SAT-043 - A Diagnostic Pitfall: Ectopic ACTH-Dependent Cushing'S Syndrome Mimicking A Pituitary Source

Background

Cushing’s syndrome (CS) comprises a group of clinical disorders that arise from chronic excess cortisol production. The majority of individuals with Adrenocorticotropic Hormone (ACTH)-dependent CS are characterized by a pituitary adenoma. Ectopic adrenocorticotropic hormone syndrome (EAS) occurs in 12-17% of CS cases, which are non-pituitary tumors, often neuroendocrine tumors.

Case

A 41-year-old woman with a medical history of obesity, hyperlipidemia, and a non-smoker was referred for assessment of progressive hirsutism, facial acne, and oligomenorrhea. She had been asymptomatic until approximately 10 months prior. Around that time, she also reported being treated for COVID-19 with systemic steroids and complained that her cycles did not return. On examination, she had a dorsocervical fat pad, abdominal striae, and hirsutism. During follow-up visits, she also reported tunnel vision, multiple falls, and increasing fatigue.
Initial labs prolactin was normal, 5.4 ng/ml. Luteinizing Hormone (LH) < 0.2 IU/L and Follicle-Stimulating Hormone (FSH) 1.3 IU/L were low. Due to concerns about CS, further investigations were undertaken, which included an overnight dexamethasone suppression test and late-night salivary cortisol measurement, which were positive. She had a high morning cortisol level of 24.6 mcg/dL, confirming Cushing’s syndrome. Susequently 24-hour urinary free cortisol and ACTH were measured, which were significantly elevated 593.5 mcg and 219 pg/mL, respectively. Following high-dose dexamethasone suppression testing, cortisol levels were consistently elevated in the morning without suppression. The 24-hour urinary cortisol level remained elevated, but with partial suppression to 92 mcg. Similarly, ACTH remained elevated but lowered compared to the initial value. Based on the results, it was pointing towards the hypercortisolism source being the pituitary.
Magnetic Resonance Imaging (MRI) of the pituitary was done; no pituitary adenoma was seen. Hence, Computed Tomography of chest, abdomen, and pelvis for ectopic source revealed a lung nodule and hilar lymphadenopathy, suspected to be the source. The patient got biopsy of mass, which was later reported as a low-grade carcinoid tumor. Meanwhile, the patient was on mifepristone. Patient underwent surgery as definitive management, and experienced improvement in her symptoms, especially her fatigue and hair growth. Follow-up testing after surgery showed normalization of cortisol and ACTH levels.

Conclusion

This case describes a rare ectopic ACTH–dependent Cushing’s from a pulmonary carcinoid, where labs misleadingly suggested a pituitary source higlighting to always consider ectopic causes. Interestingly, the timing of prior steroid use raises the possibility that it may have unmasked the tumor.

Acknowledgement
Authors acknowledge the use of ChatGPT for assistance with paraphrasing.

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