In a patient with high‑normal serum calcium, elevated 24‑hour urinary calcium, and nodular enlargement of all four parathyroid glands, does this represent normocalcemic primary hyperparathyroidism?

Yes, this patient has normocalcemic primary hyperparathyroidism (NPHPT)

A patient with high-normal serum calcium, elevated 24-hour urinary calcium, and nodular enlargement of all four parathyroid glands meets the diagnostic criteria for normocalcemic primary hyperparathyroidism, provided secondary causes have been excluded. 1, 2

Diagnostic Reasoning

The 2025 French Expert Consensus explicitly recognizes normocalcemic hyperparathyroidism as an atypical form of primary hyperparathyroidism, defined as "normal calcemia with increased PTH level, not secondary to another cause" 1. Your patient's presentation aligns with this definition, with the added anatomical confirmation of four-gland involvement.

Key Diagnostic Features Present:

• High-normal serum calcium: While not overtly hypercalcemic, high-normal calcium with elevated PTH is pathological 2
• Elevated 24-hour urinary calcium: This is typical of PHPT and helps distinguish it from familial hypocalciuric hypercalcemia 2
• Fractional excretion of calcium (FeCa) >2%: This should be calculated and strongly supports PHPT over other diagnoses 2
• Four-gland nodular enlargement: This anatomical finding provides direct evidence of parathyroid pathology

Critical Exclusions Required Before Diagnosis

Before accepting this diagnosis, you must rigorously exclude secondary causes 1, 2:

1. Vitamin D status: Maintain normal 25(OH)vitamin D levels for >6 months before diagnosing NPHPT 2
2. Calcium intake: Insufficient dietary calcium is an underrecognized cause of elevated PTH with normal calcium 2, 3
3. Renal function: Chronic kidney disease causes secondary hyperparathyroidism 1
4. Medications: Loop diuretics and other drugs can elevate PTH 3
5. Malabsorption: Bariatric surgery, chronic diarrhea, or other causes of reduced intestinal calcium absorption 2

Diagnostic Algorithm:

1. Confirm PTH elevation with simultaneous normal serum calcium on multiple measurements (not just one)
2. Measure ionized calcium to exclude subtle hypercalcemia 2
3. Calculate FeCa: (urinary Ca × plasma Cr)/(urinary Cr × plasma Ca) × 100; >2% indicates PHPT 2
4. Verify vitamin D sufficiency maintained for >6 months 2
5. Assess dietary calcium intake using validated questionnaire 2
6. Consider oral calcium loading test if diagnosis remains uncertain: failure to suppress PTH after calcium load confirms autonomous parathyroid function 2

Clinical Significance of Four-Gland Disease

The presence of nodules on all four parathyroid glands is particularly important because:

• NPHPT has a higher prevalence of multigland disease compared to hypercalcemic PHPT 4, 5
• This may represent parathyroid hyperplasia rather than adenoma
• Four-gland involvement suggests more advanced or aggressive disease
• This finding increases the likelihood of recurrence after surgery 4

Management Implications

NPHPT patients often have MORE substantial skeletal and renal involvement than typical hypercalcemic PHPT 6, 7. Studies show:

• 57% have osteoporosis at diagnosis 6
• 14% have history of kidney stones 6
• 40% develop further complications over time 6

Surgical Considerations:

Parathyroidectomy is appropriate for this patient given the anatomical confirmation of four-gland disease, but be aware:

• All four glands will likely require removal (subtotal parathyroidectomy or total parathyroidectomy with autotransplantation)
• Preoperative localization may be more challenging than in hypercalcemic disease 4
• Risk of persistent or recurrent disease is higher with multigland involvement 4, 8
• Post-operative improvements in bone mineral density are well-documented 4, 7

Common Pitfalls to Avoid

1. Don't diagnose NPHPT on a single set of labs: Requires persistent findings over time 1
2. Don't skip the calcium supplementation trial: 50% of "normocalcemic hyperparathyroidism" resolves with adequate calcium intake 3
3. Don't assume normal vitamin D means adequate: Must maintain sufficiency for >6 months 2
4. Don't expect typical imaging findings: Adenomas may be smaller and harder to localize 4
5. Don't underestimate disease burden: These patients often have MORE complications than hypercalcemic patients, likely due to longer disease duration before diagnosis 6, 7