99mTc-HDP pinhole SPECT findings of foot reflex sympathetic dystrophy: radiographic and MRI correlation and a speculation about subperiosteal bone resorption.

Reflex sympathetic dystrophy (RSD) is a common rheumatic disorder manifesting painful swelling, discoloration, stiffening and atrophy of the skin. Radiographic alterations include small, spotty subperiosteal bone resorption (SBR) and diffuse porosis, and MR imaging shows bone and soft-tissue edema. The purposes of current investigation were to assess 99mTc HDP pinhole SPECT (pSPECT) findings of RSD, to correlate them with those of radiography and MRI and to speculate about causative mechanism of SBR which characterizes RSD. pSPECT was performed in five patients with RSD of the foot. pSPECT showed small, discrete, spotty hot areas in the subperiosteal zones of ankle bones in all five patients. Diffusely increased tracer uptake was seen in the retrocalcaneal surface where the calcaneal tendon inserts in two patients with atrophic RSD. pSPECT and radiographic correlation showed spotty hot areas, that reflect focally activated bone turnover, to closely match with SBR. Further correlation with MRI showed both spotty hot areas and SBR to coincide in location with the insertions of ligaments and tendons, onto which pulling strain is constantly exerted. In contrast, the disuse osteoporosis in unstrained bones did not show any more significantly increased tracer uptake than normal cancellous bones.