Background: A persistent hyperphosphataemia represents one of the most important factors in the development of secondary hyperparathyroidism (sHPTH). The present prospective study was designed in order to test the hypothesis that a higher body mass index (BMI) may predispose to a larger body burden of phosphate (P), influencing by that way the severity of sHPTH.
Methods: Histological studies were performed on 168 parathyroid glands of 42 consecutive adult Caucasian haemodialysis patients (20 males and 22 females) referred for first parathyroidectomy (PTx): each parathyroid gland was graded as 0, when only or mainly diffuse hyperplasia was found, or as 1, when only or mainly nodular hyperplasia was found. Thus, parathyroid histology was scored on a 5-point scale: 0 = diffuse hyperplasia in the four glands; 1 = nodular hyperplasia in one gland; 2 = nodular hyperplasia in two glands; 3 = nodular hyperplasia in three glands; 4 = nodular hyperplasia in the four glands. For sake of simplicity, the three less severe histological gradings, i.e. scores 0-2 were grouped together and indicated as score group 2.
Results: The distribution of the patients was the following: 28.6% were in the score group 2, 23.8% in the score group 3 and 47.6% in the score group 4 (20 patients, 14 of whom were females). The output of the one-way ANOVA with the histological scores as grouping variable and age, dialysis duration, BMI and pre-PTx serum iPTH, alkaline phosphatase (ALP), calcium (Ca) and P as predictors showed that only BMI was different among the three histological scores (P = 0.001). By stratifying the analysis by gender, the relationship between BMI and histological scores was confirmed only in females (P = 0.006). The stratification of the entire cohort into two groups according to the cut-off value of BMI = 25 kg/m(2) showed that: (i) score 4 was more prevalent in the high-BMI group and score 2 in the normal-BMI group (P = 0.01); (ii) female gender was more represented in the high-BMI group (12 out of 18 patients, P = 0.04); and (iii) the pre-PTx serum P levels were significantly higher in the high-BMI group (P = 0.008). The output of the linear multiple regression analysis with pre-PTx serum P as dependent variable and BMI, pre-PTx serum ALP and Ca as independent variables (selected according to the statistical significance in the bivariate correlations) showed that only serum Ca and BMI were statistically significant predictors of serum P levels.
Conclusions: A high BMI and female gender are associated with an increased risk of nodular hyperplasia of parathyroid glands in adult Caucasian haemodialysis patients. The two risk factors, above all if combined in the same patient, appear to predispose to a larger body burden of P, increasing by that way the severity of sHPTH.