This study presents a detailed assessment of the largest published PA series in a single center[19-21]. The gender ratio of PA patients showed that women took a more significant proportion than men, which is consistent with the results of previous studies, suggesting that the risk of PA among women is slightly higher than men[22]. In this study, the age of patients at the onset of PA is 30-59 years, and the most common age is 45-59 years, followed by 30-44 years, similar to that reported in other studies[22, 23]. Hypokalemia prevalence among patients diagnosed with PA was reported between 9–37%[3, 15, 16]. In our cohort, 26.9% of patients were diagnosed with hypokalemic PA variants, consistent with the above data. Therefore, hypokalemia is not a necessary condition for screening and diagnosis of PA, and the importance of hypokalemia as a suggestive clinical feature of PA has declined significantly.
Our study showed that women were more likely to have normokalemia in clinical characteristics. These results may be partly explained by the aldosterone antagonism secondary to progesterone. No significant difference was found in age between the two groups. However, the timing of the development of hypertension varies significantly, with higher long-term among patients with hypokalemic PA. This fact is relevant because recovery after adrenal resection is associated with a shorter time to hypertension evolution, as Celen et al.[24] reported. Therefore, a positive attitude seeking a specific diagnosis is crucial, especially in patients with hypokalemic PA.
It must be highlighted that the levels of mean systolic blood pressure, diastolic blood pressure and PAC were higher in patients with hypokalemic PA than in normokalemic PA, similarly to the published Spain cohort[25]. However, the median value of PAC was lower in our cohort than that in the reported European study of normokalemic PA[21]. In addition, ARR values were significantly higher in patients with hypokalemic PA than with normokalemic PA, which was inconsistent with the Spanish research that there was no significant difference in ARR between groups[25]. The reason for these conflicting results may be the differences in sample size.
A growing body of information from longitudinal and retrospective studies convincingly supports that PA patients had a higher incidence of complications in cerebrovascular events, coronary heart disease, arrhythmia, kidney damage, metabolic syndrome and diabetes compared with essential hypertension[4, 9-12, 18, 19, 21]. Millie et al. reported that the incidence of stroke (12.9% vs. 3.4%), myocardial infarction (4.0% vs. 0.6%) and atrial fibrillation (7.3% vs. 0.6%) in patients with aldosterone-induced adenoma and bilateral adrenal hyperplasia was significantly higher than that in patients with essential hypertension[19]. In addition, in the study by Born-Frontsberg et al., the incidence for cerebrovascular disease, including cerebrovascular stenosis, transient ischemic attacks (TIA), Prolonged Reversible Ischemic Neurological Defect (PRIND) and stroke, was 12.8% in PA. The incidence of cerebrovascular complications did not differ between the hypokalemic PA and normokalemic PA[21]. In our study, the incidence of cerebrovascular events, including cerebral infarction and cerebral hemorrhage, was 12.5%. There was no difference in cerebral infarction and cerebral hemorrhage prevalence between hypokalemic and normokalemic PA patients. The high occurrence of cerebrovascular events among PA patients may be explained by the elevated aldosterone concentrations independently from the blood pressure[26].
Elevated aldosterone concentrations harm endothelial dysfunction, independent of blood pressure, and are associated with microvascular inflammation and brain and heart muscle[27, 28]. Studies have reported that cardiovascular complications in patients with PA were higher than those with essential hypertension[4, 29]. In a French cohort, patients with PA had a significantly higher prevalence of coronary artery diseases (OR, 1.9), nonfatal myocardial infarction (OR, 2.6), heart failure (OR, 2.9) and atrial fibrillation (OR, 5.0) than properly matched controls with essential hypertension. However, cardiovascular complications were not significantly increased in PA patients with hypokalemia.[9] Catena et al.[30] also showed that cardiovascular complications were higher in PA than in essential hypertension (35% vs. 11%). The ORs of sustained coronary heart disease, cerebrovascular events and arrhythmias were higher at 2.80, 4.36 and 4.93, respectively. In addition, the study by Born-Frontsberg et al. [21] demonstrated a significant difference in the prevalence of cardiovascular comorbidities between hypokalemic and normokalemic PA (35.2% vs. 20.6%). The predominance of angina pectoris and chronic cardiac dysfunction was notably higher in the hypokalemic variant of PA than in the normokalemic variant. However, no significant difference in atrial arrhythmia was found between the two groups. Inconsistent with these findings, in the present study, the rate of cardiovascular comorbidities, including coronary heart disease and arrhythmia, was 16.7%, which was lower than that in the previous studies[21, 30]. There was no difference in atrial arrhythmia and coronary heart disease between patients with hypokalemic PA and hypokalemic PA. However, patients with hypokalemic PA showed trend toward higher prevalences of atrial arrhythmia, which may be accounted by low serum potassium level. Another reason for this result may be high aldosterone level in patients with hypokalemic PA. Elevated aldosterone concentration may be a risk factor for arrhythmias through left ventricular hypertrophy or primarily through left atrial fibrosis or a combination of both.[19] The possible reason for these conflicting results between different studies may be the differences in sample size. Therefore, further investigations with larger sample size are needed to confirm our findings.
Clinical studies have shown that PA is associated with renal complications, reflecting the ability of elevated aldosterone levels to cause renal dysfunction. In a large multicenter cross-sectional PAPY study, 24-hour microalbuminuria was significantly higher in patients with aldosterone adenoma and bilateral adrenal hyperplasia than in controls with essential hypertension[18]. Ribstein et al. found that PA was associated with relatively high filtration, and urine albumin excretion was significantly reduced in 25 patients with adrenal adenoma after adrenal resection for six months[31]. In a long-term study, Sechi et al. showed that the patients with PA had higher albuminuria than those controls with essential hypertension. Microalbuminuria was more likely to fall back to normal levels after treatment rather than progress to dominant albuminuria at a mean follow-up of 6.4 years[14]. Urinary microprotein is an early manifestation of renal damage, which appears before the increase of creatinine, urea nitrogen and the decrease of glomerular filtration rate, and can be used for early assessment of renal damage caused by PA. Our study found that the level of urinary microalbumin were higher in patients with hypokalemic PA than in patients with normokalemic PA. The number of renal insufficiency tended to be higher in patients with the hypokalemic PA, but there was no statistical difference between the two groups. These results suggest that hypokalemia may be an early indicator of renal damage in patient with primary aldosteronism.
Previous researches found that plasma and urinary aldosterone levels were significantly related to apnea-hypopnea index (AHI) in patients with resistant hypertension[32]. Two clinical observational studies showed that the AHI was significant reduction after two months of spironolactone treatment in patients with resistant hypertension and moderate-to-severe OSA[33]; and three months of eplerenone treatment patients with essential resistant hypertension and OSA, respectively[34]. Similarly, a small randomized, blank-controlled prospective trial showed significant reductions in OSA severity, blood pressure, and aldosterone levels in RH and moderate-to-severe OSA patients treated with spironolone for 3 months in addition to existing antihypertensive therapy compared to controls [35]. AHI and neck circumference were significantly reduced in patients with both PA and OSA after PA medical or surgical treatment [36]. Our study found a high prevalence of OSA in patients with PA. Meanwhile, OSA was higher in patients with hypokalemic PA than in those with normokalemic PA. These findings may be explained by that excessive aldosterone contributes to OSA. Aldosterone excess may be may be associated with the pathogenesis of airway obstruction, not only through fluid overload-mediated mechanisms, but also through direct injury and the disorders of central ventilator-control [37, 38].
There were some limitations in the present study. Firstly, this was a retrospective study at a single center. Futhurmore, our study had inherent limitations of these studies, including missing data. However, clinical care and structured data collection computerization led to < 15%. At the end, the machanism of the influnence of different serum potassium levels on PA comorbidities was not investigated in this study.