Category: Calcium/Bone Disorders
We report a rare case of hypocalcemia presumably due to defective endogenous 1,25 Vitamin D which had an excellent response to exogenous calcitriol.
Methods : N/A
Case: 37 years old female was referred to Endocrinology office for management of hypocalcemia. She had multiple episodes of carpopedal spasms with numbness and tingling over the past 12 years and was found to have severe hypocalcemia. She was initially started on calcium and vitamin D3 supplements but had recurrent symptoms and was subsequently started on calcitriol with improvement in symptoms. She had run out of her medications for a few months before being seen at our office and lab work showed critically low calcium at 6.8 mg/dl. Further workup revealed very high PTH of 387 pg/ml ruling out autoimmune hypoparathyroidism. Her renal functions were normal. Her phosphate, 25-hydroxyvitamin D (calcidiol, 44 ng/ml) and 1,25-dihydroxyvitamin D (calcitriol, 32 pg/ml) levels were also normal ruling out pseudohypoparathyroidism and Vitamin D deficiency. Her 24-hour urinary calcium was initially slightly elevated but normalized after she limited salt and processed food intake. It was felt that the patient has resistance to endogenous vitamin D 1,25 and she was subsequently placed on calcitriol 0.25 mcg daily along with calcium supplements. She had an excellent response with normalization of calcium levels, reduction in PTH levels and no recurrence of symptoms.
This patient does not fit into any categories of hypocalcemia previously described in literature. One possibility is that she may have defective endogenous hormone or deficient vitamin D receptors resulting in the lack of adequate response to her endogenous 1,25 Vitamin D. Another possibility is that she may have defective feedback mechanism and not generating enough biologically active 1,25 Vitamin D even in the presence of severe hypocalcemia and hyperparathyroidism both of which stimulate renal activation of Vitamin D. It is unclear why these symptoms appeared so late in life. It is also interesting and unclear that why she responded to exogenous calcitriol when she is resistant to her endogenous hormone, as both are structurally identical. No strong clinical data is available in this regard in adults as only one other case has been reported in literature with similar findings and response with calcitriol. Genetic analysis for above mentioned hypothesis may be helpful in further explaining this rare and new clinical entity.
Conclusion : Resistance to endogenous 1,25 Vitamin D should be considered when hypocalcemia occurs with hyperparathyroidism in the setting of normal Vitamin D and phosphate levels and normal renal functions.
Wellspan York Hospital
I am an internal medicine resident at York Hospital. I am planning to pursue Endocrinology fellowship. I like to travel and take pictures.
Internal Medicine Resident at York Hospital. I will be starting my Endocrinology fellowship at University of Maryland next year. I have a special interest in Thyroid disorders.