Pseudohypoparathyroidism versus signaling disorder: A case report

Pseudohypoparathyroidism is a terminology used to describe a group of metabolic disorders characterized by parathyroid hormone resistance. Patients with pseudohypoparathyroidism have hypocalcemia, hyperphosphatemia, and elevated serum parathyroid hormone. This methylation defect leads to signaling abnormalities in the parathyroid hormone and parathyroid hormone-related peptide receptor. We present a 40-year-old African American male who was referred to our endocrinology clinic for hypocalcemia. On physical examination, his body mass index was 34.3 kg/m² and he was found to have a round face, and several subcutaneous nodules on his scalp, hands, and legs. Laboratory findings revealed hypocalcemia, hyperphosphatemia, and elevated levels of intact parathyroid hormone and thyroid stimulating hormone (TSH). His hand X-ray showed brachydactyly of all metacarpal bones, and soft tissue calcifications. Brain CT indicated dense calcifications in the subcortical region, bilateral basal ganglia, bilateral thalami, bilateral cerebellum and vermis, and soft tissue calcifications in the scalp. The "inactivating parathyroid hormone/parathyroid hormone-related peptide signaling disorder" diagnostic approach suggested by the Euro pseudohypoparathyroidism network was applied to the patient, who was diagnosed with parathyroid hormone signaling disorder. Compared to the old pseudohypoparathyroidism classification and the 2018 Pseudohypoparathyroidism International Consensus Statement Report, the inactivating parathyroid hormone/parathyroid hormone-related peptide signaling disorder cluster classification appears to be more flexible, and easier to use. It also accommodates future inclusion of genetic mutations associated with hormonal signaling disorders. Adoption of the inactivating parathyroid hormone/parathyroid hormone-related peptide signaling disorder classification remains limited, and further larger studies are needed to compare the three approaches.