Pain is the principal symptom of bone metastases. It is composed of a biologic and a mechanical aspect. The biologic component reflects the rate of tumor growth and biologic characteristics of the tumor. The increased blood flow and cytokines are important causes of bone pain and contribute to bone lysis. Finally, nerves within bone have recently been described; these transmit many neuropeptides such as substance P and calcitonin gene-related protein, which are involved in both pain modulation and bone metabolism.
Bone loss reduces bone strength and stiffness, increases strain, and leads to activity-related symptoms: so-called “mechanical bone pain.” Pain from mechanical insufficiency often increases after a treatment reduces turgor within the tumor. Bone collapse and even dislocation can then occur. This is seen most often in “successful” treatment of spinal lesions. Late sequelae such as osteonecrosis and fatigue fracture are other manifestations of mechanical insufficiency.
The initial pain pattern of a metastasis mimics that of primary bone tumors and osteonecrosis. The symptoms are intermittent but may be sharp and severe. Pain tends to be worst at night and maybe partially relieved by activity. As the lesions progresses, symptoms become more constant and take on more of a mechanical character.
General systemic issues are of concern in patients with skeletal metastases. Bed rest or reduced activity is frequently recommended for the bone pain of skeletal metastases. This produces general disuse and weakness. Manifestations commonly include atelectasis and thromboembolic disease. Careful screening for these conditions is imperative. Doppler ultrasound tests are convenient and sensitive to identify deep vein thrombosis. Loss of ambulatory ability is a poor prognostic factor in metastatic disease, particularly spine disease. Performance status should be specifically quantified as part of the preoperative evaluation.
Plain radiography remains the most specific test to diagnose bone diseases. Scintigraphy is extremely sensitive and practical because it can screen the entire body at one time. Certainly, any abnormality found on bone scan should be assessed with plain radiographs. Only when the diagnosis cannot be discerned from clinical information and these baseline tests should magnetic resonance imaging (MRI) be obtained.
Solitary bone lesions warrant a biopsy before treatment. Primary bone sarcomas occur in the population particularly under consideration. Lytic phases of dedifferentiated chondrosarcoma and Paget’s sarcoma can also produce pathologic fractures. These must not be confused with the pathologic fractures of metastatic disease. A firm diagnosis must be obtained before internally fixing such a fracture.
CT-guided needle biopsy is usually satisfactory when the lesion is osteolytic (diagnostic accuracy, 80%). When the lesion is osteoblastic or there is a thick overlying cortical rim, it is extremely difficult to insert a needle and obtain an adequate tissue sample. Such cases necessitate open surgical biopsy. Whether the biopsy is performed by closed or open technique, fracture risk is worsened by the new hole in the bone cortex. Weight bearing must be protected until bone healing occurs. Experimentally, this requires at least 6 weeks. Adequate tissue is necessary to perform special studies if required. For example, recently, the spectrum of Ki-1 lymphomas has been noted and these tumors frequently mimic metastatic carcinomas. Sufficient tissue for immunohistochemical studies should always be obtained.