Primary Lymphoma Arising in Paget's Disease in A Patient with Primary Hyperparathyroidism.

Background: Paget's disease of bone (PDB) is characterized by a disturbance of the balance between bone formation and bone resorption at one or more bone sites. Its neoplastic transformation to osteosarcoma of the bone has been widely cited in the literature; however, association with non-Hodgkin's lymphoma (NHL) is very uncommon. In addition, whereas the pathophysiological relationship between PDB and secondary hyperparathyroidism is well established, there is much debate about the association between PDB and primary hyperparathyroidism (PHPT). Case Report: We present a case of NHL arising in pagetoid bone in a 56-year-old man, who was subsequently diagnosed with primary hyperparathyroidism (PHPT). Discussion: The malignant potential of pagetoid bone is well known, with sarcomatous degeneration being the most common neoplasm. Therefore, when pain recurred in our patient, 3 years after treatment of PDB, the presumptive diagnosis was a sarcomatous degeneration of the pagetoid bone. However, bone biopsy revealed a primary lymphoma, an extremely rare association that has been described only in a few cases. In addition, PHPT is rarely associated with PDB, although a link between PHPT and an increased risk of malignancy has been suggested. Conclusion: To the best of our knowledge, this is the first case of these three different bone diseases in the same patient. Further studies are needed to understand the possible molecular basis of the association among these diseases. LEARNING POINTS: Sarcomatous degeneration is the most common primary bone neoplasm associated with Paget's disease of bone (PDB). However, primary lymphoma in pagetoid bone is unusual.The association between PDB and primary hyperparathyroidism is very rare.The uniqueness of this case lies in coexistence of three bone diseases in the same patient.