(4.06) Atypical Presentation of Idiopathic Hypoparathyroidism in Adult Patient

A 66-year-old male, with no prior history of hypocalcemia, chronic kidney disease, or parathyroid surgery, experienced recurrent nephrolithiasis necessitating lithotripsy. Metabolic stone evaluation revealed hypercalciuria of 641 mg/day with a stone composition of calcium oxalate and calcium phosphate. Surprisingly, he exhibited low PTH levels at < 2 pg/mL (18-80), alongside corrected calcium at 9.9 mg/dL (8.3-10.6) and vitamin D 25-hydroxy at 34 ng/mL (≥20).

A comprehensive biochemical work-up was conducted, revealing consistent findings. Repeat PTH levels remained below 10 ng/mL (18-80), while calcium levels were within the normocalcemic range at 8.7 mg/dL (8.3-10.6). Ionized calcium measured 4.6 mg/dL (4.5-5.3), magnesium was within the normal range at 1.8 mg/dL (1.6-2.6), and phosphorus registered at 3 mg/dL (2.4-5.1). Vitamin D 25-hydroxy measured 30 ng/mL, and vitamin D 1,25-dihydroxy recorded 50 pg/mL, both falling within their respective reference ranges (≥20 and 18-64, respectively).

A chest X-ray and angiotensin-converting enzyme levels < 5 U/L (16-85) showed no signs of granulomatous disease. A DXA bone density scan revealed normal bone mineral density, and a thyroid soft tissue neck ultrasound displayed a normal thyroid gland without sonographic evidence of parathyroid glands.

Genetic testing for mutations in the calcium-sensing receptor (CaSR) was undertaken, but no reportable variants were detected. Subsequently, thiazide diuretics were initiated to address hypercalciuria, and the patient received dietary recommendations, including limiting sodium and protein intake while encouraging fluid consumption.

Discussion : The most common cause of hypoparathyroidism is associated with procedures, accounting for 70%. This case underscores the rarity of idiopathically low parathyroid hormone (PTH). Despite the low PTH levels, the rest of the biochemical workup remained within the reference range. Notably, he did not exhibit mucocutaneous candidiasis or adrenal insufficiency, the other two components of the classical triad of autoimmune polyendocrine syndrome type 1. Additionally, there were no physical features of Albright hereditary osteodystrophy. The absence of hypocalcemia, hyperphosphatemia, or hyperparathyroidism ruled out pseudohypoparathyroidism, and no variant was found in the CaSR gene. In the long term, thiazide diuretics effectively address asymptomatic hypercalciuria by enhancing renal calcium reabsorption and increasing serum calcium. If a patient were to develop symptoms, conventional therapies such as calcitriol and calcium supplementation can be administered.  Additionally, some studies have suggested treatment with PTH (1-34) as an alternative treatment to normalize 24-hour urine calcium.