Plain films of the ribs (95k bytes) and left femur (41k bytes) were obtained for comparison at the time of the nuclear medicine study and revealed a diffuse lytic process involving essentially all of the visible bones. The mild increased activity in the left femur (arrow, 63k bytes) on bone scintigraphy activity was noted to correspond to periosteal reaction (arrow, 41k bytes) at a site of pathologic fracture. All of the above imaging findings were consistent with the diagnosis of multiple myeloma.
Bone scan mechanism of uptake is directly related to blood flow and degree of osteoblastic activity. Autoradiographic studies have shown the deposition of radiolabeled phosphates at sites of osteoid mineralization with Tc-99m labeled bone tracers exchanging with ions in the actively forming hydroxyapatite complex. Bony metastatic disease results in carcinomatous osteodysplasia which refers to a histologic alteration resulting in a variable increase in osteoblasts, osteoclasts, blood vessels, and other stromal tissues. More often than not this will result in increased activity on a bone scan. Over 80% of bony metastases originate from breast, prostate, lung and, much less frequently, thyroid and kidney. The osteoblastic response is less likely with the round cell group of tumors (lymphomas, leukemias, myeloma) and with highly vascular or anaplastic tumors (thyroid and kidney often placed in this category). The round cell group of tumors have been shown to produce osteoclast-activating and osteoblast-inhibiting factors. The highly vascular or anaplastic tumors are associated with very little osteoblastic activity. However, thyroid and renal cell cancer often present with solitary metatases, rapid progression and associated soft tissue masses. Although scintigraphy may be false negative, these tend not to be clinically occult lesions. In addition, one study demonstrated that 42% of radiographically occult renal cell metastases were scintigraphically positive (Cole). Renal cell cancer also has been shown to not uncommonly present as a cortical metastasis, usually scintigraphically positive (Hendrix).
Multiple myeloma is the most common primary bone tumor. It is of plasma cell origin, most commonly presents in the 40-70 year age group, female more frequently than male. The radiographic findings are characterized by round, punched out, clean cut areas of destruction with no surrounding sclerosis. However, radiographs may be normal or show only diffuse osteopenia. The sensitivity of radiography versus bone scanning for detecting multiple myeloma has been reported from 75-91% for radiography and 46-60% for scintigraphy (Ludwig, Woolfenden). A Mayo Clinic study (Whaner) concluded that, for multiple myeloma, scintigraphy
A recent case report of the successful palliation of painful multiple myeloma lesions with Sr-89 raises a new issue regarding the role of bone scanning in multiple myeloma (Edwards). The mechanisms responsible for positive scintigraphy in multiple myeloma may be an increase in bone surface area (Whaner), or osteoblastic activity present at the edge of a lytic lesion. The presence of such lesions in patients with myeloma might select a subgroup that will respond to Sr-89 therapy. However, fractures and infractions (local breakdown of trabecular structure) are the more common etiology for osteoblastic activity (Whaner) and pain from fractures will not respond to Sr-89 therapy (Edwards, Silberstein).
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