Diseño de un modelo de Gestión de Conocimiento

A 58-year-old female reports pain in her elbow over the past 6 weeks. She had a recent increase in the pain 2 days ago after lifting a chair in her living room. Past medical history includes borderline hypertension and hyperlipidemia. She has lost 20 lb of weight unintentionally over the past 4 months. An x-ray and histology slides can be seen in Figures 27-1 to 27-3.

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Figure 27-1. Lateral x-ray

of the right humerus.

Figure 27-2. Biopsy specimen (100× magnifica-

tion).

Figure 27-3. Biopsy specimen (400× magnifica-

Vignette 27: Answer

Metastatic carcinoma and multiple myeloma must be considered in the workup of any patient older than 40 years with a new presentation of a destructive lesion of bone (always think mets, myeloma, lymphoma!). In this age group, metastatic disease and myeloma are 2 orders of magnitude more common than a lymphoma or primary sarcoma. Even so, the potential diagnosis of a sarcoma must be considered because the treatments for metastatic disease and sarcoma are vastly different. The goals in metastatic disease are pain control and improving or maintaining function. For nonmetastatic sarcoma, en bloc resection in an attempt to eradicate the cancer is warranted. A worst-case scenario is treatment of a presumed carcinoma with an IM device and subsequent pathology consistent with sarcoma. In this hypothetical circumstance, a previously limb- salvageable extremity may have to be amputated to gain oncologic control.

A complete history and physical exam are important. Specifically, patients should be asked about a previ- ous history of cancer and smoking. A complete description of axial and appendicular pain is necessary to determine all sites of concern. A history of pain with weight bearing is especially worrisome because this may imply an impending pathologic fracture. The common sources of primary tumors are lung, breast, kidney, prostate, thyroid, and GI. Prostate carcinoma metastases are typically blastic (as are approximately 60% of breast cancer mets). The other common tumors to metastasize present as lytic lesions (lung, thyroid, and renal). Think like a doctor, not an orthopod; ask questions pertaining to these tumors that commonly metastasize.

The initial imaging studies should consist of orthogonal plain x-rays of the entire affected bone. This will characterize the lesion, determine the extent, and assess for disease elsewhere in the bone. In the case of fractures, the x-rays should be analyzed with a high index of suspicion if the mechanism of injury is a lesser force than what is normally expected. Additional staging studies include chest, abdomen, and pelvis CT scans to search for a possible primary tumor (lung, kidney, colon) and visceral metastases (lung, liver, spleen). A bone scan helps determine if there are any other sites of osseous disease. The most common site of metastasis is the thoracic spine (remember Batson’s vertebral plexus—a means for mets to gain access to the axial skeleton via this valveless venous plexus). Areas of increased uptake on bone scan must be investigated with plain x-ray to ensure that they are not structurally significant lesions. Bone scans can be negative in multiple myeloma, and a skeletal survey may be used in its place. A full set of laboratory values are obtained because patients may have anemia, hypercalcemia, or renal failure. A serum protein electrophoresis is often drawn if a diagnosis of multiple myeloma is suspected (serum protein electrophoresis and urine protein electrophoreses—think Bence Jones proteins).

After the staging studies are completed, a tissue biopsy is required for the definitive diagnosis. The diag- nosis must be made prior to stabilization. It is common practice to plan for stabilization immediately fol- lowing confirmation of metastatic carcinoma or myeloma with a frozen section. It is imperative to consider the approach that would be used for excision if the lesion is found to be a sarcoma. The biopsy should be in line with this approach and transverse incisions should be avoided (very important concept; in general, don’t biopsy if you aren’t going to do excision). If surgical stabilization is not needed, needle biopsies can be very accurate in this scenario and do not require general anesthesia.

Histologically, carcinoma appears as atypical glands with a surrounding desmoplastic response inter- spersed between bony trabeculae. At higher power, the glands are composed of atypical cells with increased nuclear:cytoplasmic ratios and hyperchromatic nuclei characteristic of metastatic adenocarcinoma. Multiple myeloma (and plasmacytoma) appears as sheets of homogenous small, round, blue cells in a mosaic pattern.

Sites of metastatic disease and multiple myeloma are treated with radiation for disease control and pain relief. Chemotherapy is usually palliative and given to reduce the burden of disease. Bisphosphonates are commonly used to decrease the incidence of future skeletal events by inhibiting osteoclastic activity. The mechanism of bone destruction in metastatic disease is not by the tumor, but by osteoclastic activation by the receptor activator of nuclear factor-κβ (RANK) and RANK ligand interaction. Factors secreted by the tumor can directly and indirectly stimulate this pathway.

The consideration of stabilization of osseous lesions is dependent on the expected risk of pathologic frac- ture. The classic system to assess this is Mirel’s criteria (Table 27-1).

Lesions with a total score of 9 or more have an unacceptably high rate of fracture without stabilization and should be fixed. Scores of 7 or less should be observed. Vascular lesions, such as renal cell carcinoma, should be considered for preoperative embolization to reduce blood loss at the time of surgery.

A goal of surgical stabilization is to protect the entire bone in case of tumor growth or metastasis to a noncontiguous site in the same bone. The femoral neck should always be stabilized when possible, and all IM devices should be locked for rotational control. For large periarticular lesions, replacement with an arthro- plasty is usually more appropriate and definitive.

Why Might This Be Tested? Metastases are much more commonly seen by orthopedic oncologists than

primary bone tumors. These can come from many sites and often present differently. This genre of ques- tions is frequently touched upon because it requires the orthopedist to think more like a doctor and assess the whole-body situation.

Table 27-1.

MIREL'S CRITERIA