The role of [F-18]fluoro-2-deoxyglucose-PET scanning in the diagnosis of paraneoplastic neurological disorders

The detection of an occult tumour in a patient with a suspected paraneoplas tic neurological disorder (PND) may be difficult because of the limitations of conventional imaging techniques. [F-18]fluoro-2-deoxyglucose-PET (FDG-P ET) can visualize a small tumour anywhere within the body. We retrospective ly reviewed the case notes of 43 unselected patients with suspected PND ref erred for FDG-PET scanning to determine how useful this technique was when conventional imaging was negative. All patients had undergone standard radi ological investigations and bronchoscopy (where appropriate) prior to PET s canning. There were discrete areas of hypermetabolism suggestive of maligna ncy (positive) in 16 patients (37%). A tissue diagnosis of cancer was subse quently made in seven patients (two at post-mortem), further radiological s tudies were suggestive of cancer in one patient, one patient subsequently p resented with a metastatic deposit which was biopsied, and four patients di ed shortly afterwards without a post-mortem. In three patients, subsequent investigations were negative for cancer. Serum anti-neuronal antibodies wer e present in 43% and CSF oligoclonal bands were present in 46% of patients with positive PET scans compared with 16 and 26%, respectively, in PET-nega tive patients, but this was not significant. Only one patient with a negati ve scan has been diagnosed subsequently as having malignancy on prolonged f ollow-up. These findings confirm that FDG-PET scanning is a useful techniqu e in the detection of small tumours in patients with suspected PND. False p ositives and false negatives do occur, but at a sufficiently low frequency to justify the clinical usefulness of this technique.