Unique Presentation of Thyrotoxic Periodic Paralysis With Urticarial Dermographia

Thyrotoxic periodic paralysis (TPP) is an acute complication of hyperthyroidism. Thyrotoxic periodic paralysis is treatable, and the management consists of potassium correction, beta-blockers, and antithyroid drug (ATD) therapy. While TPP is well described in the literature, we describe a case of TPP with urticarial dermographia (UD) that resolved with a short course of antihistamines while continuing ATD therapy. To the best of our knowledge, this is the first reported case of UD after methimazole (MMI) therapy in a TPP patient. A 25-year-old Cambodian active duty male with no significant past medical history presented to the emergency department with acute loss of lower extremity muscle tone with hypokalemia in the setting of previously undiagnosed Graves' disease (GD). He was started on MMI but within 2 weeks developed a rash consistent with UD. This was successfully treated with a second-generation antihistamine while continuing his MMI. Thyrotoxic periodic paralysis is primarily treated by controlling the underlying thyroid disease causing paralysis. Methimazole is commonly chosen as a treatment due to its rapid efficacy and long duration of action. However, adverse effects like UD can occur. Current recommendations are that minor cutaneous reactions can be treated with antihistamines for the management of Graves' disease. However, this case and others show that even moderate reactions can be managed in this manner. In a patient with TPP with UD after treatment with MMI, it is reasonable to attempt a trial of antihistamine before changing to another ATD.