The substance 99mTc-labeled depreotide (DP) is a novel radiopharmaceutical that binds to somatostatin receptors. Somatostatin-based nuclear scintigraphy was initially utilized in the evaluation of neuroendocrine tumors. Somatostatin receptors, however, also are overexpressed in other malignant and inflammatory conditions. With nuclear imaging techniques, 99mTc-DP represents a tool for evaluating pulmonary nodules in order to gauge the probability that the lesion is malignant. Currently, 99mTc-DP scanning is formally approved for use in this setting and is reported to have a sensitivity of 95% and a specificity of 85%. http://www.medicine-against-diabetes.net/
Causes for false-positive 99mTc-DP include hamartomas, acute infection, and granulomatous diseases. Sarcoidosis, a disease characterized by the presence of non-necrotizing granulomas, has anecdotally been reported to result in positive 99mTc-DP scan findings. In fact, somatostatin receptors have been found on the epithelioid cells and giant cells that comprise the sarcoid granuloma. Few prior studies have evaluated somatostatin receptor scintigraphy in sarcoidosis. Lebtahi and colleagues performed In-penetreotide (P) scans in 18 subjects with sarcoidosis. They noted that the findings of these scans were often positive and that areas of activity identified on nuclear imaging correlated with those found on chest radiographs (CXRs). In-P, though, failed to identify 40% of the sites of extrapul-monary sarcoidosis.
Traditionally, Ga has been utilized in scanning for the detection of sarcoidosis. However, Ga-based imaging modalities have significant limitations. First, patients must be injected with the radiolabeled material at least 48 to 72 h before image acquisition. Second, there is significant interobserver variability in the interpretation of Ga scans.- Third, although certain patterns noted on Ga scans are considered to be unique to sarcoidosis (eg, the lambda-panda pattern), the overall sensitivity and specificity of Ga varies significantly. Some researchers have reported that this tool is highly accurate, while others have failed to observe similar findings. Thus, at present Ga scanning is generally considered to have a limited role in the evaluation and management of sarcoidosis.