Patient 1 is a 62-year-old man with known chronic tophaceous gout who was seen in 1997 for an annual check-up that revealed an enlarged prostate and noninflamed multiple gouty tophi, the largest of which involved the left pre-patellar bursa. Patient 2 is a 61-year-old man with known advanced right-knee osteoarthritis and prostate cancer that had been treated with cryoablation in May 2000.
Patient 1 is a 62-year-old man with known chronic tophaceous
gout who was seen in 1997 for an annual check-up that revealed an
enlarged prostate and noninflamed multiple gouty tophi, the largest
of which involved the left pre-patellar bursa. He also had an
elevated prostate specific antigen (PSA) for which he underwent a
prostatectomy. Three years later, he presented with an elevated PSA
and an indium-111-labeled capromab pendetide (ProstaScint, Cytogen
Corp., Princeton, NJ) scan was ordered. The ProstaScint scan showed
increased activity involving the para-aortic and right iliac lymph
nodes, indicating metastatic prostate cancer. It also demonstrated
an area of increased activity involving the left prepatellar region
Patient 2 is a 61-year-old man with known advanced right-knee
osteoarthritis and prostate cancer that had been treated with
cryoablation in May 2000. On physical examination, he was noted to
have an enlarged prostate and was suspected to have extracapsular
extension of disease. The right knee showed no signs of active
inflammation. A ProstaScint scan performed as part of his work-up
revealed activity limited to the prostatic bed with no evidence of
extra prostatic nodal activity. Increased activity in the region of
the patient's right knee was noted incidentally (Figure 2).
Patient 1: Chronic tophaceous gout, causing increased
ProstaScint accumulation in the prepatellar bursa.
Patient 2: Advanced osteoarthritis, causing increased activity
on ProstaScint scan.
These cases demonstrated positive ProstaScint scans, which did
not prove to be carcinoma.
It is important to recognize other causes of increased activity
with this radionuclide. ProstaScint scan is a technically demanding
procedure with several potential pitfalls: suboptimal quality
control of the camera, suboptimal patient preparation, inadequate
imaging time, and inaccurate computer processing. Therefore, it is
best performed and interpreted at sites with experience and
The gamut for false-positive activity with ProstaScint scan
includes such common causes: injection site and its regional
draining lymph nodes, gastrointestinal (GI) tract activity,
tortuous vessels, and misinterpreting expected areas of
radiopharmaceutical biodistribution (such as the liver, spleen,
bone marrow, salivary gland, male genitalia, blood pool activity,
kidney, and bladder). False-positive activity may also have some
uncommon causes: renal cell carcinoma,
gout, and osteoarthritis.
These are the first reports of false-positive ProstaScint scans
from joint disease. There have been a few reported cases of
abnormal uptake of ProstaScint from the causes listed above.
Indium-111-labeled capromab pendetide (ProstaScint) is a new
radiopharmaceutical that is FDA-approved for the imaging of
prostate cancer patients at high risk for metastatic disease and
for patients who have had a prostatectomy and present with a rising
serum PSA level.
Capromab pendetide is a whole murine monoclonal antibody
directed against prostate membrane specific antigen (PMSA), a
transmembrane glycoprotein expressed by prostate epithelial cells.
Prostate membrane specific antigen is higher in prostate
adenocarcinoma cells than in nonmalignant cells, and higher in
metastatic lesions than in the primary lesion. Typically,
ProstaScint scans has a biodistribution of activity involving the
liver, spleen, kidneys, bone marrow, male genitalia, and blood
pool. It is excreted in the GI tract. It is used to stage newly
diagnosed prostate cancer and to identify residual disease, local
recurrence, and metastasis in post-prostatectomy patient.
It enables more accurate disease staging and monitoring than is
afforded by other imaging modalities, such as CT and MRI.
Gout encompasses a group of disorders that occur alone or in
combination and include hyperuricemia, arthritis, tophaceous
deposition of urate crystals in and around joints, interstitial
deposition of urate crystals in renal parenchyma, and urolithiasis.
Approximately 10 years after the first acute attack, tophi become
apparent on physical examination, as in the first case.
Osteoarthritis also exhibits a verity of clinical expressions that
typically lack clinical signs of inflammation. We postulate that
the increased uptake was from low-grade clinically occult
inflammation at the sites of these patient's joint disease.
False-positive ProstaScint scans occur from numerous causes.
These are the first reported cases of joint disease that caused
false-positive studies. Radiologists interpreting these scans need
to be aware of the causes of false-positive scans.