SAT-085 - Ectopic Acromegaly Mimicking Pituitary Disease: The Role of GHRH in Diagnosis and Monitoring

Ectopic secretion of growth hormone–releasing hormone (GHRH) is a rare cause of acromegaly, accounting for less than 1% of cases. It is most often associated with neuroendocrine tumors in the lung or pancreas and may cause pituitary hyperplasia or adenomas. Due to the indolent nature of neuroendocrine tumors, it can be challenging to differentiate between ectopic acromegaly and primary pituitary disease as they can have a similar clinical presentation. Measurement of GHRH can be helpful to determine if the source is ectopic versus pituitary and can provide insight into disease activity and treatment response.

A 47-year-old woman who was previously healthy was initially referred to Oncology for management of an 8.4-cm neuroendocrine tumor of the lung (LNET). The oncologist noted that the patient had features of acromegaly, including frontal bossing and prognathism, and referred the patient to our Endocrinology clinic for further evaluation. Biochemical evaluation revealed significantly elevated growth hormone (GH) of >100 ng/mL (n 0.13-9.88 ng/mL) and insulin-like growth factor-1 (IGF-1) levels at 1,138 ng/mL (n 83-220 ng/mL). Ga-68 DOTATATE PET/CT demonstrated somatostatin receptor–avid disease in the lung lesion and increased uptake in the sella turcica. Pituitary MRI revealed a 1.7-cm sellar/suprasellar lesion suggestive of an adenoma. Given the presence of both the pituitary adenoma and pulmonary neuroendocrine tumor, we assessed GHRH levels to help determine if the acromegaly was ectopic versus pituitary. GHRH levels were elevated which was suggestive of ectopic acromegaly.

In the interval, the patient underwent external beam radiation therapy for treatment of the LNET as the tumor was deemed unresectable. Following radiation, GH and IGF-1 levels initially declined which further supported our diagnosis of ectopic acromegaly. There was a transient biochemical rise in the GH, IGF-1, and GHRH levels a few months after radiation, attributed to radiation-induced tumor necrosis and episodic GHRH release. Repeat MRI of the pituitary a few months later demonstrated interval reduction in pituitary lesion size. She was then started on octreotide LAR 20 mg monthly to help achieve further biochemical and tumor control. Several months later the patient has demonstrated symptomatic improvement with normalization of GH and GHRH levels.

This case highlights the importance of considering ectopic acromegaly in patients who present with both neuroendocrine and pituitary tumors and supports the role of GHRH measurement in complex cases. In this case, ectopic GHRH secretion caused formation of a pituitary adenoma with improvement observed following treatment of the primary tumor. Serial GHRH monitoring also provided clinically meaningful insights into disease activity and treatment response.

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