What is the significance of elevated plasma aldosterone concentration (PAC) and low plasma renin activity (PRA) in the context of a benign adrenal myolipoma?

Assessment of Elevated Aldosterone-to-Renin Ratio with Adrenal Myolipoma

The laboratory findings suggest primary aldosteronism that is likely unrelated to the benign adrenal myolipoma, as the aldosterone-to-renin ratio is borderline elevated but does not meet definitive diagnostic criteria for primary aldosteronism. 1, 2

Interpretation of Laboratory Values

• Baseline PAC of 13.6 ng/dL with PRA of 0.7 ng/mL/h yields an aldosterone-to-renin ratio (ARR) of approximately 19.4, which is below the typical cutoff of 30 for primary aldosteronism diagnosis 1, 2
• Post-sodium loading test values show PAC increased to 17.3 ng/dL with PRA of 1.1 ng/mL/h, yielding an ARR of approximately 15.7 1
• The lack of aldosterone suppression with sodium loading is concerning, as aldosterone should normally decrease with sodium loading 2, 3
• The mild hypokalemia (K+ 3.4) at baseline that improved with salt loading (K+ 3.9) is atypical for primary aldosteronism, where salt loading typically worsens hypokalemia 1

Significance of Adrenal Myolipoma

• The 1 cm fatty lesion described as a benign myolipoma on the right adrenal gland is unlikely to be the source of aldosterone excess 1
• Myolipomas are typically non-functional adrenal tumors and rarely associated with hormone production 1
• Primary aldosteronism is usually caused by either an aldosterone-producing adenoma or bilateral adrenal hyperplasia, not myolipomas 1
• The CT finding of a stable myolipoma is likely an incidental finding rather than the cause of the laboratory abnormalities 2

Diagnostic Considerations

• The ARR is below the typical threshold of 30, but the plasma aldosterone concentration is above 10 ng/dL, which meets part of the criteria for a positive screening test 1, 2
• The lack of appropriate aldosterone suppression with salt loading suggests autonomous aldosterone production 2, 3
• However, the ARR decreased rather than increased with salt loading, which is atypical for primary aldosteronism 2
• The improvement in potassium with salt loading is also inconsistent with typical primary aldosteronism 1

Next Steps in Evaluation

• Additional confirmatory testing is warranted, such as the intravenous saline suppression test, to definitively rule in or out primary aldosteronism 1, 3
• If primary aldosteronism is confirmed, adrenal venous sampling would be recommended to determine if the source is unilateral or bilateral, as CT imaging alone is not reliable for subtype differentiation 2, 4
• The adrenal myolipoma should be monitored but is unlikely to require intervention based on its benign nature and stability on imaging 1

Management Implications

• If primary aldosteronism is confirmed and determined to be bilateral (idiopathic hyperaldosteronism), medical management with mineralocorticoid receptor antagonists (spironolactone or eplerenone) would be recommended 1, 2
• If unilateral disease is confirmed and located in the contralateral adrenal gland from the myolipoma, laparoscopic adrenalectomy could be considered 1
• Close monitoring of blood pressure and potassium levels is essential regardless of the final diagnosis 1, 5

Common Pitfalls to Avoid

• Relying solely on the ARR without confirmatory testing can lead to false positives or negatives 2, 6
• Assuming that any adrenal lesion is the cause of hormonal abnormalities without proper functional assessment 1, 4
• Failing to consider medication effects on the ARR interpretation (though not applicable in this case) 2, 3
• Not recognizing that hypokalemia is absent in the majority of primary aldosteronism cases and has a low negative predictive value 1, 5