In this study, we have found that patients with PA have a ten-fold higher prevalence of CKD at diagnosis and a higher risk of progressive kidney function impairment during follow-up than EH controls matched by age, sex, and blood pressure levels. Moreover, the prevalence of ischemic heart disease was six times higher in PA patients.
We found a prevalence of CKD more than ten times greater in patients with PA than controls. Similar results have been reported previously (14–17), and it is consistent with the harmful effects documented not only on the cardiovascular system but also on kidney function in long-standing PA (18)(19). Several clinical studies have reported possible kidney abnormalities such as proteinuria and decreased GFR in relation to plasma aldosterone concentration regardless of other known risk factors (14)(15). Often this damage is masked until the treatment of PA is performed (20). Elevated aldosterone levels have been suggested to cause glomerular hyperfiltration, which explains the decrease in GFR after treatment, and the severity of excess aldosterone in the pretreatment period seems to be the most important risk factor for deterioration of the renal function (18)(17)(21). This decrease is greater in patients with PA than in those with EH after the initiation of antihypertensive treatment, therefore the decrease in renal function cannot be attributed only to the decrease in blood pressure, and the alternative and more probable explanation is the resolution of aldosterone-induced glomerular hyperfiltration after treatment(20)(21). Some studies have shown that the treatment of PA with mineralocorticoid receptor antagonists and surgery lowers GFR as volume expansion and glomerular hyperfiltration are mitigated (17)(22)(18). Thus, it seems clear that PA, regardless of the influences of blood pressure, is associated with a much higher risk of adverse renal outcomes compared to EH. Our hypothesis is that the higher risk of CKD in PA could be attributed to the effect of mineralocorticoid receptor activation by aldosterone in the context of volume expansion (23).
In our cohort of patients with PA, any clinical or hormonal characteristic was useful to predict CKD. However, the PAPY study found that plasma aldosterone, BMI, and age significantly predicted GFR (15). Wu et al. identified older age, diabetes mellitus, lower BMI, lower serum potassium, and higher PRA as factors related to kidney impairment in PA patients (24). Moreover, other authors demonstrated that pretreatment plasma aldosterone, plasma renin, plasma potassium, and pretreatment eGFR are independent predicting factors for the decline in GFR (18)(19); and others (21) that urinary albumin excretion and potassium were the only two independent predictors. The fact that any risk factor of GFR declination has been identified in our study could be justified by the matched process that eliminates differences in some known factors that affect kidney function and the similar cardiometabolic profile of both patient groups.
Another important finding was the significantly increased levels of PTH in patients with PA than in EH controls. The most plausible explanation in our study for this hyperparathyroidism is a secondary cause due to the higher prevalence of CKD in our cohort of PA. This theory is supported by other authors (25)(26). However, other authors (27)(28) have reported an increase in PTH levels in PA patients regardless of kidney function and vitamin D status. The exact mechanism by which aldosterone stimulates PTH remains unknown. However, evidence exists that aldosterone may impact on mineral homeostasis by increasing renal and fecal loss of calcium and magnesium and in turn, this may stimulate the secretion of PTH (29). Nevertheless, we cannot rule out a bidirectional interaction between the two hormonal systems as other studies have previously suggested (30)(31). The authors found the presence of mineralocorticoid and angiotensin II type 1 receptors in adenomatous tissue of the parathyroid gland, which could lead that both aldosterone and angiotensin II increased PTH secretion.
Although, globally, we could not demonstrate differences in the risk of cardiovascular disease between PA patients and controls, ischemic heart disease was six times significantly more common in PA patients than in EH controls. This is in agreement with the reported previously by several authors (3)(6)(32). Milliez et al. (3), were the first to demonstrate a significantly higher rate of myocardial infarction (4.0% vs 0.6%, P < 0.005) in a large cohort of patients with PA in comparison with EH patients matched by age, gender, BP, smoking history, creatinine and serum glucose levels. The French cohort of Savard et al. (6) also showed that patients with PA had a two-fold and 2.6-fold higher prevalence of coronary artery disease and nonfatal myocardial infarction, respectively. Moreover, a recent meta-analysis (33) including 3838 patients with PA and 9284 patients with EH with comparable baseline characteristics found that those patients with PA were at increased risk for coronary artery disease (OR 1.77, 95% CI = 1.10–2.83) compared with controls. Nevertheless, other authors (8–10) found no differences in the risk of ischemic heart disease. This discrepancy may be due to the lower incidence of coronary arterial disease in the Japanese population compared with Western countries. Racial differences and/or small number of events might explain the lack of significant difference in the analysis of ischemic heart disease risk (10). Likewise, in the work by Takeda et al. (8) EH controls were matched for age and gender but not for BP level.
During follow-up, our cohort of PA patients experienced a higher risk of deterioration of kidney function than controls, despite similar levels of SBP and DBP. Similar results were previously reported (24). There is limited information about the effect of prolonged aldosterone excess on kidney function (34); however, significant histological damage of the kidney has been noted in PA patients (35). There is evidence which supports that increased aldosterone is an independent contributor to small- and note-sized arterial injury and nephropathy (35), and that aldosterone-induced structural damage may affect primarily intrarenal vessels as a result of chronic hypertensive injury and aldosterone-related endothelial dysfunction (35)(19)(36). Furthermore, the glomerular hyperfiltration in PA plays a role in the progression of CKD (24), and the excessive urinary albumin excretion could be an indicator of target-organ damage associated with PA (37). Moreover, PA without suppression of plasma renin was associated with the histological evidence of renal arteriolosclerosis (38), and higher pretreatment renin concentrations were associated with a lower probability of curing hypertension and less improvement of albuminuria after treatment of PA (19). Therefore, an evolutionary pattern of kidney impairment in PA from initial functional adaptation to irreversible structural damage has been proposed (24).
As limitations of our study, it should be mentioned that it is a retrospective study, so no conclusions can be drawn in terms of causality. However, the presence of the matching process by age, sex, and degree of BP control limits the possibility of confusing factors and provides greater robustness to the results. Nevertheless, the fact that patients with PA needed more antihypertensive drugs than controls at diagnosis could introduce a bias as it could be related with a more severe hypertension and/or of longer duration. One strength of the study is a relatively large number of patients were included in the study. Another possible limitation of this study, it could be that patients with non-functioning incidentalomas were selected as controls, classified as such with classical hormonal studies, but that it cannot be ruled out that there is a secretion of other steroid hormones that could increase the cardiometabolic risk of these patients and reduce differences in the cardiometabolic profile between PA and EH patients (39)(40)(41).