Chapter 7-5: Back Pain Due to Metastatic Cancer

TEXTBOOK PRESENTATION

The classic presentation is the development of constant, dull back pain that is not relieved by rest and is worse at night in a patient with a known malignancy.

DISEASE HIGHLIGHTS

1. Bone metastases can be limited to the vertebral body or extend into the epidural space, causing cord compression.

2. Pain can precede cord compression by weeks or even months, but compression progresses rapidly once it starts.

   Cancer + back pain + neurologic abnormalities = an emergency.

3. Malignancy causes < 1% of back pain in general but is the cause in most patients with active cancer who have back pain.

4. Most common sources are breast, lung, or prostate cancer.

   1. Renal and thyroid cancers also commonly metastasize to bone.

   2. Myeloma and lymphoma frequently involve the spine.

5. Metastases are in the thoracic vertebrae in 60% of cases, in the lumbar spine in 25%, and in the cervical spine in 15%. Up to one-third of patients have multiple spine metastases.

6. Blastic lesions are seen with prostate cancer, small cell lung cancer, Hodgkin lymphoma.

7. Lytic lesions are seen with renal cell, myeloma, non-Hodgkin lymphoma, melanoma, non–small cell lung cancer, thyroid cancer.

8. Mixed blastic and lytic lesions are seen with breast cancer and GI cancers.

EVIDENCE-BASED DIAGNOSIS

1. History and physical exam

   1. Previous history of cancer has an LR+ of 14.7 for the diagnosis of vertebral metastasis as a cause of back pain.

   2. The absence of nocturnal pain reduces the probability that cancer is causing the back pain (LR– 0.17).

   3. Table 7-7 lists the historical and physical exam findings associated with low back pain due to cancer.

Cancer is not likely to be the cause of back pain if the patient is younger than 50 years, has no history of cancer, has not experienced unexplained weight loss, and has not failed conservative therapy.

2. Imaging

   1. Plain radiographs

      1. Lytic lesions are not visible until about 50% of trabecular bone is lost.

      2. Blastic lesions can be seen earlier on radiographs than lytic lesions.

      3. Sensitivity, 60%; specificity, 96–99.5%

      4. LR+, 12–120; LR–, 0.4–0.42

   2. CT scan: Sensitivity and specificity for diagnosing metastatic lesions are unknown.

   3. MRI

      1. Sensitivity, 83–93%; specificity, 90–97%

      2. LR+, 8.3–31; LR–, 0.07–0.19

   4. Bone scan

      1. Sensitivity, 74–98%; specificity, 64–81%

      2. LR+, 3.9–10; LR–, 0.1–0.32

      3. Better for blastic lesions than lytic lesions; myeloma, in particular, can be missed on bone scan.

MRI scan is the best test for diagnosing or ruling out cancer as a cause of back pain and for determining whether there is cord compression.

3. Laboratory tests: the erythrocyte sedimentation rate (ESR) is sometimes helpful.

   1. ≥ 20 mm/h: sensitivity, 78%; specificity, 67%; LR+, 2.4

   2. ≥ 50 mm/h: sensitivity, 56%; specificity, 97%; LR+, 19.2

   3. ≥ 100 mm/h: sensitivity, 22%; specificity, 99.4%; LR+, 55.5