A case of slowly progressive anti-Yo-associated paraneoplastic cerebellar degeneration successfully treated with antitumor and immunotherapy.

We report a case of slowly progressive anti-Yo-associated paraneoplastic cerebellar degeneration (PCD) with breast cancer in a 54-year-old woman. The symptoms of limb and truncal ataxia, and dysarthria gradually progressed during the course of 1 year, and the modified Rankin scale (mRS) score was 2. A mastectomy with sentinel lymph node resection was performed for the breast cancer. No malignant cells were found on histopathological examination of the lymph node. Combination chemotherapy with adriamycin and cyclophosphamide (AC) prevented neurologic deterioration. However, subsequent treatment with trastuzumab and paclitaxel did not prevent progression of the symptoms (mRS score 3). Brain magnetic resonance imaging showed atrophy of the cerebellar hemispheres without brain stem atrophy. Anti-Yo antibody was detected in the serum, which led to a diagnosis of anti-Yo-associated PCD. We resected an enlarged axillary lymph node, which was found on computed tomography. The histopathological analysis of the lymph node revealed foreign body granuloma, which suggested an association with necrotic malignant tissue. Following additional tegafur-uracil therapy and two courses of intravenous immunoglobulin (IVIg), the cerebellar signs and symptoms gradually improved (mRS score 2). The clinical course shows that PCD can present as a slowly progressive cerebellar symptom. We propose an active treatment for anti-Yo-associated PCD consisting of tumor resection, combined chemotherapy, and IVIg.