(13.15) Overt Acromegaly Secondary to Pituitary Microadenoma

With an annual incidence of 4.6 cases per 1 million people, acromegaly remains a rare disease with significant impact on patient’s lives. At diagnosis, most patients have pituitary macroadenomas (≥1cm) with some adenomas showing suprasellar extension. We are reporting a patient with classical features of acromegaly caused by a sub centimeter pituitary tumor. 

Case(s) Description :

A 44-year-old man presented to endocrine clinic with >10 years of progressive weight gain. Prior obesity evaluation in 2017 was notable for hypogonadotropic hypogonadism that was treated with testosterone and an elevated IGF-1 at 431 ng/mL (83-233 ng/mL). His IGF-1 level remained elevated at 487 ng/mL in 2018. Treatment however remained focused on his obesity and hypogonadism. Pituitary MRI  in 2018, obtained for an incidental finding of possible empty sella on a neck CT, was unremarkable and showed no evidence of pituitary abnormality. Our evaluation included repeat testing of his pituitary hormones with low testosterone, inappropriately normal LH/FSH, a normal prolactin level, and persistently elevated IGF-1 level of 533 ng/mL. Between 2017 and 2023 he was diagnosed with hypertension, obstructive sleep apnea, and pre-diabetes. Patient also reported an increase in ring size from 10 to 15 and in shoe size from 12 to 14, gapping of his teeth, malodorous hyperhidrosis, severe night sweats, severe hip and knee osteoarthritis, and development of numerous skin tags. X-rays of hands and heels also showed changes consistent with acromegaly. He had no visual field defects or headaches. Oral glucose tolerance testing failed to suppress his growth hormone (GH) levels (baseline 2.1 ng/mL, nadir 1.3 ng/mL) confirming autonomous secretion of GH. Sellar MRI demonstrated a 4mm pituitary microadenoma with an increased radiotracer pituitary uptake on a dotatate scan. Ectopic GHRH secretion was ruled out by a normal serum GHRH level of 6 pg/mL (5-18 pg/mL).

Discussion :

The delayed diagnosis of acromegaly is common. This case highlights some of the diagnostic challenges associated with acromegaly as initial MRI failed to identify a pituitary lesion despite elevated levels of IGF-1 and only 67 years later, a 4 mm lesion was identified. Pituitary microadenomas make up a very small portion of all GH secreting pituitary adenomas with the majority being macroadenomas at time of diagnosis. This case also highlights the inhibitory role of GH on luteinizing and follicle stimulating hormones leading to hypogonadotropic hypogonadism. Hypogonadism in pituitary adenomas is most often from mass effect on the gonadotropic cells or elevated prolactin levels. Elevated levels of GH and IGF-1, regardless of tumor size, can cause hypogonadotropic hypogonadism. Early recognition and diagnosis of acromegaly is difficult especially in the setting of a microadenoma but is paramount to preventing irreversible changes and significant complications.