Cortisol and Phosphate Homeostasis: Cushing's Syndrome Is Associated With Reversible Hypophosphatemia

Cushing's disease and bone

Bone impairment associated with Cushing's disease (CD) is a complex disorder, mainly involving deterioration of bone quality and resulting in an increased fracture rate, often despite normal bone mineral density. Bone complications are common in patients with CD at the time of diagnosis but may persist even after successful treatment. There is currently no agreement on the optimal diagnostic methods, thresholds for anti-osteoporotic therapy and its timing in CD. In this review, we summarize the current data on the pathophysiology, diagnostic approach and management of bone complications in CD.

New insights into the vitamin D/PTH axis in endocrine-driven metabolic bone diseases

BACKGROUND

Endocrine regulation of bone metabolisms is the focus of the "Skeletal Endocrinology" series of meetings.

AIMS

To report on the outcome of the discussion on the role of vitamin D/PTH axis in endocrine osteopathies held during the 10th Skeletal Endocrinology Meeting which took place in Stresa (Italy) in March 2023.

OUTCOMES

Vitamin D/PTH axis has relevant influence on several outcomes in the general population and in patients affected by endocrinopathies such as hypoparathyroidism and secreting pituitary adenomas.

CONCLUSIONS

Assessing the status of the vitamin D/PTH axis and using vitamin D and PTH as therapeutic agents is mandatory in several endocrine-related bone metabolic conditions.

A case of hypophosphatemia and elevated intact fibroblast growth factor 23 levels after short-term saccharated ferric oxide administration in a young woman and database analysis of adverse drug reactions in Japan

Intravenous iron replacement therapy is a common treatment for iron deficiency. Commonly used agents in this treatment include ferric carboxymaltose, ferric derisomaltose, and saccharated ferric oxide (SFO). These drugs are known to elevate fibroblast growth factor 23 levels, resulting in hypophosphatemia, but in past reports, hypophosphatemia attributable to SFO treatment has been associated mainly with prolonged administration over several weeks. The present study details our experience of a case of moderate hypophosphatemia (<2 mg/dL) in a 22-year-old woman who had no specific history of hypophosphatemia during the first 5 days of SFO treatment, and showed an increase in intact fibroblast growth factor 23 levels within the first week of treatment. Cases of hypophosphatemia have been reported as occurring as early as 1 week after the start of SFO administration in the Japanese Adverse Drug Event Report database. These cases, along with our case, underline the need for awareness of the possibility of hypophosphatemia from the early stage of SFO administration, regardless of the patient's age or dosage, as well as the need to monitor patients to prevent complications.

Nomogram for predicting early hypophosphatemia in term infants

BACKGROUND

Physiological processes rely on phosphate, which is an essential component of adenosine triphosphate (ATP). Hypophosphatasia can affect nearly every organ system in the body. It is crucial to monitor newborns with risk factors for hypophosphatemia and provide them with the proper supplements. We aimed to evaluate the risk factors and develop a nomogram for early hypophosphatemia in term infants.

METHODS

We conducted a retrospective study involving 416 term infants measured serum phosphorus within three days of birth. The study included 82 term infants with hypophosphatemia (HP group) and 334 term infants without hypophosphatemia (NHP group). We collected data on the characteristics of mothers, newborn babies, and childbirth. Furthermore, univariate and multivariate logistic regression analyses were performed to identify independent risk factors for hypophosphatemia in term infants, and a nomogram was developed and validated based on the final independent risk factors.

RESULTS

According to our analysis, the multivariate logistic regression analysis showed that male, maternal diabetes, cesarean delivery, lower serum magnesium, and lower birth weight were independent risk factors for early hypophosphatemia in term infants. In addition, the C-index of the developed nomogram was 0.732 (95% CI = 0.668-0.796). Moreover, the calibration curve indicated good consistency between the hypophosphatemia diagnosis and the predicted probability, and a decision curve analysis (DCA) confirmed the clinical utility of the nomogram.

CONCLUSIONS

The analysis revealed that we successfully developed and validated a nomogram for predicting early hypophosphatemia in term infants.

Clinical features and risk factors for postoperative recurrence in patients with Cushing's syndrome of different etiologies

The clinical characteristics of Cushing's syndrome (CS) vary with etiology, and few studies have investigated the risk factors affecting CS recurrence after surgery. This retrospective study involved 202 patients diagnosed with CS between December 2012 and December 2022. The patients were divided into three groups according to etiology: Cushing's disease (CD), adrenocortical adenoma (ACA), and ectopic adrenocorticotropic hormone (ACTH) syndrome (EAS). Of the patients with CS, 41.9% had hypokalemia and 15.0% had hypophosphatemia. The cortisol levels were negatively correlated with blood potassium, blood chlorine, and blood phosphorus. Moreover, 22.4% of patients had an abnormal heart structure, 11.2% had centripetal remodeling, 5.6% had centripetal hypertrophy, and 5.6% had centrifugal hypertrophy. The overall recurrence rate of CS caused by pituitary tumors and adrenal adenoma was 25.7%. The recurrence times were longer in the ACA group versus the CD group, in patients < 50 years of age versus in patients ≥ 50 years old group, and in patients with CD with tumors ≥ 1 cm versus tumors < 1 cm. Age, preoperative cortisol level, postoperative cortisol level, and absolute neutrophil value were closely related to postoperative recurrence, and etiology was an independent predictor of tumor recurrence in patients with CS. The results of this study showed that CS caused by different etiologies showed different clinical manifestations, blood electrolyte characteristics, and that CS could affect patient cardiac structure and function. Etiology is an independent predictor of tumor recurrence in patients with CS.

Case Report: Unexplained Mild Hypophosphatemia and Very High Serum FGF23 Concentrations

Fibroblast growth factor (FGF)23 is one of the major regulators of phosphate homeostasis. Hypophosphatemia can lead to muscle weakness, fatigue, and osteomalacia. In the setting of hypophosphatemia, serum FGF23 can be measured to differentiate between FGF23-mediated and non-FGF23-mediated renal phosphate wasting. C-terminal FGF23 (cFGF23) assays detect both cFGF23 and intact FGF23 (iFGF23). Circulating FGF23 is regulated by 1.25-dihydroxy-vitamin D, parathyroid hormone (PTH), serum phosphate, and serum calcium but also by, for example, iron status, inflammation, erythropoietin, and hypoxia-inducible-factor-1-α. We present the case of a 48-year-old woman with unexplained mild hypophosphatemia, very high cFGF23, and normal iFGF23. The patient proved to have an iron deficiency. Iron deficiency alters the iFGF23-to-cFGF23 ratio. After initiation of iron treatment, cFGF23 strongly decreased. This case report illustrates the limitation of cFGF23 assays and urges clinicians to be aware that cFGF23 concentrations do not necessarily reflect iFGF23 concentrations and that alternative causes for its elevation should be considered (eg, iron deficiency). © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.

Hypophosphatemia in Patients With Multiple Myeloma

Hypophosphatemia is among the most common electrolyte abnormalities, especially among patients with underlying malignancies, and is frequently associated with adverse prognoses. Phosphorus levels are regulated through a number of mechanisms, including parathyroid hormone (PTH), fibroblast growth factor-23 (FGF-23), vitamin D, and other electrolyte levels themselves. Clinically, the findings are nonspecific, and the diagnosis is frequently delayed. This article is a narrative literature review. The PubMed database was searched for relevant articles pertaining to hypophosphatemia causes and consequences in patients suffering from multiple myeloma. We found a variety of causes of hypophosphatemia in patients with multiple myeloma. Tumor-induced osteopenia, although more common among patients with small squamous cell carcinomas, can occur with multiple myeloma as well. Additionally, both light chains themselves and medications can trigger Fanconi syndrome, which leads to phosphorus wasting by the kidney. Bisphosphonates, in addition to being a possible cause of Fanconi syndrome, lead to a decrease in calcium levels, which then stimulates parathyroid hormone (PTH) release, predisposing the patient to significant hypophosphatemia. Additionally, many of the more modern medications used to manage multiple myeloma have been associated with hypophosphatemia. A better understanding of those mechanisms may give clinicians a clearer idea of which patients may need more frequent screening as well as what the potential triggers in the individual patient may be.

Phototherapy-induced hypocalcemia and hypoparathyroidism in icteric term newborns

OBJECTIVES

Phototherapy is demonstrated to cause hypocalcemia by decreasing melatonin levels and increasing cortisol levels. However, the relationship between parathyroid hormone (PTH) level and calcium has not been previously evaluated in patients receiving phototherapy. Our study aimed to evaluate the effect of phototherapy on ionized calcium (iCa), total calcium (tCa), corrected calcium (cCa), magnesium (Mg), phosphorus (P), 25-hydroxyvitamin D (25(OH)D), and PTH levels.

METHODS

Infants who were born at term and received inpatient phototherapy for indirect hyperbilirubinemia were included in our study. The patients' gestational age, birth weight, and phototherapy durations were recorded. Total bilirubin, albumin, iCa, tCa, cCa, Mg, 25(OH)D, and PTH levels before and after phototherapy were compared. Laboratory results were also compared between patients who received phototherapy for ≤24 h, 25-47 h, and ≥48 h.

RESULTS

A total of 166 term infants were included in the study. The mean duration of phototherapy was 31.9 ± 9.2 h. Albumin levels before and after phototherapy were similar (p=0.246). However, there were significant decreases in iCa, tCa, cCa, Mg, 25(OH)D, and PTH levels after phototherapy (p<0.001), while P level was significantly increased after phototherapy (p<0.001). In addition, P levels increased with >24 h of phototherapy, while iCa, tCa, cCa, Mg, 25(OH)D, and PTH levels decreased significantly with ≥48 h of phototherapy (p=0.002, p=0.008, p=0.001, p=0.012, and p<0.001, respectively).

CONCLUSIONS

This study demonstrates that PTH suppression is one of the causes of phototherapy-induced hypocalcemia.