Introduction: Cystic fibrosis (CF) is an autosomal recessive disorder caused by mutations in the CFTR gene. Complications such as cystic fibrosis–related diabetes (CFRD) are well recognized. The association between CF and autoimmune thyroid disease, however, is rare and poorly understood. We report a case of CFRD complicated by Graves’ disease. Case: A 22-year-old male was diagnosed with CF at age 5, confirmed by a positive sweat chloride test. Following the diagnosis, lifelong pancreatic enzyme replacement therapy (Creon) was initiated to treat exocrine pancreatic insufficiency. In 2021, he developed type 3c diabetes, attributed to endocrine pancreatic insufficiency, and required regular basal insulin therapy. In early 2024, he developed hypokalemic periodic paralysis with proximal myopathy, despite potassium correction, and was admitted to the hospital. On admission, examination revealed a fine tremor and diffuse bilateral neck swelling. Biochemical evaluation showed thyrotoxicosis with Free T4 of 37 pmol/L and thyroid-stimulating hormone (TSH) <0.01 mIU/L. He started a tapering dose of carbimazole and propranolol. An urgent neck ultrasound showed a heterogeneous thyroid parenchyma with increased vascularity and no nodules. Elevated anti-thyroid peroxidase (anti-thyroid peroxidase, >600 IU/mL) and TSH receptor antibodies (thyrotropin receptor antibody, 2.57 IU/L) confirmed a diagnosis of Graves’ disease. During follow-ups, he had issues with compliance with the antithyroid therapy. However, the latest thyroid function test in February 2026 showed Free T4 of 20.5 pmol/L with suppressed TSH of <0.01 mIU/L. He remains clinically euthyroid throughout the follow-up. Conclusion This case highlights a rare but clinically relevant coexistence. Clinicians managing symptomatic CF patients should vigilantly screen for thyroid dysfunction to ensure early diagnosis and timely intervention. Early recognition and treatment may improve patient outcomes. Further research is needed to clarify the immunological link between CF and autoimmunity.
Cystic Fibrosis ; Graves Disease