Thyrotoxicosis misdiagnosed as anaphylaxis following NSAID use in an adolescent

Emergency physicians often encounter patients presenting with symptoms suggestive of common conditions, such as anaphylaxis. However, when clinical findings deviate from the expected course, maintaining a broad differential is critical. A 17-year-old female presented to the emergency department with flushing, and tachycardia following ibuprofen ingestion.The patient had administered intramuscular epinephrine at home prior to arrival. In the emergency department, she was treated with antihistamines for a presumed anaphylactic reaction. While what was perceived as her facial swelling and hives improved, she remained persistently tachycardic and hypertensive. Further evaluation revealed suppressed TSH and elevated free T4 levels, leading to a diagnosis of thyrotoxicosis. Endocrinology consultation confirmed the findings. The patient was treated with atenolol for symptomatic relief and methimazole to address the underlying thyroid dysfunction. Why Should an Emergency Physician Be Aware of This?: This case underscores the importance of re-evaluating initial impressions when a patient's response to treatment is incomplete or atypical. Persistent tachycardia and hypertension after apparent anaphylaxis should prompt consideration of alternative diagnoses, including thyrotoxicosis. Emergency physicians must remain vigilant for less common presentations of thyroid dysfunction, especially when triggered by medications or other stressors, to ensure timely diagnosis and management.