Bone Scintigraphy and SPECT/CT in Bisphosphonate-Induced Osteonecrosis of the Jaw

TO THE EDITOR: Dore et al. have recently published an interesting study on the promising role of ^99mTc-methylene diphosphonate (MDP) hybrid SPECT/CT to support the diagnosis of clinically suspected osteonecrosis of the jaw in 15 neoplastic patients, 4 of whom were affected by multiple myeloma and treated with bisphosphonates (1). As the authors clearly demonstrated, increased focal uptake of the radiocompound in the osteolytic areas identified by CT scans was significantly associated with histologically proven osteonecrosis of the jaw.

In hematology, almost all cases of osteonecrosis of the jaw occur in patients affected by multiple myeloma after exposure to bisphosphonates with or without chemotherapy; in this context, the most frequent diagnostic question is whether a painful area with radiographic signs of osteolysis in the maxillary region, be it swollen or not, is caused by a neoplastic focus or by an inflammatory or necrotic process. In this setting, ^99mTc-MDP–based techniques of bone imaging are not helpful for the differential diagnosis. ^99mTc-MDP binds to hydroxyapatite crystals in sites of active osteoblastic activity, which is erratic in osteolyses caused by neoplastic plasma cells (2). The comparison between an imaging technique based on a compound taken up by neoplastic cells and not by inflammatory ones, such as sestamibi scintigraphy (3), and an imaging procedure exploiting a tracer taken up also by inflammation, such as ¹⁸F-FDG PET, has recently been shown to be helpful in differentiating osteonecrosis of the jaw from myeloma osteolysis (4). This differentiation is possible because sestamibi head SPECT does not show focal maxillary uptake in osteonecrosis of the jaw and ¹⁸F-FDG PET does, whereas both sestamibi and ¹⁸F-FDG are taken up by focal myeloma lesions. Thus, invasive and potentially harmful procedures to obtain histologic specimens could be avoided.

It should be worthwhile to investigate whether, in association with sestamibi head SPECT, ^99mTc-MDP SPECT/CT is as informative as ¹⁸F-FDG PET/CT in differentiating myeloma lesions from osteonecrosis of the jaw.