Recklinghausen–Engel syndrome and tumor-like skeletal lesions in hyperparathyroidism: literature review and clinical case

Aim of the study: to provide a contemporary overview of the nomenclature and terminology of Recklinghausen– Engel syndrome (parathyroid osteodystrophy), its pathogenesis, and characteristic morphological and radiological manifestations. Special attention is paid to the differential diagnosis between brown tumor and skeletal giant cell tumor. The study aims to present the clinical and morphological criteria for distinguishing these conditions, systematized in a comparative table. Material and Methods. A literature search was conducted in the Medline, PubMed, Elibrary, and other databases. Of the 100 identified publications, 30 were included in this systematic review. We report a case of a resected brown tumor of the femur in a 58-year-old man with previously undiagnosed hyperparathyroidism, detailing the morphological diagnostic features and the disease course. Results. Recklinghausen-Engel syndrome (parathyroid osteodystrophy) is a rare but clinically significant metabolic skeletal disorder that develops in the setting of hyperparathyroidism. It is characterized by marked osteoclastic activity, the formation of cystic lesions, subperiosteal resorption, and so-called brown tumors. Despite its benign nature, this syndrome often mimics aggressive giant cell bone tumors, which complicates the interpretation of clinical, radiological, and morphological data and increases the risk of diagnostic errors. Conclusion. This article discusses the diagnostic challenges in the absence of overt clinical symptoms of hyperparathyroidism and emphasizes the key role of the pathomorphologist within a multidisciplinary team. Timely detection of parathyroid hormone hypersecretion and radical removal of the hyperplastic or neoplastic parathyroid gland lead to the regression of bone lesions and a favorable prognosis.