Indicators of calcium-phosphorus metabolism and bone remodeling as risk factors for bone mineral density disorders in patients with rheumatoid arthritis

Abstract

Introduction. Osteoporosis (OP) is one of the most common causes of disability decrease in life expectancy among the elderly. The main risk factors for the occurrence of osteoporosis in patients with rheumatoid arthritis (RA) include family predisposition, female sex, age, the presence of menopause, chronic inflammatory process and its treatment. The current task remains the assessment of risk factors for the occurrence of OP in patients with RA, and there is also the need to assess risk factors for the occurrence of OP in patients with RA based on the results of laboratory parameters of calcium-phosphorus metabolism and markers of bone remodeling, which will improve the diagnosis of bone mineral density (BMD) disorders. The aim of the study. To determine the indices of calcium-phosphorus metabolism and bone remodeling as risk factors for the occurrence of bone mineral density disorders in patients with rheumatoid arthritis. Materials and methods. To the study were randomly enrolled 76 patients with RA (64 women (84.21%) in the premenopausal period and 12 men (15.78%) 38-60 years old (the average age at the time of examination of women – 48.67 ± 2.34 years, men – 45.42 ± 2.78). All patients were receiving methylprednisolone at a dose of 4.0 mg/day and a short course during an exacerbation up to 24.0 mg/day for RA treatment, but received no drugs for the treatment of BMD disorders. All patients underwent an assessment of BMD using ultrasound bone densitometry of the calcaneus, indicators of calcium-phosphorus metabolism and markers of bone remodeling were determined. Based on the obtained results, patients were stratified into three groups as follows: (1) 18 patients – 15 women and 3 men, aged 38-52, with RA without BMD disorders; (2) 34 patients – 31 women and 3 men, aged 38-54, with RA and osteopenia; (3) 24 patients – 18 women and 6 men, aged 41-53, with RA and OP. The control group consisted of 22 practically healthy individuals. Results. Patients with RA without BMD disorders significantly more often observed a decrease in the content of total calcium (p is less than 0.015) and ionized calcium (p is less than 0.000) in the blood serum, as well as a decrease in the individual osteocalcin (OK) index (р is less than 0.000). These patients were also endangered with reduced OC and/or total Ca in blood serum (p is less than 0.005). It was also revealed that in RA patients a decrease in urinary phosphorus indicates higher risk of osteopenia compared to RA patients with normal reference values of the same index (p is less than 0.000). Moreover, in patients with RA increased ionized calcium and decreased phosphorus indeces in urine correlated with significantly higher risk of osteoporosis compared to RA patients with these indeces normal levels (p is less than 0.050). According to the obtained data, an increase in the β-CrossLaps index in patients with RA is a risk factor for the occurrence both osteopenia and OP (p is less than 0.050). It was also founded that the reduced OC and increased ionized calcium levels can be treated as a risk factor for the occurrence of OP in patients with RA (p is less than 0.023). Conclusions. The risk of osteopenia in patients with rheumatoid arthritis without a violation of the mineral density of bone tissue is significantly higher in case of decreased content of blood serum total calcium or ionized calcium levels, or reduced osteocalcin index, or a simultaneous decreased content of total calcium and osteocalcin levels in blood serum. The risk of osteopenia in patients with rheumatoid arthritis is significantly higher if there is detected decreased phosphorus content in urine, or an increasede content of C-terminal telopeptide in blood serum, specific for the degradation of type I collagene. The risk of osteoporosis in patients with rheumatoid arthritis is significantly higher if there is a statistically significant increased level of ionized calcium in blood serum, or decreased content of phosphorus in the urine, or increased serum level of C-terminal telopeptidee, or an increased level of ionized calcium in the blood serum accompanied by a reduced level of osteocalcin. Keywords: calcium-phosphorus metabolism, bone remodeling markers, osteoporosis, osteocalcin, rheumatoid arthritis, bone mineral density.