A 73-year-old, right-handed, high school-educated Japanese housewife developed polydipsia, polyuria, progressive weight loss, and increasing fatigue in the summer of 2008. A diagnosis of type 1 diabetes was made, and the patient was admitted to our hospital in February 2009 to control her diabetes. The attending physician and nurses in the ward noticed that she had difficulty mastering insulin self-injection, and she was referred to us for evaluation of possible dementia. She lived independently, and she and her family had not noticed memory problems in her daily life. She had no history of cigarette smoking, alcohol abuse, or neurological/psychiatric illness. A detailed review of the family history was unremarkable for neurologic/psychiatric illness. On examination, the patient was oriented to place, but not to time. There were no signs of mood disorders, psychiatric illness, or changes in personality or social conduct. The neurological examination was unremarkable; the only faint abnormality we detected was an irregular saccadic eye movement on lateral gaze with difficulty maintaining rightward gaze. The results of routine laboratory tests were all within normal limits except for mild hyperglycemia (serum glucose 128 mg/dl, HbA1c 7.2%). Her thyroid function was normal, and her serum levels of vitamin B1 and B12 were also normal. The serological studies indicated high titers of anti-GAD (2865.2 U/ml), anti-insulinoma associated protein (IA)-2 (45.1 U/ml), anti-thyroid peroxidase (14.5 U/ml), and anti-thyroglobulin (67.8 U/ml) antibodies. Her cerebrospinal fluid (CSF) was negative for hypercellularity, oligoclonal bands, or myelin basic protein. Her CSF was positive for anti-GAD antibodies (60.1 U/ml). The antibody specificity index (ASI = [anti-GADCSF/IgGCSF]/[anti-GADserum/IgGserum], which measures the intrathecal synthesis of anti-GAD antibodies[,]) was 3.16, while the IgG index was 0.53. The thoracic, abdominal, and pelvic CT scans showed no evidence of malignancy. An MRI of the head did not demonstrate any abnormalities other than a small and questionable lesion showing T2-hyperintensity not associated with T1-hypointensity in the left putamen. Specifically, there was no evidence of atrophy of the medial temporal lobes. The functional neuroimaging, 18F-fluorodeoxy glucose-positron emission tomography (FDG-PET) indicated bifrontal cortical hypometabolism and 123I-N-isopropyl-p-iodoamphetamine-single photon emission computed tomography (IMP-SPECT) showd concomitant hypoperfusion. Carotid Doppler ultrasonography showed mild atherosclerotic change with a maximum intima-media thickening of 2.0 mm. The EEG showed mild general slowing and bilateral temporal delta-range activity. Table summarizes the results of the neuropsychological tests. The patient' speech was fluent, and her articulation and prosody were normal. There were few literal and semantic paraphasias. However, she had apparent language problems characterized by defective auditory comprehension and defective repetition. Her score on the Japanese version of the Western Aphasia Battery AQ was 78.4. Her language problems were also apparent when comparing her WAIS-III verbal IQ to her relatively preserved performance IQ. Her executive functions were also defective; the verbal fluency, Trail making-B, and WAIS III working memory sub-items indicated low performance, while her processing speed was preserved. The memory tests revealed that the patient was mildly amnestic. Her recognition memory was relatively preserved. A five-day course of high-dose (0.4 g/kg/day) intravenous immunoglobulin (IVIg) was implemented after written informed consent was obtained. However, the symptoms, neuropsychological profile, and insulin dependence remained unchanged immediately after the treatment. Her anti-GAD antibody titers also remained high, both in her serum (2832.5 U/ml) and CSF (75.4 U/ml). No further treatment was implemented due to her withdrawal of consent. The status of her diabetes has been stable for one and a half years. No progression of neurological impairment has been demonstrated in daily life, on the neuropsychological tests, and on neuroimagings during this period.