How should I manage an elderly woman with persistent hypernatremia, hypokalemia, stable renal function, and resistant hypertension despite increased lisinopril, and what is the likely cause?

Likely Cause: Primary Aldosteronism

This elderly woman most likely has primary aldosteronism causing her resistant hypertension with persistent hypernatremia (Na >145), hypokalemia (K <3.5), and inadequate blood pressure control despite escalating lisinopril. 1

Clinical Reasoning

The constellation of findings is highly suggestive of mineralocorticoid excess:

• Resistant hypertension (elevated BP despite increased ACE inhibitor)
• Hypokalemia (K <3.5) with likely inappropriate urinary potassium loss
• Hypernatremia (Na >145) reflecting sodium retention and volume expansion
• Stable renal function (making renal parenchymal disease less likely as primary cause)

Primary aldosteronism is found in 13% of patients with severe hypertension and is the most common secondary cause in resistant hypertension 2. The 2020 ISH guidelines specifically recommend screening for secondary causes in patients with resistant hypertension 1.

Immediate Diagnostic Workup

Screen for primary aldosteronism first:

1. Measure aldosterone-to-renin ratio (ARR) - ideally while patient is still on lisinopril, as ACE inhibitors can cause false negatives but screening should not be delayed 3
2. Check 24-hour urinary potassium - will be inappropriately elevated (>30 mmol/day) despite hypokalemia
3. Measure plasma aldosterone concentration (PAC) and plasma renin activity
4. Basic metabolic panel - document severity of electrolyte abnormalities
5. Adrenal CT imaging - look for adrenal adenomas once biochemical diagnosis is established

Important caveat: The ARR may be misleadingly low if measured while on lisinopril, but an elevated aldosterone with suppressed renin in the setting of hypokalemia is highly suggestive 3. Don't let a borderline ARR dissuade you from pursuing this diagnosis.

Management Algorithm

Step 1: Optimize Current Regimen While Investigating

Stop increasing lisinopril - ACE inhibitors can worsen hyperkalemia risk once mineralocorticoid antagonist is added 4

Add a thiazide-like diuretic (chlorthalidone 12.5-25 mg daily) to the current regimen:

• Addresses volume-mediated component of resistant hypertension 1
• More effective than hydrochlorothiazide for resistant hypertension 1
• However, will worsen hypokalemia - requires aggressive potassium supplementation

Aggressively replace potassium:

• Target serum K >4.0 mmol/L before adding spironolactone
• Use potassium chloride 40-80 mEq daily in divided doses
• Monitor closely as requirements may be substantial

Step 2: Add Mineralocorticoid Receptor Antagonist

Once K >4.0 mmol/L and eGFR confirmed >45 mL/min/1.73m², add spironolactone 25 mg daily 1

This is the fourth-line agent specifically recommended for resistant hypertension by 2020 ISH guidelines, particularly appropriate given the biochemical picture suggesting aldosterone excess.

Monitor within 1 week:

• Serum potassium (risk of hyperkalemia with ACE inhibitor + spironolactone combination) 4
• Serum sodium (should begin to normalize)
• Blood pressure
• Renal function

Step 3: Definitive Diagnosis and Treatment

If biochemical screening confirms primary aldosteronism:

1. Adrenal venous sampling (AVS) - essential to determine if unilateral (surgically curable) vs bilateral disease 1, 3

   • Should be performed at specialized center
   • Determines lateralization of aldosterone hypersecretion

2. If unilateral adenoma confirmed:

   • Laparoscopic adrenalectomy is curative 5, 3
   • Achieves normotension without medications in many cases
   • Corrects electrolyte abnormalities permanently

3. If bilateral disease:

   • Continue medical management with spironolactone (may need 50-100 mg daily)
   • Consider eplerenone if spironolactone side effects (gynecomastia, menstrual irregularities)

Critical Pitfalls to Avoid

Don't assume this is simply "difficult to control" essential hypertension - the electrolyte abnormalities demand investigation for secondary causes 1

Don't delay screening because patient is elderly - primary aldosteronism occurs across all age groups and is eminently treatable 5, 3

Don't attribute hypernatremia solely to age-related decreased thirst 6, 7 - while elderly patients have blunted thirst mechanisms, the combination with hypokalemia and resistant hypertension points to a specific pathophysiologic process

Don't overlook coexisting secondary causes - renovascular disease can coexist with primary aldosteronism 8, 5, 9. If BP remains uncontrolled after addressing aldosterone excess, consider renal artery stenosis imaging

Don't combine ACE inhibitor with ARB - this combination is explicitly not recommended and increases risk of hyperkalemia and renal dysfunction 4

Alternative Considerations

If primary aldosteronism is excluded, consider:

• Renovascular hypertension (renal artery stenosis) - particularly if abrupt worsening of previously controlled hypertension 8
• Medication nonadherence - confirm with pill counts or pharmacy records 1
• Excessive dietary sodium - 24-hour urinary sodium >150 mmol suggests poor dietary compliance 2, 10
• Volume overload - despite "stable" creatinine, subtle volume expansion drives resistant hypertension 10, 11

Expected Outcomes

With appropriate treatment:

• Blood pressure should improve within 4-12 weeks of adding spironolactone
• Potassium should normalize within days to weeks
• Sodium should gradually normalize as volume status improves
• If surgically treated adenoma: potential cure with medication discontinuation 5, 3

Refer to hypertension specialist if diagnosis remains unclear or BP uncontrolled after 3 months of optimized 4-drug therapy including mineralocorticoid antagonist 1