A Rare Case of Ectopic Adrenocorticotropic Hormone Syndrome (EAS) in an Adolescent Girl With a Thymic Neuroendocrine Tumour

In adults, Cushing's syndrome (CS) caused by tumours that produce adrenocorticotropic hormone (ACTH) outside of the pituitary gland is quite prevalent. However, it is uncommon in children and teenagers. Ectopic ACTH syndrome (EAS) is a rare occurrence in young children, accounting for less than 1% of cases. Nevertheless, when it does occur, it tends to be a severe condition due to the profound hypercortisolism that can occur independently of the tumour. Consequently, EAS should be regarded as a critical endocrine emergency, necessitating prompt action in terms of diagnostic procedures and therapeutic interventions. A 14-year-old White female from the United Kingdom (UK) presented with a two-week history of hands and feet swelling, accompanied by a non-itchy rash on the face, back, and chest for one week. Initial investigations revealed hypokalemic alkalosis, hyperglycaemia, elevated serum and 24-hour urinary cortisol, and high ACTH level. Further investigations confirmed EAS, and to find out the primary tumour location, a contrast-enhanced thoracic CT scan was done and identified a 5x3 cm mass with enhanced thymic shadow. Increased radioactivity uptake in the left upper chest along with widespread GAD-avid metastatic disease unveiled by Gallium-DOTA-TATE PET scan. An abdominal MRI, detecting multiple liver deposits, prompted a liver biopsy, revealing a malignant tumour with neuroendocrine differentiation. The patient was diagnosed with EAS with a primary neuroendocrine tumour of the thymus and metastasis. This case underscores the significance of considering EAS in patients with a diagnosis of CS, especially in young individuals with no known risk factors.