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The Elusive Neuroendocrine Tumor: Finding the Ectopic ACTH Source 16 Years After the Diagnosis of Cushing Syndrome
Galina Smushkin1, Richard Phillips2, Guillaume Chausse3
1Department of Medicine, Division of Endocrinology, University of British Columbia, Victoria, BC V6T 1Z3, Canada.
Abstract:
Ectopic adrenocorticotropin hormone (ACTH) syndrome (EAS) accounts for the minority of cases of Cushing syndrome. Up to 20% of these cases remain occult, despite multiple imaging attempts to localize the ACTH-producing tumor. Here we describe long-term follow-up of a 41-year-old woman, with ectopic Cushing syndrome initially classified as occult due to negative localization studies, who had bilateral adrenalectomy to manage hypercortisolism. After 16 years and many computed tomography (CT) scans, magnetic resonance imaging scans, Octreoscans, and 2 exploration surgeries for false positives on imaging, the source of ectopic ACTH production was localized in the pancreas utilizing molecular imaging with gallium-68 somatostatin receptor-targeted positron emission tomography (PET)/CT and fluorine-18 fluorodeoxyglucose PET/CT. She underwent a distal pancreatectomy, and pathology confirmed a 1.7-cm well-differentiated pancreatic neuroendocrine tumor with a moderately strong reactivity to ACTH stain. This case demonstrates the utility of multiple functional imaging modalities in resolving these "cold cases" of occult ectopic Cushing syndrome and the importance of a timely management of hypercortisolism with bilateral adrenalectomy.
Insights
Occult ectopic adrenocorticotropin hormone (ACTH) syndrome was diagnosed after 16 years using advanced PET/CT imaging. A pancreatic neuroendocrine tumor was identified as the source, highlighting the importance of functional imaging in diagnosing rare endocrine disorders.
Area of Science:
- Endocrinology
- Nuclear Medicine
- Oncology
Background:
- Ectopic adrenocorticotropin hormone (ACTH) syndrome (EAS) is a rare cause of Cushing syndrome, with up to 20% of cases remaining occult despite extensive imaging.
- Diagnosing occult EAS presents significant challenges, often requiring prolonged investigation and multiple interventions.
Observation:
- A 41-year-old woman with occult EAS underwent bilateral adrenalectomy for hypercortisolism.
- Despite 16 years of follow-up, including numerous CT, MRI, Octreoscans, and two surgeries, the ACTH-producing tumor remained elusive.
- Advanced molecular imaging with Gallium-68 somatostatin receptor-targeted PET/CT and Fluorine-18 fluorodeoxyglucose PET/CT was employed for localization.
Findings:
- Molecular imaging successfully localized the ectopic ACTH source to the pancreas.
- A distal pancreatectomy revealed a 1.7-cm well-differentiated pancreatic neuroendocrine tumor with ACTH expression.
- This confirmed the tumor as the cause of the patient's ectopic Cushing syndrome.
Implications:
- This case underscores the critical role of advanced functional imaging modalities in resolving challenging cases of occult ectopic ACTH syndrome.
- It highlights the diagnostic utility of somatostatin receptor and FDG PET/CT in identifying elusive neuroendocrine tumors.
- Timely management of hypercortisolism, including bilateral adrenalectomy when necessary, remains crucial for patient outcomes.
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