Elsevier

Mayo Clinic Proceedings

Volume 83, Issue 8, August 2008, Pages 917-922
Mayo Clinic Proceedings

ORIGINAL ARTICLE
Occult Malignancy in Patients With Suspected Paraneoplastic Neurologic Syndromes: Value of Positron Emission Tomography in Diagnosis

https://doi.org/10.4065/83.8.917Get rights and content

OBJECTIVE

To determine the value of positron emission tomography (PET) in diagnosing occult malignancies in patients with paraneoplastic neurologic syndromes (PNSs) at Mayo Clinic's site in Rochester, MN.

PATIENTS AND METHODS

We retrospectively reviewed the medical charts of all 107 patients who underwent PET from January 1, 2000, to July 31, 2006, for the indication of suspected PNS. Three patients did not meet inclusion criteria. PET results were considered positive if increased fludeoxyglucose F 18 uptake indicated malignancy (24 patients). Results from computed tomography were interpreted as positive if any suspect lesion was consistent with malignancy (26 patients).

RESULTS

One hundred four patients with PNS were identified from the PET central database; 73 patients had at least 1 positive result for paraneoplastic antibody, and 31 had antibody-negative PNS. Malignancy was confirmed pathologically in 10 patients, of whom 8 had positive PET results. There were 2 cases of confirmed malignancy (fallopian tube adenocarcinoma and spindle cell uterine carcinoma) for which PET results were negative. Two patients with positive PET results declined biopsy. Computed tomography was able to identify 3 of the 10 malignancies detected. Five cases of malignancy were detected only by PET. All patients with confirmed malignancy had positive results for at least 1 paraneoplastic antibody. One patient with positive results for PNS antibody and negative PET results was diagnosed as having small cell carcinoma on a follow-up PET scan after 27 months. PET had sensitivity, specificity, positive predictive value, and negative predictive value of 80%, 67%, 53%, and 88%, respectively.

CONCLUSION

PET scan was shown to be more sensitive than computed tomography for detecting occult malignancy (confirmed by positive test results for autoantibody) among patients with suspected PNS. The greatest clinical utility of PET could be in its high negative predictive value.

Section snippets

PATIENTS AND METHODS

After approval by the Mayo Clinic Institutional Review Board, the nuclear medicine electronic database at Mayo Clinic's site in Rochester, MN, was queried for PNS as an indication for PET. A total of 107 patients were identified in the database from January 1, 2000, to July 31, 2006.

RESULTS

Of the 107 patients identified from the PET database, 104 met the inclusion criteria.15 Three patients were excluded because 1 had metastasis to the brain and 2 did not have a final diagnosis of PNS. Baseline characteristics of all the patients are described in Table 1. Seventy-three patients had a positive result for at least 1 paraneoplastic antibody, and 31 had a clinical diagnosis without a detectable paraneoplastic antibody. PET results were positive in 24 patients, 17 of whom had a

DISCUSSION

Patients with suspected PNS present a diagnostic dilemma because of the difficulty in detecting a suspected occult malignancy with conventional testing. Although PET has been recommended and used to detect occult malignancies in this patient population, its diagnostic utility has not been well defined.12

We have scrutinized the clinical utility of PET in patients with suspected PNS. Data suggest that PET has a better NPV (88%) and therefore is a better diagnostic tool to rule out occult

CONCLUSION

PET is substantially more sensitive than CT for detecting occult malignancy in patients with suspected PNS. Occult malignancy was detected only in patients with PNS who had a positive test for autoantibody. Patients with suspected PNS and no detectable malignancy should be followed up every 6 to 12 months for a period of at least 5 years as recommended by the European Federation of Neurological Societies. The utility of follow-up CT or PET in these patients could not be determined because of

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These data were presented as a poster at the 12th World Conference on Lung Cancer; Seoul, South Korea; September 2-6, 2007.

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