What’s the cause of the abnormal bone and CT scan results?
Vol.19, No.05, June 2011

A 69-year-old male presents with increasing back stiffness and back pain along with pain in his shoulders and hips. He had a previous diagnosis of prostate carcinoma 3 years ago, and has known osteoporosis. The patient recently located to the area from Kenora in Northern Ontario. A previous bone scan from 2 years prior was normal. A chest x-ray was performed that was normal.

What’s the most likely diagnosis regarding this man’s bone pathology?

a) diffuse sclerotic bony metastases from prostate carcinoma

b) typical degenerative changes in the aging skeleton

c) classic insufficiency fractures associated with osteoporosis

d) extensive bony involvement from blastomycosis

e) multiple myeloma


Figures 1: A total body nuclear medicine bone scan (NMBS) revealing diffuse abnormal patchy increased uptake in multiple bones of the axial and proximal appendicular skeleton.
ANSWER
Solution to Analyze This!

a) diffuse sclerotic bony metastases from prostate carcinoma

The total body nuclear medicine bone scan shown in Fig. 1 and the CT image from Fig. 2 reveal diffuse abnormal sclerotic changes throughout many bones of the axial and proximal appendicular skeleton, without overt bone destruction, break-through or collapse.

Typical degenerative changes in an aging skeleton may include sclerotic changes in the subchondral bone around joints, like the disc spaces, hips and shoulders, but the CT clearly shows the sclerosis is more extensive involving entire vertebral bodies in some areas, and in the pelvis bones distant to joint spaces. This is not a viable diagnosis in this case. Osteoporotic insufficiency fractures can reveal increased sclerosis due to osteoblastic healing, or from impaction of vertebral bodies, but the CT also shows relative preservation of the vertebral body heights. No definite fractures are present. Classic insufficiency fractures would include wedge compression fractures of vertebral and unilateral or bilateral vertical sacral fractures (not shown on CT), but no fractures were present.

Blastomycosis is a relatively rare fungal infection acquired via inhalation in endemic areas. The fungus resides in moist soil, especially near rotting vegetation. Endemic areas include the central and southeastern U.S., India, Israel, Saudi Arabia, parts of Africa, Northern Canada and around the Great Lakes. The region of Kenora in Northern Ontario has been recognized as a particular hot spot for blastomycosis infections. The fungus can involve the skeleton diffusely and can produce patchy sclerosis; however, the lesions are typically more aggressive in appearance, often with overt bone destruction and periosteal reaction, which is not present in our patient. In most patients with bony blastomycosis, the lungs are diffusely abnormal as well, whereas the chest x-ray was noted as normal in our patient. Considering this man’s residence in Kenora, this isn’t an unreasonable diagnosis to consider, but it would be highly unlikely and certainly not the “most likely diagnosis.” Although 3% of multiple myeloma cases can exhibit patchy diffuse sclerotic bone changes, the vast majority with this condition present with diffuse small punched out lytic bone lesions (giving an appearance of moth-eaten bones). An atypical presentation of this otherwise fairly common condition would still be less likely than typical metastatic disease from a known prior malignancy (prostate cancer).

Prostate cancer is the most common malignancy of Canadian men, affecting 1 in 6 in their lifetime. It’s the third most common cause of death from cancer (after lung and colon) overall and the most frequent cause of cancer death in men over age 75 years. It’s rarely diagnosed under the age of 40. When prostate cancer spreads, it most often involves the skeleton, although regional pelvic lymph nodes are frequently involved as well. Once this cancer has spread to the bones, it’s considered incurable, but there are many ways to slow the progress of the disease and reduce symptoms.

The imaging modality of choice to assess for prostate metastases is a nuclear medicine bone scan, with or without SPECT imaging. Bone scans are sensitive for initial diagnosis although aren’t specific, and are not optimal for assessing response to treatment. For institutions that offer it, 18F-NaF PET scanning has been shown to have a high sensitivity for detecting bone metastases is far more valuable in assessing response to treatment. PET scans are almost certainly the future imaging modalities of choice in cancer detection, metastatic disease detection and follow-up. How far away that future is, is still difficult to predict.

References

  1. Eisenberg RL. Am J Roengtenol 2009;193:W79-94.
  2. Kelloff GJ et al. AJR 2009;192:1455-70.
  3. Schuster DM et al. Journal of Nuclear Medicine 2007;48:56-63.
  4. Stacey, GS et al. AJR 2006;186:967-76.
  5. Angtuaco EJC et al. Radiology 2004;231:11-23.
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Figure 2: Coronal reconstruction of abdominal-pelvic CT (on bone window), revealing extensive sclerotic changes in multiple vertebrae and pelvic bones.
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