Endocrine Abstracts

JOINT3483

Introduction: Familial hypocalciuric hypercalcemia (FHH) is a rare benign hypercalcemia that is sometimes difficult to distinguish from moderate primary hyperparathyroidism (HPT1). Familial hypocalciuric hypercalcemia (FHH) is an autosomal dominantly inherited disorder of calcium metabolism. Its main feature is mild to moderate hypercalcemia, mostly persistent and non-progressive, hypocalciuria, with normal or slightly elevated serum PTH levels. It is typically found in otherwise healthy and asymptomatic individuals. The coexistence of familial hypocalciuric hypercalcemia (FHH) and primary hyperparathyroidism (PHPT) is extremely rare.

Case Report: We report the case of a 56-year-old female patient with hypercalcaemia associated with hyperparathyroidism. The corrected calcaemia was elevated to 109 mg/l (reference values [RV] 86-100) with a PTH 1-84 at 240 pg/ml (RV 9.20-44.6) and a low calciuria at 75 mg/24h (RV 100-320), associated with a scintigraphy showing a 12*9 mm parathyroid adenoma on the lower left parathyroid, the patient did not adhere to the criteria for surgery of a HPT1. Strict monitoring of blood calcium levels and urinary and bone clinical signs was indicated. The hypocalciuria was controlled two times, then a diagnosis of an association of a HHF and a HPT1 was suspected.

Discussion: The diagnostic usually includes family history, clinical assessment, laboratory studies, 24-hour urine calcium excretion measurement. Genetic testing for CASR mutations is recommended in ambiguous cases revealing a heterozygous mutation in exon 4 of the calcium sensor gene. In our case it was not yet tested. Treatment mainly involves patient education and reassurance, with calcimimetic medications like Cinacalcet-HCL used in more symptomatic cases, despite not being FDA-approved for FHH.

Conclusion: Diagnosing FHH can be challenging due to its overlap with primary hyperparathyroidism (PHPT). The association of the two pathologies is rare. The possibility of Marx syndrome was raised by the hypocalciuria.