99Tc(m)(V)DMSA scintigraphy in skeletal metastases and superscans arising from various malignancies: diagnosis, treatment monitoring and therapeutic implications

Skeletal metastases arising from a wide variety of malignancies including a few cases with superscan appearance were evaluated using (99)Tc(m) MDP bone scanning and (99)Tc(m)(V)DMSA scintigraphy. Whole body planar scans were obtained at 3 h and 24 h after injection of 740 MBq (99)Tc(m) MDP and 5 days later at similar times after injection of 555 MBq of (99)Tc(m)(V)DMSA. A qualitative as well as quantitative comparison was made between the (99)Tc(m) MDP bone scan and the (99)Tc(m)(V)DMSA scan in detection of osseous metastases. The reference methods used for discordant or equivocal lesions were correlative morphological imaging modalities, for example additional conventional radiography, CT or MRI. The present pictorial review deals with the results of qualitative analysis of the study. A total of 75 cases have been evaluated. The vignettes illustrated in the present article demonstrate avid (99)Tc(m)(V)DMSA concentration in skeletal metastases from a wide variety of malignancies and thus expand the potential therapeutic indications for 188/186 Re(V)DMSA. The study also demonstrates the valuable supporting role a (99)Tc(m)(V)DMSA scan can play in the confirmation as well as evaluation of the extent of malignant infiltration in a suspected superscan in routine skeletal scintigraphy. In addition, a (99)Tc(m)(V)DMSA scan detected a number of metastatic lesions in and around joints and regions with previous surgical intervention that were inconclusive in the bone scan. The results in a few patients who were available for repeat scintigraphy following treatment, support the convincing evidence that (99)Tc(m)(V)DMSA accumulation may be a sensitive indicator of patient response to therapy. This might have an important bearing in the context of increasing "cold" bisphosphonate usage in the treatment of skeletal metastases, where skeletal scintigraphy with a radiolabelled bisphosphonate derivative can often be fallacious because of competitive inhibition by the non-labelled form.