Osteitis Fibrosa Cystica: An Unusual but Still Prevalent Manifestation of Uncontrolled Secondary Hyperparathyroidism

Background: Osteitis fibrosa cystica is an uncommon complication of untreated secondary hyperparathyroidism in patients with end-stage renal disease. The characteristic bony lesions that are seen in this condition very rarely can regress after medical treatment or parathyroidectomy. Clinical Case: A 65-year-old male with PMH of Systemic Lupus Erythematous (SLE) resulting in End-Stage Renal Disease (ESRD) on peritoneal dialysis (PD) and HTN, presented to his primary care physician for evaluation of a painful, enlarging lesion in his left forearm. The patient reported no history of trauma and denied having systemic symptoms. An X-Ray of his left forearm showed a lytic lesion within the proximal neck of the ulna, with erosion of the adjacent cortex. CT of the forearm showed a very vascular soft tissue mass causing significant erosive changes of the anterior cortex in the proximal ulna. Due to the characteristics of the lesion, an underlying malignancy was suspected as a possible diagnosis. The patient had a whole-body PET CT which showed multiple scattered hypermetabolic lytic osseous lesions throughout the axial and appendicular skeleton, including a large left proximal ulnar lesion. The patient had a bone biopsy from the lesion in his left ulna which showed a giant cell proliferation in a background of fibrosis and hemosiderin, suggestive of Osteitis Fibrosa Cystica (brown tumor of hyperparathyroidism). His laboratory workup around the time of the symptoms showed a normal serum calcium (9 mg/dl), associated with a high serum phosphorus (6.2 mg/dl), low vitamin D (20 ng/ml), and an elevated PTH (900 pg/ml). The patient was started on Cinacalcet, an increased dose of phosphate binders, as well as Calcitriol and the lesions and pain disappeared. Follow up lab work showed a normal Vitamin D (34 mg/dl), normal Phosphorus (4 mg/dl), and a PTH of 199 mg/dl, with a normal serum Calcium. A surveillance PET was performed 6 months after the initial one when the lesions clinically had disappeared and it showed again the presence of the bony lesions described prior, including the one in the left ulna, but with decreased FDG uptake, as well as new lesions in the spine. To date, the patient is asymptomatic and has not noted any new painful lesions. Conclusions: Osteitis fibrosa cystica remains a rare manifestation of secondary hyperparathyroidism, which may lead to an initial impression of malignancy. This patient exhibited clinical resolution of the painful symptoms associated with osteitis fibrosa cystica following medical management, though the lytic lesions involving the axial and appendicular skeleton persisted on surveillance imaging. This case serves as a reminder of the severe manifestations of a skeletal disease that has become rare given advances in early detection of and appropriate medical management of hyperparathyroidism.