Case 746 -- A 75 year-old man with back pain

Contributed by Stacey Barron, MD and William Pasculle, ScD


A 75 year-old man presented with a four week history of back pain that acutely worsened. The pain was associated with leg weakness and intermittent numbness of his feet which interfered with his ambulation and prompted him to go to seek medical attention. He denied trauma to his back and any recent falls. He had no constitutional symptoms or loss of bowel and bladder control.

His past medical history was significant for a diagnosis of non-invasive high grade urothelial carcinoma two years ago that was treated with intravesical BCG therapy. The complete details of his therapy were unknown as it was managed at an outside institution, however the patient stated that he was told by his urologist that his cancer was in remission. The patient also stated that he an elevated PSA in the past, but it has since normalized and his urologist was not concerned for prostate cancer. In addition to this history, he is also being treated for hypertension.

He is a nondrinker and he admitted to smoking an occasional cigar, but otherwise had no smoking history. He described himself as a physically active man who walks four miles a day; however, his activity had been limited due to his back pain. He is a retired attorney. His family history was non-contributory.

On his physical exam, his vitals were normal and he had normal and equal strength in all four extremities. There was no back or spine exam recorded. Pertinent laboratory values included a white blood cell count of 13.6 x 109 /L, C-reactive protein 0.117 mg/dL (Normal: < 0.748mg/dL), and ESR 25 mm/hr (Normal: < 23 mm/hr). His PSA was noted to be 5.0.

He was referred to our institution based upon an "abnormal" x-ray ordered by his primary care physician when his symptoms failed to improve. The findings on the x-ray prompted the physicians to order an MRI. The MRI demonstrated a destructive bony process involving T4 and T5 with a soft tissue tumor component extending into the surrounding paraspinal musculature and lobulated extension into the central canal posteriorly, resulting in canal distortion and lateral and ventral cord compression (Figure 1 and Figure 2). A CT of the chest/abdomen/pelvis re-demonstrated this lesion and failed to show any evidence of malignancy or metastasis elsewhere in the body. The differential diagnosis provided by the radiologist included a metastatic malignancy that included bladder, prostate and lung as well as infection.

To further evaluate this lesion, a CT-guided biopsy was performed that showed many red blood cells, moderate white blood cells, and no organisms. In addition, routine, fungal, and mycobacterial cultures of the material obtained were planted. After these nonspecific findings reported by the biopsy, the patient was taken to the operating room for exposure of T4-T6. The operative note reported that there were no signs of any significant abscess or purulence anywhere in the region. However, the T5-T6 disk space had 'brawny-looking granulomatous material' present which was cultured and sent to microbiology. The surgeon also noted bony erosions of the vertebral bodies surrounding this material. A frozen section was performed that was interpreted to be a fibrotic process with inflammatory cells with a pathologist remark of 'do not think it is carcinoma or abscess.' After this procedure, the patient returned to the operating room again for fusion of T1 to T7. Specimens for permanent pathology were submitted and histologic evaluation of the T5 and T4 vertebral bones and the T4/5 intervertebral disk demonstrated similar findings of chronic inflammation and reparative changes with no morphologic or immunohistochemical evidence of carcinoma. Special stains for bacterial, fungal and mycobacterial organisms were all negative, but the microbiology cultures were still pending.

Following the fusion surgery, the patient was discharged on vancomycin with cultures still pending.

The initial specimen from the CT-guided biopsy had a negative acid fast stain on the direct specimen therefore a mycobacterial culture in solid and liquid media were planted. Approximately four weeks later, the liquid broth culture grew rare acid fast bacilli as visualized by acid-fast stain. On Lowenstein-Jensen media, the colonies were buff, low and small (Figure 3). A DNA probe was performed that was positive for the Mycobacterium tuberculosis complex and negative for the Mycobacterium avium complex. Further biochemical testing was performed that demonstrated that this organism was niacin accumulation negative, nitrate reduction negative, and resistant to pyrazinamide.

Given the patient's clinical history, surgical findings, and culture results, what organism has been isolated?


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