Case Report: ACTH-independent Cushing's syndrome caused by isolated micronodular adrenal disease in a 23-month-old girl.

Cushing's syndrome in early childhood is rare and may be particularly challenging to diagnose when adrenal imaging is unrevealing. We report the case of a 23-month-old girl who presented with rapid weight gain, cushingoid appearance, hypertrichosis, severe hypertension, irritability, and developmental regression. Biochemical assessment confirmed adrenocorticotropic hormone (ACTH)-independent hypercortisolism, with suppressed ACTH, loss of circadian cortisol rhythm, lack of cortisol suppression following dexamethasone administration, and increased 24-hour urinary free cortisol excretion. Adrenal magnetic resonance imaging showed morphologically normal adrenal glands. Adrenal computed tomography was not performed, to avoid additional ionising radiation after a non-diagnostic adrenal MRI in a 23-month-old child. Adrenal scintigraphy with ¹³¹I-NP-59 after metyrapone-induced suppression demonstrated bilateral adrenal uptake, slightly more prominent on the right. The patient underwent right adrenalectomy. Histopathological examination showed micronodular adrenocortical hyperplasia without pigmentation, atypia, or malignant features, consistent with isolated micronodular adrenal disease. Following surgery, blood pressure, metabolic abnormalities, cutaneous manifestations, and motor function improved markedly. Steroid supplementation was required for only 3 days post-operatively, with no evidence of persistent adrenal insufficiency. At 3 years of follow-up, there were no clinical features of recurrent hypercortisolism, blood pressure remained normal without antihypertensive therapy, body mass index had markedly improved, and available biochemical parameters were reassuring. This case highlights that isolated micronodular adrenal disease should be considered in very young children with ACTH-independent Cushing's syndrome even when adrenal magnetic resonance imaging is normal. Functional adrenal imaging may be useful in selected cases, and unilateral adrenalectomy may achieve durable remission while delaying permanent adrenal insufficiency.