Hypoparathyroidism

Our patient initially presented at the age of 20 with tetany and paresthesias. Her past medical history is significant for hypothyroidism and psoriasis. She has not had surgery or radiation to the head and neck. She has a sister with hyperthyroidism but no known family history of calcium abnormalities. Her only medication is levothyroxine. On the physical exam, she has positive Chvostek’s and Trousseau’s signs. On laboratory testing, she is found to have a calcium of 6.2 mg/dL (normal range 8.5–10.5 mg/dL) with albumin 4.0 mg/dL, magnesium 2.1 mg/dL, and phosphorus 6.7 mg/dL (normal range 2.5–5.0 mg/dL). Ionized calcium is 0.77 mmol/L (low) and PTH is low at 1 pg/mL. 25-hydroxyvitamin D was 24 ng/mL with reportedly normal levels of 1,25-hydroxyvitamin D (value not available). She was started on calcium carbonate 500 mg TID, calcitriol 0.25 mcg BID, as well as cholecalciferol. Hypocalcemia persisted even after repletion of vitamin D. She did not have features suggestive of the genetic syndromes which have a known association with hypoparathyroidism; thus a presumptive diagnosis of autoimmune hypoparathyroidism was made. She subsequently had testing of calcium-sensing receptor (CaSR) antibodies; however, the results were not clearly diagnostic of an activating mutation.