Paraneoplastic cerebellar degeneration (PCD) is a paraneoplastic neurological syndrome encountered in patients with malignant tumors. Underlying tumors that are frequently detected include small cell lung cancer, gynecological cancers, breast cancers, and malignant lymphoma. ' We describe here a patient with PCD in whom no underlying tumor could be detected despite extensive exploration until finally the occult tumor was visualized by positron emission tomography with "F-fluorodeoxyglucose (FDG-PET). After surgical removal of the tumor, progression of cerebellar ataxia ceased and the anti-Yo antibody titer decreased.A 7 1-year-old woman had been transferred to our hospital with rapidly progressive dysarthria and ataxia. Results of physical examinations were normal. Neurological examinations showed horizontal gaze nystagmus, ataxic dysarthria, and marked limb and truncal ataxia. Deep tendon reflexes were normal with no motor or sensory impairment, but bilateral Chaddock reflexes were positive. Blood analysis was normal and tumor markers, carcinoembryonic antigen, a-fetoprotein, CA19-9 and CA125, were all within normal ranges. Chest radiography was unremarkable, and head magnetic resonance imaging showed atrophy of the posterior fossa structures, especially the vermis. Serum anti-Yo antibody titer measured by enzyme-linked immunosorbent assay2 was high at 0.481 (control, 0.056 2 0.008). Western blot analysis of rat cerebellar homogenate incubated with the patient's serum IgG revealed a 58-kd band. Immunohistochemistry showed that the patient's serum IgG strongly reacted with Purkinje cell cytoplasm of the rat.Paraneoplastic cerebellar degeneration was suspected, but lung computed tomography, abdominal computed tomography, intrapelvic computed tomography, abdominal echography, gastrointestinal endoscopy, vesicography, gallium scan, and gynecological examinations revealed no evidence of tumors. Finally, whole-body positron emission tomography (ECAT-EXACT, Siemens) for 40 minutes from 45 minutes after intravenous injection of FDG (7 mCi) revealed localized accumulation in the caudal portion of the lower pole of the left kidney (Fig). The standardized uptake value3 was high at 4.54 (control for nonmalignant material, 1.01 L 0.26, n = lo), a value that ruled out an inflammatory lesion. Abdominal angiography confirmed a vascular-rich tumor; and at surgical operation, a 28 X 22-mm undifferentiated adenocarcinoma at the omentum, rich in tubular structure, was removed. After the operation, progression of cerebellar ataxia ceased. Anti-Yo antibody titer declined to 0.304 and showed no increase 8 months later.In paraneoplastic cerebellar degeneration, neurological signs and symptoms often precede those of malignancy.* However, early detection of the primary tumor is often difficult, although critically i m p~r t a n t . ~ We suggest that, in patients with elevated anti-Yo antibody, in whom paraneoplastic syndrome is suspected, FDG-PET can be useful to detect the occult tumor.We thank Drs. Keiko Tanaka and Takashi Inuzuka, ...

No abstract