In an 84-year-old woman with borderline hypercalcemia, markedly elevated intact parathyroid hormone (PTH), and mildly impaired renal function (creatinine 1.24 mg/dL), what is the most likely diagnosis and how should it be evaluated and managed?

Primary Hyperparathyroidism (PHPT) is the Most Likely Diagnosis

This 84-year-old woman has primary hyperparathyroidism (PHPT), characterized by borderline elevated calcium (10.2 mg/dL) with markedly elevated PTH (264 pg/mL) and mild renal impairment. This presentation is typical for PHPT, which is particularly common in postmenopausal women and increases in prevalence with advancing age 1.

Diagnostic Confirmation Required

Before finalizing the diagnosis of PHPT, you must systematically exclude causes of secondary hyperparathyroidism:

Essential First Steps:

1. Measure 25(OH) vitamin D levels immediately - Vitamin D deficiency/insufficiency is a frequent cause of secondary hyperparathyroidism and must be corrected and maintained at normal levels for >6 months before accepting a diagnosis of PHPT 2

2. Calculate fractional excretion of calcium (FeCa) using the formula:

   • FeCa = (urinary calcium × plasma creatinine) / (urinary creatinine × plasma calcium)
   • FeCa >2% confirms PHPT and distinguishes it from familial hypocalciuric hypercalcemia (FHH)
   • This should be included in first-line investigations 2

3. Assess calcium intake - Insufficient dietary calcium can cause secondary hyperparathyroidism 2

4. Measure ionized calcium - Given the borderline total calcium, ionized calcium provides more definitive evidence of hypercalcemia 2

Mandatory Target-Organ Assessment

Since PHPT is asymptomatic in 80-90% of cases, you must systematically evaluate for complications 1, 2:

Renal Evaluation (Grade A++):

• Estimate GFR (already showing impairment with creatinine 1.24)
• 24-hour urine calcium and fasting calcium/creatinine ratio
• Non-contrast low-dose CT scan of kidneys/urinary tract - more sensitive than ultrasound for detecting asymptomatic stones or nephrocalcinosis 1
• Nephrology referral indicated given GFR <60 mL/min/1.73m² 1

Skeletal Evaluation (Grade A++):

• DEXA scan of spine, femur, AND radius (distal radius particularly affected in PHPT)
• Spine X-rays or vertebral fracture assessment to detect asymptomatic vertebral fractures 1

Management Algorithm

Surgical Indications:

Parathyroidectomy is the only curative treatment and should be considered based on:

• Age <50 years (not applicable here)
• Serum calcium >1 mg/dL above upper normal limit
• GFR <60 mL/min/1.73m²
• Presence of kidney stones or nephrocalcinosis
• Osteoporosis (T-score ≤-2.5) or fragility fractures
• Patient preference for surgery

Given her age (84 years), mild renal impairment, and borderline calcium, surgical candidacy depends on:

1. Presence of kidney stones/nephrocalcinosis on imaging
2. Bone density results
3. Surgical risk assessment
4. Patient preference

Medical Management:

If surgery is not indicated, contraindicated, or refused:

• Monitor calcium, PTH, creatinine every 6-12 months
• DEXA scan every 1-2 years
• Maintain adequate hydration (reduces stone risk)
• Avoid thiazide diuretics (worsen hypercalcemia)
• Consider calcimimetics (cinacalcet) to lower calcium and PTH if symptomatic hypercalcemia
• Consider bisphosphonates or denosumab if osteoporosis present (though no fracture data specific to PHPT) 3

Critical Pitfalls to Avoid

1. Do not diagnose PHPT without excluding vitamin D deficiency - This is the most common error; vitamin D must be normal for >6 months 2

2. Do not rely on total calcium alone - Measure ionized calcium and FeCa for diagnostic certainty 2

3. Do not skip target-organ assessment - Complications are frequently asymptomatic and directly impact management decisions 1, 2

4. Do not assume surgery is inappropriate due to age alone - Surgical outcomes in carefully selected elderly patients can be excellent; base decision on comorbidities and functional status 1

5. Consider parathyroid carcinoma if PTH >1000 pg/mL with severe hypercalcemia and large parathyroid mass 4 - though this patient's PTH of 264 makes this unlikely

Special Considerations in the Elderly

The 2025 French consensus specifically addresses elderly patients with PHPT 1. While surgery remains definitive treatment, conservative management is reasonable in patients >50 years with:

• Calcium <1 mg/dL above upper normal limit
• No evidence of skeletal or kidney disease
• Acceptable surgical risk

However, the presence of renal impairment (creatinine 1.24) in this patient warrants thorough evaluation before deciding on conservative management 1.