Introduction: Autoimmune thyroid disease can follow a triphasic course: thyrotoxicosis, a transient euthyroid period, and eventual hypothyroidism, and may coexist with myelodysplastic syndrome (MDS) in the context of immune dysregulation. Case: We describe a 35-year-old male with MDS (multilineage dysplasia) receiving cyclosporine who initially presented with painless thyrotoxicosis, with suppressed thyroidstimulating hormone (TSH) and elevated free thyroxine (FT4). During this hyperthyroid phase, thyrotropin receptor antibody (TRAb) was positive. Over time, his thyroid status fluctuated, progressing to overt hypothyroidism, and he had poor adherence to thyroid medications. On admission, he had prominent hypothyroid features (fatigue, cold intolerance, slowed movement, periorbital puffiness) with severe biochemical hypothyroidism (TSH 49.5 µIU/mL; FT4 0.419 ng/dL). Anti-thyroid peroxidase (anti-TPO) antibodies 12.62 IU/mL (negative <5.61 IU/mL; positive ≥5.61 IU/mL) showed an autoimmune response to the thyroid. Thyroid ultrasound showed heterogeneous, hyperechoic with some hypoechoic parts, and no significant increase in thyroid vascularity was observed, supporting autoimmune thyroiditis representation. His hematologic profile remained consistent with MDS, with chronic macrocytic anemia and thrombocytopenia. Conclusion This case highlights a dynamic autoimmune thyroiditis phenotype progressing from a hyperthyroid phase with TRAb positivity to higher anti-TPO overt hypothyroidism in a patient with MDS. In individuals with MDS and changing thyroid function tests, clinicians should keep autoimmune thyroiditis variants in mind and use thyroid antibodies together with ultrasound to secure the diagnosis when the clinical pattern is typical.
Myelodysplastic Syndromes ; Thyroiditis, Autoimmune ; Hypothyroidism ; Thyrotoxicosis