Case Presentation: A 55 year-old male with no known medical history presented to the emergency department after a fall on both knees. He was found to have bilateral patellar tendon ruptures and multiple femoral lytic bone lesions on radiographic imaging. Subsequent laboratory testing yielded an elevated creatinine (3.42 mg/dL) and hypercalcemia (15.2 mg/dL), concerning for multiple myeloma.
Aside from superior displacement of bilateral patellae, the physical exam was benign.
Further radiographs demonstrated lytic bone lesions of the ribs, clavicles and femurs. A CT did not show lymphadenopathy or organ involvement. Significant laboratory findings included a decreased vitamin D level (15 ng/mL), elevated alkaline phosphatase (738 U/L), an unremarkable serum protein electrophoresis and normal protein gap. Parathyroid hormone was elevated at 1801 pg/mL and an ultrasound revealed a 3 cm left-sided paratracheal mass consistent with a parathyroid tumor.
The patient underwent parathyroidectomy and pathology demonstrated benign parathyroid tissue consistent with a parathyroid adenoma. A biopsy of the femur lesion showed marrow fibrosis with morphologic changes suggestive of a brown tumor.
Discussion: Osteitis fibrosis cystica describes the fibrotic and cystic transformation of bones in primary hyperparathyroidism (PHPT). This end-stage skeletal manifestation of classic PHPT is now exceedingly rare with routine calcium screening. It was originally described in 1891 and is characterized by generalized bone demineralization, subperiosteal resorption, bone cysts and osteoclastomas or “brown tumors” based on their brownish color. Bony lesions are painful and pathologic fractures are common, however, changes are reversible with correction of PHPT after approximately six months. Skull radiographs in PHPT are described as having a “salt and pepper” appearance compared to “punched-out” lesions seen in multiple myeloma. Additionally, subperiosteal bone resorption leads to a “tapering” appearance of distal phalanges and the bone cortex is extremely thin particularly in the distal radius. Although lesions in multiple myeloma and primary hyperparathyroidism can occur in all bones, areas of increased hematopoiesis such as the vertebrae and pelvis are more commonly affected in multiple myeloma, whereas the jaw, ribs and long bones are more susceptible to increased osteoclastic activity.
Conclusions: Despite its characteristics, osteitis fibrosa cystica is not malignant but is locally invasive. Tools for diagnosis include bone biopsy, serum calcium and PTH. New advances in DEXA imaging (trabecular bone score) and high-resolution computed peripheral quantitative tomography (HR-pQCT) may provide a noninvasive method of classifying microstructural features in these patients.