Mineral and bone disorders in peritoneal dialysis

Abstract

Introduction

Disorders of mineral and bone metabolism are common in dialysis patients and are responsible for an increased risk of fracture, cardiovascular risk and mortality. The mineral and bone disorder most frequently found in peritoneal dialysis (PD) is adynamic osteopathy. The aim of our work is to describe the mineral and bone profile of patients on peritoneal dialysis, to determine the prevalence of hyperparathyroidism in this population and to identify the risk factors associated with it.

Material and method

This is a cross-sectional study including all our PD patients in whom we analyzed the various clinical, biological, radiological and therapeutic data related to mineral and bone metabolism.

We defined hyperparathyroidism by a parathyroid hormone (PTH) ≥ 600pg/ml and we determined the risk factors by comparing two groups : with and without hyperparathyroidism.

Results

We retained 85 patients whose mean age was 49.18 ± 17.28 years and the sex ratio of 0.77. The seniority in dialysis was 33.31 ± 26.68 months. Median PTH was 668 pg/ml [34-3800] with serum calcium at 87.75±7.52 mg/l, phosphatemia at 54.07±16.69 mg/l and vitamin D at 23.74±11.56 ng/ml. Hyperparathyroidism was found in 60% of patients.

The risk factors for hyperparathyroidism noted in our study are: seniority in PD, high PTH before the start of dialysis, and hyperphosphatemia. The short medical follow-up before dialysis seems to play an important role in the development of secondary hyperparathyroidism.

Conclusion

Hyperparathyroidism is the most frequent mineral and bone disorder in our series. Factors correlated with hyperparathyroidism are length of time on dialysis, hyperphosphatemia and high parathormone levels before the start of dialysis.

Peritoneal Dialysis (PD) is a substitute technique for chronic end-stage renal failure, complementary to hemodialysis and renal transplantation.

Disorders of mineral and bone metabolism are common in dialysis patients and are responsible for an increased risk of fracture, cardiovascular risk, and mortality. Indeed, numerous studies have demonstrated these disorders, and more specifically those linked to hyperparathyroidism, are responsible for extra-skeletal calcifications, in particular vascular and valvular[1];[2];[3], and are implicated in the pathogenesis of left ventricular hypertrophy[4], thus increasing cardiovascular risk and the risk of morbidity and mortality[5].

Unlike hemodialysis, the mineral and bone disorder most frequently found in PD is adynamic osteopathy rather than secondary hyperparathyroidism. The absence of data concerning mineral and bone disorders in the Moroccan population on PD encouraged us to study this subset in order to compare our results with data from the literature.

The aim of our work is to:

- Describe the mineral and bone profile of our patients on PD.

- Determine the prevalence of different mineral and bone disorders in our population.

- Identify the risk factors associated with hyperparathyroidism in our patients on PD.

MATERIAL AND METHODS

We conducted a descriptive and analytical monocentric cross-sectional study in the PD unit of the nephrology department of the Academic Hospital Ibn Sina in Rabat (Morocco). We included all prevalent patients on peritoneal dialysis with a duration of PD greater than 3 months.

An operating sheet has been drawn up to study the following parameters:

1 – Demographic and clinical characteristics:

• Age and sex.

• Comorbidities (arterial hypertension (HTA), diabetes).

• Initial nephropathy.

• The duration of medical follow-up at the stage of chronic renal failure (CRI) stages 4 and 5 before starting dialysis.

• Seniority in dialysis.

• The modality of PD.

• The quality of purification (Kt/v and weekly creatinine clearance).

• Clinical symptoms, namely bone pain, arthralgia, and pathological fractures.

2 – Biological parameters related to mineral and bone disorders:

These parameters were recorded on the basis of an average of the last 3 months:

• Calcemia, phosphatemia, vitamin D2-D3 levels, alkaline reserve, alkaline phosphatase.

• The parathormone level (PTH 1-84) before the start of dialysis, 3 months after the start of it, at 1 year, and the current PTH level. The parathormone assay is a micro-particle immunoassay by chemiluminescence on a blood sample in a dry tube.

3 – Radiological parameters:

• X-rays of the skeleton—namely X-rays of the skull in profile, of the hands, and of the pelvis—in search of the impact of mineral and bone disorders.

• X-rays of the lateral chest or pelvis looking for aortic or iliac vascular calcifications.

• Cervical ultrasound to look for parathyroid nodules or parathyroid hyperplasia.

• Transthoracic echocardiography looking for valve calcifications.

4 – Therapeutic and evolutionary parameters:

This medical treatment consists of calcium chelators of phosphorus, the most widely used of which is calcium carbonate, non-calcium chelators of phosphorus and vitamin D in its two native and active forms, and calcimimetics. Vitamin D3 (cholecalciferol) is administered according to the protocol of our service, which consists of an attack treatment of 3 doses of 100,000 IU spaced one week apart in the event of a vitamin-D deficiency with a level below 15 ng/ml or spaced 2 weeks apart in the event of a vitamin-D deficiency with a rate between 15 and 30 ng/ml. The maintenance treatment is 25,000 IU per week. Our therapeutic target for vitamin D3 is 40 ng/ml. Active vitamin D (alfacalcidol) is prescribed in cases of secondary hyperparathyroidism without hypercalcemia or hyperphosphatemia. Surgical treatment consists of a 7th/8th parathyroidectomy indicated in the presence of symptomatic hyperparathyroidism with hypercalcemia and/or hyperhposphatemia.

We defined hyperparathyroidism by a parathyroid hormone (PTH) greater than or equal to 600 pg/ml, i.e., 9 times the normal PTH value, according to the Kidney Disease Improving Global Outcomes (KDIGO) recommendations. To determine the risk factors for hyperparathyroidism, we defined two groups: group A having a parathormone greater than or equal to 600 pg/ml (PTH ≥ 600 pg/ml) and group B whose parathormone is strictly lower, at 600 pg/ml (PTH < 600 pg/ml).

Hypoparathyroidism was defined by a PTH less than 60 pg/ml.

The various data collected were analyzed using the statistical analysis software SPSS version 20 with the help of a statistician. The results were expressed in numbers and percentages for the qualitative variables. For the quantitative variables, the results were expressed either as a mean and standard deviation for the variables with a symmetrical distribution or as a median for the variables with an asymmetrical distribution. The comparison of our two groups of patients, that with PTH ≥ 600 pg/ml and that with PTH < 600 pg/ml, was made using the one-factor Anova test, and the variables were checked using the tests of Student and Chi-square. Multivariate analysis was done using the Manova test. A value of p < 0.05 was considered significant.

I. Characteristics of our population of peritoneal dialysis patients

We identified 85 patients meeting our inclusion criteria whose mean age was 49.18 ± 17.28 years, with extremes of 13 and 86 years. The sex ratio was 0.77, with a female predominance of 56.5% (n=48).

Chronic renal failure is third to diabetes in 17.6% of cases and to nephro-angiosclerosis in 11.8% of cases. The initial nephropathy remains undetermined in 28 patients (32.9%). Other etiologies of renal failure are summarized in

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