Hyponatremia
This elderly patient's presentation is best described as hyponatremia (Option A), which is the primary driver of his neuropsychiatric symptoms of agitation and irritability. 1, 2
Clinical Reasoning
The patient presents with a sodium of 121 mEq/L, which represents moderate hyponatremia (125-129 mEq/L range defines moderate, and <125 mEq/L defines severe). 1 His neuropsychiatric symptoms of agitation and irritability are classic manifestations of hyponatremia, which commonly presents with nausea, vomiting, weakness, headache, and mild neurocognitive deficits at this level. 1
Why Hyponatremia is the Answer
- Thiazide diuretics are the most common cause of severe community-acquired hyponatremia, accounting for 41% of cases in patients admitted with sodium ≤120 mEq/L. 2
- The American Geriatrics Society specifically warns that thiazide diuretics are associated with hypokalemia and require electrolyte monitoring within 1-2 weeks of initiation, with dose increases, and at least yearly. 3
- Elderly women on thiazides are particularly at risk for severe electrolyte disturbances. 2, 4
- Indapamide and other thiazides can cause severe hyponatremia with predominant CNS symptoms that drive the clinical presentation. 4
Why Not the Other Options
Hyperkalemia (Option B)
While the potassium is elevated at 5.9 mEq/L, this is not causing his symptoms. The American Geriatrics Society guidelines note that ACE inhibitors (lisinopril) combined with thiazides can cause hyperkalemia, particularly in elderly patients with diabetes. 3 However, hyperkalemia at this level (5.9 mEq/L) typically does not cause agitation or irritability—it causes cardiac arrhythmias and muscle weakness when severe. 3 The hyperkalemia here is likely secondary to the ACE inhibitor in the setting of renal dysfunction from volume depletion. 3
Hypercalcemia (Option C)
The calcium of 2.8 mmol/L (assuming this is ionized calcium, which would be elevated, or ~11.2 mg/dL if total calcium) could represent hypercalcemia. However, this must be corrected for the severely low albumin of 1.8 g/dL. 3 The corrected calcium would likely be normal or only mildly elevated, making this an unlikely primary cause of his acute neuropsychiatric symptoms.
Hypoalbuminemia (Option D)
While the albumin of 1.8 g/dL is indeed low, hypoalbuminemia does not cause acute agitation and irritability. 3 It reflects chronic nutritional status or liver disease but is not the acute problem driving his presentation.
Critical Management Points
Immediate monitoring is essential because inappropriately rapid correction of sodium (>12 mmol/L in first 24 hours) occurs in 15% of cases and can cause osmotic demyelination syndrome, particularly in elderly patients who abuse alcohol or have hypokalemia. 2
The thiazide diuretic must be discontinued immediately, and the American Geriatrics Society recommends that patients on thiazides should have electrolytes monitored to prevent exactly this scenario. 3, 5
The hyperkalemia requires concurrent attention: ACE inhibitors should be monitored closely in elderly patients, with renal function and potassium checked within 1-2 weeks of initiation and at least yearly. 3 In this case, the lisinopril may need to be held temporarily given the hyperkalemia and likely volume depletion. 3