Serum phosphate levels at diagnosis predict long-term risk for hypopituitarism in patients with acromegaly.

Introduction: Excess growth hormone (GH) secretion in acromegaly has a major impact on mineral balance and serum phosphate levels. However, the clinical utilization of serum phosphate levels as a marker for long-term disease outcomes in acromegaly has not been evaluated.

Methods: This is a retrospective study of patients with acromegaly who were followed in a tertiary center. Data were retrieved on patient characteristics, endocrine and biochemical evaluation, and tumor parameters. Comparisons were performed by measuring baseline phosphate levels and conducting correlation analysis and multivariable logistic regression.

Results: Sixty-one patients were followed for 4.5 years (range 1-21). Patients with hyperphosphatemia (> 4.5 mg/dl) at baseline had larger adenomas (15.0 mm [8.0, 47.0] vs. 10.0 mm [3.0, 24.0], p = 0.001), a rate chance of invasive adenoma (16 [80.0%] vs. 14 [46.7%], p = 0.02), and lower serum cortisol levels (226.0 nmol/l [27.6, 516.0] vs. 294.0 nmol/l [32.0, 610.0], p = 0.02). Baseline serum phosphate levels positively correlated with IGF-1 levels (r = 0.43, p = 0.003) and negatively correlated with morning plasma cortisol levels (r = -0.46, p = 0.002). Regarding long-term impact, baseline phosphate levels correlated with the number of pituitary axes involved 6 months after diagnosis (r-0.34, p = 0.01). In multivariable analysis, baseline plasma phosphate levels were independently associated with risk for disease progression/recurrence (odds ratio [OR] 9.66, 95% confidence interval [CI] 1.5, 105.9, p = 0.03) and for invasive adenoma (OR 6.21, 95% CI 1.6, 28.7, p = 0.01).

Conclusion: Elevated pretreatment serum phosphate levels are associated with a greater risk of disease persistence and recurrence and with altered pituitary function in patients with acromegaly.