How are coexistent opportunistic infections differentiated from pulmonary Kaposi sarcoma (KS) on imaging?

Updated: Mar 13, 2019
  • Author: Ali Nawaz Khan, MBBS, FRCS, FRCP, FRCR; Chief Editor: Eugene C Lin, MD  more...
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Answer

Approximately two thirds of patients with KS presenting with new pulmonary abnormalities have coexistent opportunistic infections. Differentiating KS from opportunistic infections is not always possible by using anatomic imaging.

Gallium-67/thallium-201 (67Ga/201Tl) radionuclide imaging has been used to distinguish AIDS-related KS from other pulmonary disease processes. KS is 201Tl avid, but it does not take up 67Ga. Abnormal chest radiographic findings in association with negative 67Ga findings suggest the presence of pulmonary KS.

Indium-111–labeled polyclonal immunoglobulin is taken up by infection but not by KS or lymphoma. Indium-labeled liposomes have been shown to accumulate in KS, but uptake has also been reported with lymphoma. [16]

Radionuclide scans are a useful adjunct to radiographs and CT scans, particularly when radiographic findings are complex and when the exclusion of opportunistic infections that complicate KS is important. Indium-11-labeled polyclonal immunoglobulin uptake has a sensitivity of 97% in the diagnosis of AIDS-related pulmonary infections; by contrast, chest radiography has a sensitivity of 62%. Although HRCT is superior to chest radiography, some have suggested that HRCT may be less sensitive than 67Ga scintigraphy in the assessment of suspected Pneumocystis jiroveci pneumonia (PCP).

A false-positive rate of 15% has been reported for gallium scanning in the assessment for P jiroveci pneumonia. Other infections and lymphomas may also take up gallium. It has been suggested that thallium uptake may occur in lymphoma and infections such as PCP.


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