Atypical presentation of Paget's disease on bone scintigraphy

A 76-year-old man with a history of ankylosing spondylitis (AS) was evaluated for possible Paget's disease (PD) based on an elevated alkaline phosphatase level of 197 U/l (normal, 36 to 126 U/l) and a urinary hydroxyproline level of 68 mg per 24 hours (normal, 5 to 65 mg). Roentgenograms of the posteroanterior and lateral chest, lateral lumbar spine, and sacroiliac joints revealed marked kyphosis within the thoracic spine and a flowing anterior syndesmophyte and ankylosis of the sacroiliac joints consistent with AS. The films also showed expansion, prominent trabecula, end cortical thickening of affected thoracic ribs, and L2-L3 vertebral bodies, consistent with PD. Additional changes of PD were seen in the T7-T10 vertebral bodies and the anterior syndesmophyte bridging these levels. Anterior and posterior whole-body scintiscans were obtained after intravenous administration of 25 mCi Tc-99m MDP. The scintigrams showed typical increased uptake in the T7-T11 and L2-L3 vertebrae, consistent with PD. In addition, they demonstrated increased uptake in the posterior seventh through tenth ribs bilaterally, corresponding in location to the pagetoid changes seen on the roentgenograms. This bone scan appearance is unusual in that unlike the typical PD presentation (i.e., extension distally from the articular surface of the bone without crossing of the joint), PD in this case extended across joints fused by AS.