A Case of Osteitis Fibrosa Cystica of the Mandible: A Rare Presentation during Pregnancy due to Mutation.

Typically, primary hyperparathyroidism (PHPT) develops as a result of multiglandular hyperplasia, parathyroid cancer, or parathyroid adenoma. Patients usually present with skeletal manifestations such as low-trauma fractures. Osteitis fibrosa cystica (OFC) is a classic yet rare skeletal manifestation of advanced PHPT currently reported in less than 2% of patients. We present a case of a 29-year-old Indian female who presented with a femur fracture and mandibular OFC 20 days after delivery. The painless mandibular swelling gradually progressed from the third month of pregnancy. The biochemical and radiological investigations were indicative of PHPT-associated OFC. After the excision of the three-and-a-half parathyroid gland, histology revealed benign cystic adenomas and hyperplasia. Based on the associated clinical manifestations, OFC was suspected. Clinical exome sequencing revealed (+) c.687_688dupAG heterogenous pathogenic autosomal dominant mutation. Undiagnosed PHPT in mothers during pregnancy led to neonatal hypocalcaemic convulsions. With adequate supplementation, the infant recovered completely from transient congenital hypoparathyroidism. OFC is an important diagnosis to consider in a young patient with swelling of the neck and jaw. Simultaneous high levels of PTH and serum calcium should raise a high index of suspicion for OFC. Parathyroidectomy helps manage the biochemical abnormalities and causes regression of the jaw mass that causes facial disfigurement and attenuates the declining BMD. Children born to mothers with PHPT should be evaluated for neonatal hypoparathyroidism and supplemented appropriately to reduce the risk of hypocalcaemic manifestations that can be life-threatening. If the mutation is detected, the offspring should be monitored for signs of PHPT due to the high probability of inheritance and parathyroid malignancy.