Presumptive Late-Onset Ankylosing Spondylitis Simulating Osteoblastic Skeletal Metastasis in a Patient With a History of Prostate Carcinoma: A Diagnostic Challenge

Abstract

Objective: The purpose of this report is to present a presumptive case of ankylosing spondylitis with late stage progression that simulated osteoblastic metastasis in a patient with a history of prostate carcinoma.

Clinical features: A 67-year-old white man presented to a chiropractic clinic complaining of severe and worsening acute low back pain and right foot "numbness." Further questioning also revealed a history of prostate carcinoma.

Intervention and outcome: Imaging examination revealed a sclerotic pedicle and increased uptake of radiopharmaceutical on a nuclear medicine bone scan highly suggestive of osteoblastic skeletal metastasis. Further evaluation, however, revealed that the bone sclerosis was not the result of skeletal metastasis, but more consistent with a seronegative spondyloarthritis such as ankylosing spondylitis.

Conclusion: This report describes a presumptive case of ankylosing spondylitis simulating skeletal metastasis in a patient with a past medical history of prostate cancer. This atypical presentation illustrates the inherent uncertainty of diagnosis and how that uncertainty can be challenging in clinical practice. It also reinforces that it is critical for healthcare providers to consider a wide spectrum of differential diagnoses to avoid misdiagnoses and inappropriate interventions.

Keywords: Ankylosing spondylitis; Chiropractic; Diagnosis; Neoplasm metastasis; Spondylarthritis.

Fig 1

Anteroposterior (A) and lateral (B) lumbar spine radiographs revealing an osteosclerotic lesion involving the right pedicle (arrow) and vertebral body of T12. Other radiographic findings include bilateral osseous ankylosis of the sacroiliac joints, mild disc space narrowing and osteophytes at multiple levels (most notably at L3-4, L4-5, and L5-S1), mild degenerative spondylolisthesis at L3-4 and L4-5, slight right lumbar convexity, and bilateral concentric narrowing with axial migration of the hip joints. Of incidental note are multiple surgical staples located along the anteroinferior aspect of the pelvic basin from a previous prostatectomy. (C) Spot view of the sacroiliac joints revealing osseous ankylosis bilaterally.

Fig 2

Radionuclide whole-body bone scan, after injection of 866 MBq of technetium 99m methylene disphosphonate, shows abnormal osseous activity evidenced by increased uptake at the T12 vertebra on the right (arrows). Note also the increased uptake within the bilateral tibiae (distal on the right, proximal on the left). All other sites of uptake in the lower lumbar vertebrae and several other joints likely indicate degenerative/arthritic changes. It is unclear the significance of the increased uptake in the tibiae.

Fig 3

Axial CT scan showing osteosclerosis involving the right half of the vertebral body and pedicle of T12.

Fig 4

Sagittal T1-weighted MR images of the thoracolumbar spine, without (a) and with (b) gadolinium contrast, revealing abnormal signal intensity within the T12 vertebra that enhances only slightly after gadolinium administration.

Fig 5

Axial T1-weighted MR images of the T12 vertebra, without (A) and with (B) gadolinium. Note the “mottled” appearance (ie, hypo- and hyper-intense foci of mixed signal intensity) within the right half of the vertebral body and pedicle of T12.