Cognitive decline in a patient with anti-glutamic acid decarboxylase autoimmunity; case report

We describe the clinical, neuropsychological, and neuroradiological findings of a 73-year-old female with cognitive dysfunction and type 1A diabetes. Observation and neuropsychological studies revealed linguistic problems, short-term memory disturbance, and frontal dysfunction. MRI showed no significant lesion except for confluent small T2-hyperintensity areas localized in the left basal ganglia. 18F-fluorodeoxy glucose-positron emission tomography (FDG-PET) and 123I-N-isopropyl-p-iodoamphetamine-single photon emission computed tomography (IMP-SPECT) studies showed bifrontal hypometabolism and hypoperfusion. Immunomodulating therapy with intravenous high-dose immunoglobulin resulted in no remission of the cognitive symptoms.Cognitive dysfunction may develop as an isolated neurological manifestation in association with type 1A diabetes and anti-GAD autoimmunity. A systematic study with extensive neuropsychological assessment is indicated in patients with type 1 diabetes and anti-GAD autoimmunity.Glutamic acid decarboxylase (GAD) is the biosynthesizing enzyme of the neurotransmitter γ-aminobutyric acid (GABA). Antibodies against GAD cause neurological syndromes[1], including stiff person syndrome (SPS)[2], cerebellar ataxia[3], and limbic encephalitis[4] as well as type 1 diabetes[5]. Behavioral and cognitive problems may be associated with SPS[6], limbic encephalitis[7], or cerebellar ataxia, and some of the psychiatric symptoms that have been reported in SPS[8] are considered to be related to dysfunction of the GABAergic system. However, it is not known whether dementia appears as the sole neurological manifestation associated with anti-GAD antibodies in the central nervous system. We report here a patient with GAD autoimmunity and type 1A diabetes who developed cognitive impairment without known anti-GAD-related neurological conditions.A 73-year-old, right-handed, high school-educated Japanese housewife developed polydipsia, polyuria, progressive weight loss, and i