Primary hyperparathyroidism (PHPT) is characterized by excessive secretion of parathyroid hormone (PTH), leading to disruptions in calcium and phosphate homeostasis. It is typically more common in older adults but can manifest in younger individuals, occasionally resulting in severe skeletal complications such as osteitis fibrosa cystica (OFC). This case report highlights a rare presentation of advanced OFC in a 25-year-old male in Egypt, aiming to emphasize the need for increased awareness and early detection of PHPT in young adults.

A 25-year-old unmarried male presented to an orthopedic clinic with a six-month history of progressive right-hand swelling, debilitating bone pain, and decreased grip strength. His symptoms were accompanied by chronic constipation and episodes of epigastric pain. Physical examination revealed tenderness and mild swelling in the right hand, while laboratory tests indicated marked hypercalcemia (13.5 mg/dL), hypophosphatemia (2.0 mg/dL), elevated PTH (180 pg/mL), and significantly raised alkaline phosphatase (ALP: 1400 IU/L). Radiographic imaging displayed classic features of OFC, including subperiosteal erosions and acro-osteolysis. A neck ultrasound confirmed parathyroid hyperplasia.

The patient's laboratory findings aligned with a diagnosis of OFC secondary to PHPT. Following surgical evaluation, a parathyroidectomy was performed, resulting in significant clinical improvement and normalization of calcium and PTH levels postoperatively. At the six-month follow-up, the patient reported resolution of bone pain and regained functional ability, showcasing the effectiveness of early surgical intervention in PHPT.

This case underscores the critical importance of recognizing PHPT in young adults, particularly in regions with limited access to routine biochemical screening. While OFC is increasingly rare in high-income settings, it still presents a significant diagnostic challenge in resource-limited areas. Clinicians must maintain a high index of suspicion for PHPT in patients exhibiting unexplained osteolytic lesions and functional impairments. Early biochemical testing is essential for timely diagnosis and intervention, as parathyroidectomy can lead to complete resolution of symptoms and prevention of irreversible complications. Increased awareness and routine screening for calcium disorders are vital in improving outcomes for young patients with PHPT.