A small cerebral infarction in the basal ganglia causing progressive psychosis followed by dementia

A 70-year-old woman was admitted to our hospital because of an obsessive state with irritability and visual hallucination. She had suffered a mild head injury two weeks ago, but computed tomography (CT) scan of the brain showed no traumatic lesions. And acute responsive psychosis was suspected, but a low score of 8 points (full score of 30 points) on Hasegawa dementia scale (HDS -R) suggested occult cerebral lesions. Magnetic resonance imaging (MRI) revealed a new small ischemic change from the posterior limb of the left internal capsule to the tail of the left caudate nucleus by diffusion-weighted imaging, in addition to multiple old lacunar infarctions in bilateral basal ganglias in T 2-weighted imaging and fluid attenuated inversion recovery. After improvement of her mental irritability, the patient still displayed dementia with severe recent memory disturbance. Psychological analysis demonstrated vascular dementia, and her HDS -R score was only 9 points when she was discharged our hospital 6 weeks after admission. Therefore, the authors concluded that her psychosis-like reactions and severe dementia had been caused by the small infarction. We emphasize that a new small infarction may cause dementia as "multi-infarct dementia" in patients with multiple old lacunar infarctions in bilateral basal ganglias, even though the new ischemic lesions may not be anatomically associated with the mental symptoms.