25-OH vitamin D levels in patients with pituitary adenoma

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INTRODUCTION
Pituitary adenomas are most common in the 3 rd decade and constitute 10% of all intracranial neoplasms (Gsponer et al., 1999;Saeger et al., 2007;Freda, 1999).Pituitary adenomas are classified according to the size and function of the cell in which they originate (Snyder, 2001).Functional pituitary adenomas may be disorders affecting bone metabolism.This condition was described in Cushing's disease.Vitamin D has an important clinical role due to its relationship with calcium balance and bone metabolism.This degree of vitamin D deficiency may contribute to the development of osteoporosis and the risk of fracture and fall (Forrest and Stuhldreher, 2011).
The aim of this study was to evaluate vitamin D levels in pituitary adenomas.

MATERIALS AND METHODS
The study included 88 patients (60 females and 28 males) who were followed for pituitary adenoma between the years of 2016 to 2018.Patients' physical examination, pituitary MR results, FSH, LH, estradiol, testosterone, ACTH, cortisol, growth hormone, Igf-1, prolactin and 25-OH vitamin D levels results were recorded.1 mg dexamethasone test was performed in appropriate patients.
Prolactin has an adverse effect on bone metabolism by inhibiting osteoblast proliferation and increasing osteoclytic activity.Prolactin also causes an increase in RANKL and osteoprotogerin.As a result, bone loss is observed.In women with prolactinoma, approximately 25% of the vertebrae are lost due to hypogonadism.Treatment with bone density increases, but may not return to the old level.In men with prolactinoma, osteopenia / osteoporosis occur due to low testosterone levels (Greenspan, 1986;Vartej et al., 2001;Mazziotti et al., 2015Mazziotti et al., , 2011)).
The pathogenesis of osteoporosis in patients with Cushing's disease decreased osteoblast function, calcium absorption from the bowel, calcium excretion from kidneys, gonadal steroid synthesis, muscle mass and strength, and growth hormone secretion.In Cushing's disease, osteoporosis was found in 50% of the patients.Even in these patients, non-traumatic fractures or osteoporosis incompatible with age was detected (Kaltsas et al., 2002;Mancini et al., 2004;Minetto et al., 2004;Mirza and Canalis, 2015).In acromegalic patients, growth hormone stimulates the carboxylation of osteocalcin on the one hand and the production of RANKL and osteoprotoger.Growth hormone and IGF-1 stimulate the 1-alpha hydroxylase enzyme in the kidney to increase the synthesis of 1, 25 dihydroxycholecalciferol.Even if osteoporosis does not increase in acromegalic patients, the risk of bone fracture increased (Giustina et al., 2008;Madeira et al., 2013;Wassenaar et al., 2011;Anthony, 2014).
Vitamin D deficiency and / or insufficiency were found in all patients in this study.In addition to existing pathophysiological conditions we opined that vitamin D deficiency increases the risk of osteoporosis and / or bone fracture in these patients.

Conclusion
Vitamin D deficiency should be considered and treated in these patients with high risk of ostoporosis or high risk of bone fractures when treating these patients.

Figure 1 :
Figure 1: 25-OH vitamin D levels by gender in pituitary adenoma cases.