Differential Diagnosis

The patient's serum aldosterone level is elevated at 26, with a plasma renin activity of 1.7 and an aldosterone-to-renin ratio (ARR) of 15.29. Notably, the patient does not have low potassium levels or hypertension (BP > 140/90 mmHg). Based on these findings, the differential diagnosis can be categorized as follows:

• Single Most Likely Diagnosis
  • Non-classic Congenital Adrenal Hyperplasia (CAH) or Familial Hyperaldosteronism Type I: The elevated aldosterone level and ARR suggest primary aldosteronism, but the absence of hypertension and hypokalemia is unusual. Non-classic CAH or Familial Hyperaldosteronism Type I could present with variable degrees of aldosterone elevation without the typical features of primary aldosteronism.
• Other Likely Diagnoses
  • Idiopathic Hyperaldosteronism: Although less likely due to the lack of hypertension, some cases of idiopathic hyperaldosteronism may not present with typical features.
  • Aldosterone-Producing Adrenal Nodule or Hyperplasia without Typical Primary Aldosteronism Symptoms: These conditions could lead to elevated aldosterone levels without causing significant hypertension or hypokalemia, possibly due to compensatory mechanisms or mild disease.
• Do Not Miss Diagnoses
  • Cushing's Syndrome: Although less likely given the specific pattern of hormone levels, Cushing's syndrome can sometimes present with elevated aldosterone levels. Missing this diagnosis could be critical due to its potential for severe morbidity.
  • Pheochromocytoma: Though typically associated with catecholamine excess, some cases might have co-secretion of aldosterone, making it a diagnosis not to be missed due to its potential for severe cardiovascular complications.
• Rare Diagnoses
  • Familial Hyperaldosteronism Types II, III, and IV: These are rare genetic conditions leading to excessive aldosterone production. They might not always present with the classic symptoms of primary aldosteronism.
  • Glucocorticoid-Remediable Aldosteronism (Familial Hyperaldosteronism Type I): A rare form of hyperaldosteronism that is responsive to glucocorticoid treatment, which could be considered in the differential diagnosis given the atypical presentation.

Each of these diagnoses requires careful consideration of the clinical presentation, laboratory findings, and potentially further diagnostic testing to determine the underlying cause of the patient's elevated aldosterone level and ARR.