to erythematous pruritic wheals that vary in size and distribution, with or without edema. Since the beginning of the 20th century, there has been an association of urticaria with autoimmune thyroid disease. We report a case where the only presenting symptom of autoimmune thyroiditis was a diffuse urticarial rash with angioedema. Case Report A 32 year old healthy female presented with new onset pruritic rash for 2 weeks. The rash worsened 3 days prior to presentation despite using OTC antihistamines along with development of orofacial swelling which prompted urgent medical evaluation. She reported sore throat, chills, and diffuse arthralgias involving her hands, knee and ankle joints but denied any other symptoms. She denied a history of similar symptoms, reported to have no allergies, recent sick contacts, pet exposure, or changes in hygienic routines within the past month. She immigrated from Venezuela 8 months before presentation and reported no significant travel history since arrival. She received a progestin dermal implant for contraception about 2 months prior and denied routine use of medications. On presentation, the patient was hemodynamically stable and afebrile. Initial otolaryngological evaluation showed no airway involvement. The patient was admitted to the medicine floor for further evaluation with the infectious disease and allergy-immunology teams consulted. Initial infectious workup was unremarkable including a rapid strep throat swab and full respiratory viral panel. She was given intravenous methylprednisolone, and H1 and H2 antagonists Famotidine and Diphenhydramine with slight improvement of her symptoms. Extended workup was pursued, with normal CBC, CMP, toxicology screen and urinalysis. Further infectious workup was unremarkable including Lyme serology, heterophile antigen test, anti-streptolysin O titers, and Epstein Barr virus, Coxsackie virus, Parvovirus B19, Hepatitis, and HIV. Autoimmune workup with ANA, RF, CCP and complement levels was unrevealing. C1q complement and C1INH were unremarkable. Thyroid function tests were sent due to generalized swelling, which came back significantly abnormal with TSH elevated to 145 (n 0.34-5.6 uIU/mL) and an undetectable free T4 (n 0.61-1.64 ng/dL). Anti-TPO antibodies were sent and elevated to >1000 (n <8.99 IU/mL). The Endocrinology team was consulted and after excluding concomitant adrenal insufficiency, the patient was started on levothyroxine. Her urticarial rash fully dissipated and she was discharged on levothyroxine and antihistamines. At 2 months follow up, she reported feeling well with no recurrence of symptoms. Conclusion: In patients that present with new onset urticarial rash of unclear etiology, it is imperative to check thyroid function tests as this is a potential dermatological manifestation of autoimmune thyroid disease. Presentation: Saturday, July 12, 2025