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Paget's disease should be considered in the differential diagnosis of spinal cord compression when MRI is suggestive of malignant disease.
A woman of 60 had for eighteen months noticed altered sensation in her legs, beginning in the feet and progressing up both legs to involve the trunk to the level of her breasts. Her legs were also weak and stiff. She had become increasingly unsteady and had fallen several times; for the past year she had used a stick to walk, and for the last month a frame. Recent new features were urinary urgency and occasional incontinence. There was no history of acute back pain but she reported a longstanding dull ache in the lumbar region. She had experienced no disturbance of vision or speech or swallowing.
On general examination the only noteworthy finding was a raised body mass index. The abnormal findings in the nervous system were bilateral weakness of hip flexion and knee flexion, MRC grade 4/5, with brisk lower limb reflexes, adductor jerks and extensor plantar responses consistent with a spastic paraparesis. She had bilateral sensory change to light touch and pinprick to the level of the 4th thoracic segment. Joint position sense and vibration were lost to her ankles. The combination of upper motor neuron signs in the legs, normal findings in the arms and a sensory level suggested a lesion of the thoracic spinal cord. MRI (Figure 1) gave a low T1 and T2 weighted signal in the 1st, 3rd and 4th thoracic vertebrae with cord compression at the 3rd and 4th and an associated bright cord signal. The cord narrowing was principally due to posterior epidural tissue of mixed low and high T1-weighted and T2-weighted signals. Fat-saturated T1-weighted images indicated the bright portion of this tissue to be epidural fat.
Blood tests were normal apart from an alkaline phosphatase of 488 IU/L and an erythrocyte sedimentation rate of 12 mm/h. Protein electrophoresis was normal, as were the tumour markers carcino-embryonic antigen, Ca125, Ca199 and alpha fetoprotein. CT of the chest, abdomen and pelvis showed multiple areas of bony sclerosis and lucency, without obvious expansion, within many of the vertebral bodies, both iliac bones and the right 7th rib. There was no evidence of primary malignancy. CT of the thoracic spine (Figure 2) revealed expansion and mixed sclerosis and lysis of the bodies and posterior elements of the 1st, 3rd and 4th thoracic vertebrae. There was pronounced stenosis of the bony canal, mainly due to overgrowth of the posterior elements. The expansion of the bone seen on CT is characteristic of Paget's disease. The patient was treated with intravenous zoledronate and showed some improvement at 6-week follow-up.
Cord compression in Paget's disease of bone is due to both mechanical impingement and vascular distortion.1 Histo-pathologically, an increase in multinucleated osteoclasts results in bone resorption with lytic lesions, and is followed by osteoblastic activity and formation of abnormal new bone that is highly vascular, fragile and sclerotic. There is hyperaemia of the surrounding tissues. Osteoblasts are seen around thick and vascular trabeculae of new bone, and there may be wide seams of uncalcified osteoid. The end result is dense bony sclerosis, with the thickened, deformed bone characteristic of Paget's disease. In the patient reported here, epidural lipomatosis contributed to the cord narrowing. The signal characteristics of the abnormal bone on MRI may be indistinguishable from sclerotic bone metastases. However, expansion of the bone in association with sclerosis and lysis, well seen on plain radiographs or CT, is diagnostic of Paget's disease.