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Neuroendocrinology and Pituitary

MON-037 - Distinguishing Primary Hyperparathyroidism from IGF-I-Induced Changes in Calcium and Phosphate Metabolism in Acromegaly using Routine Biochemical Markers.

Monday, June 15, 2026
9:00 AM - 2:00 PM CT
Location: ENDOExpo; Poster Floor
Disclosure(s):
Christa Flueck, MD: No financial relationships to disclose


Background: Acromegaly is frequently associated with disturbances in calcium–phosphate metabolism, including mild hypercalcemia. These biochemical changes complicate the assessment of parathyroid function in a clinical context where the prevalence of primary hyperparathyroidism (PHPT) is increased among patients with acromegaly (approximately 6·0%). Although the coexistence of acromegaly and PHPT may occur as part of multiple endocrine neoplasia, most reported cases arise in individuals without identifiable pathogenic variants in MEN1 or other predisposing genes. We aimed to refine the diagnosis of PHPT in acromegaly by integrating serum calcium, phosphate, and PTH concentrations into a classification model.

Methods: We conducted a retrospective diagnostic study (CEEI/IRB00003888) at two university hospitals in France. Adult patients with acromegaly evaluated between January 2013 and December 2024 were included. Eligible patients had at least one serum calcium measurement obtained while acromegaly was biochemically uncontrolled. Patients with isolated acromegaly were compared cross-sectionally with those diagnosed with PHPT. Diagnostic models were developed using support vector machine (SVM) algorithms.
Findings: A total of 396 patients with acromegaly were included, of whom 212 (54%) were women. Median age at evaluation was 43.5 years [IQR 33–55], and median IGF-I concentration was 467 ng/mL [IQR 322–655]. Isolated acromegaly was present in 372 patients (93·9%); among these, hyperphosphatemia occurred in 138 (37·1%) and mild hypercalcemia in 12 (3·2%), all resolving after effective treatment of acromegaly. Twenty-four patients (6·1%) had acromegaly with PHPT. All but one exhibited mild hypercalcemia (median serum calcium 2·72 mmol/L [IQR 2·66–2·86]) with elevated PTH and low-to-normal serum phosphate. No pathogenic variants in MEN1 or other tested genes were identified. Eleven patients underwent less-than-subtotal or subtotal parathyroidectomy, with normalization of serum calcium in all cases. A SVM-derived model incorporating serum calcium, phosphate, and PTH correctly classified 220 of 221 patients with complete data (99·5%; 95% CI 98·7–100). A simplified model including calcium and phosphate correctly classified 384 of 386 patients with available measurements (99·5%; 95% CI 98·8–100), with no difference in diagnostic performance between models.
Interpretation: These findings provide a practical diagnostic tool to refine the biochemical evaluation of hypercalcemia in acromegaly. By distinguishing IGF-I–mediated mineral metabolism changes from true PHPT, this approach may help avoid unnecessary parathyroid surgery and inappropriate genetic testing, while ensuring timely referral for specialized surgical management in patients with PHPT.

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