The “allergy epidemic” of the Western World, has led to an overwhelming number of emergency department presentations with allergic rhinitis, allergic conjunctivitis, atopic eczema, and asthma. Careful consideration should be given to screening for the typical signs and symptoms of Mixed connective tissue disease (MCTD) in patients presenting to the ED with what appears to be a simple allergic process. MCTD is a rare systemic rheumatic disease characterized by high levels of anti-U1RNP antibodies and various clinical signs and symptoms. The pathophysiology of MCTD is poorly understood. An association between allergen-mediated processes and MCTD has been reported in recent literature. Our case report involves a 40 year old African American female with initial outpatient presentation suggestive of atopic disease, with progressive worsening of symptoms while receiving allergen immunotherapy. The patient presented to the emergency department with bilateral leg cramping. The patient was found to have a CPK of 7000 unresponsive to fluids. The patient was evaluated by the Allergy and Rheumatology services. The patient was ultimately diagnosed with MCTD-Myositis Overlap Syndrome and started on steroids and IVIG with improvement in symptoms. While MCTD is not a diagnosis readily made in the ED, early identification and treatment of the disease is critical for prevention of long term complications.Copyright © 2023 Elsevier Inc. All rights reserved.