We here present a case of 44-year-old woman, a carrier of human T-lymphotrophic virus type-1 (HTLV-1), who suffered from
limbic encephalitis and
breast cancer. In December 1997, the patient's behavior became abnormal. Three weeks later, she became markedly forgetful. At that time neurological examinations revealed that she had anterograde and
retrograde amnesia, disorientation, and confabulation, although her consciousness was clear. Anti-Hu and
anti-Yo antibodies and
antinuclear antibodies in the serum were negative. Flow cytometric study of the peripheral blood lymphocytes showed an increased percentage of CD3+CD25+ cells, although the percentages of CD4+CD45RA+ and CD4+CD45RO+ cells were normal. Lymphocytic responses to
phytohemagglutinin or
concanavalin A were normal. Anti-HTLV-1 antibody was positive both in the serum and in the cerebrospinal fluid (CSF). The level of
immunoglobulin G was high and two
oligoclonal immunoglobulin G bands were positive in the CSF. Cytological study of the CSF showed no atypical cells. Findings for herpes simplex virus type I and II DNAs were negative with polymerase chain reaction in the CSF. There was no elevation of antibody titers against viruses including herpes simplex virus, cytomegalovirus, and measles virus, either in the serum or the CSF. Magnetic resonance imaging showed signal abnormalities in the medial portions of both temporal lobes, in particular, in the bilateral hippocampus. Six weeks after the onset, a cancerous
tumor in her right breast was detected and removed by open surgery. The pathological diagnosis was invasive
ductal carcinoma with neuroendocrine features. After
mastectomy, anterograde and
retrograde amnesia and disorientation mildly improved. The follow-up magnetic resonance imaging showed that signal abnormalities in the medial portions of both temporal lobes decreased and that the bilateral hippocampus became atrophic. We diagnosed the present case as
paraneoplastic limbic encephalitis. There has been only one case report of
limbic encephalitis associated with
breast cancer.