Thyroiditis: A Rare Manifestation of Enasidenib-Induced Differentiation Syndrome.

Enasidenib is an FDA-approved isocitrate dehydrogenase 2 (IDH2) inhibitor, which is used in the treatment of acute myeloid leukemia (AML). We present a case of AML with an IDH2 mutation treated with a regimen of enasidenib and 5-azacitidine, where thyroiditis was noted to be a part of differentiation syndrome. The patient is a 77-year-old woman with IDH2-mutated AML who had initially been started on 100 mg of enasidenib and then presented with dyspnea and was diagnosed with pleural effusion - a common presentation with enasidenib - but was also noted to have thyroiditis. She was started on steroids, but due to continued hyperbilirubinemia and thyroiditis, her dose of enasidenib was reduced to half, which resulted in clinical improvement. This case demonstrates thyroiditis as one of the rare manifestations in the treatment of AML with enasidenib-induced differentiation syndrome.