Diagnosis of cyclic Cushing's disease manifests as early morning hyperglycemia in a patient with previously well-controlled type 1 diabetes

Background Cyclic Cushing's disease (CCD) is reported to occur in approximately 15% of patients with Cushing's disease (CD). CCD is a rare phenomenon in children. Case presentation A Portuguese female with well-controlled type 1 diabetes (T1DM) on an insulin pump developed transient uncontrolled blood sugar every morning. Increased basal and bolus insulin dosing was ineffective in lowering blood sugar and she began to miss school because of nausea, vomiting, fatigue, but no ketoacidosis. Therefore, other causes of sporadic hyperglycemia were explored. Multiple 6-h urinary free cortisol (UFC) samples revealed a spike in cortisol coincident with severe hyperglycemia. Pituitary magnetic resonance imaging (MRI) revealed a 3.5 mm microadenoma and inferior petrosal sinus sampling of adrenocorticotropic hormone (ACTH) after corticotropin releasing hormone (CRH) stimulation confirmed ACTH-dependent CD. Endoscopic endonasal tumor resection led to resolution of early morning hyperglycemia and symptoms. Discussion Our case illustrates an atypical presentation of CCD. There are no previous case reports of a pediatric patient with T1DM and CCD. Unexplained hyperglycemia in a patient with previous well-controlled T1DM should prompt assessment of other causes. CCD can be easily be missed if timed 6-h UFC measurements are not obtained.