Differential Diagnosis for Hypercalciuria and Elevated iPTH with Normal Serum Calcium
Single Most Likely Diagnosis
- Primary Hyperparathyroidism (PHPT) with normocalcemic variant: This condition is characterized by elevated parathyroid hormone (iPTH) levels with normal serum calcium levels. The normocalcemic variant of PHPT can present with hypercalciuria, and it is essential to consider this diagnosis, especially given the elevated iPTH levels.
Other Likely Diagnoses
- Familial Hypocalciuric Hypercalcemia (FHH): Although serum calcium is normal in this case, FHH can sometimes present with normocalcemia, especially in early stages or in mild forms. The presence of hypercalciuria and elevated iPTH warrants consideration of this diagnosis.
- Vitamin D Receptor Mutations: Mutations in the vitamin D receptor can lead to resistance to vitamin D action, resulting in elevated iPTH and hypercalciuria, despite normal serum calcium and vitamin D levels.
- Renal Tubular Acidosis: Certain types of renal tubular acidosis can present with hypercalciuria and elevated iPTH, even with normal serum calcium levels.
Do Not Miss Diagnoses
- Lithium-Induced Hyperparathyroidism: Lithium therapy can cause hyperparathyroidism, leading to elevated iPTH and hypercalciuria. It is crucial to inquire about lithium use in the patient's medication history.
- Malignancy-Associated Hypercalcemia: Although serum calcium is normal, certain malignancies can produce parathyroid hormone-related protein (PTHrP), leading to elevated iPTH levels and hypercalciuria.
- Multiple Endocrine Neoplasia (MEN) Syndromes: These syndromes can include primary hyperparathyroidism as a component and may present with normocalcemic hyperparathyroidism.
Rare Diagnoses
- Neonatal Severe Primary Hyperparathyroidism: This is an extremely rare condition, usually diagnosed in infancy, but it could potentially present later in life with atypical features.
- Jansen's Metaphyseal Chondrodysplasia: A rare genetic disorder characterized by abnormal bone growth and hyperparathyroidism, which could potentially present with normocalcemic hyperparathyroidism and hypercalciuria.