RESUMO
INTRODUCTION: The term dementia refers to the deterioration of the intellectual or cognitive functions, with little or no alteration of consciousness, which is capable of interfering with the activities of daily living and the ability to cope by oneself. One infrequent cause of dementia is its being secondary to a thalamic lesion and is normally due to the involvement of both thalami. CASE REPORT: We report a case of sudden onset dementia caused by lesions affecting only the left thalamus. A 64 year old right handed female patient with chronic arterial hypertension for which she received regular treatment. The patient visited because of difficulty in speaking without any alterations to consciousness, and amnesia of recent anterograde and retrograde events. A CAT scan of the brain revealed a superlacuna in the left thalamus. From then on, the patient presented memory disorders, the most typical being loss of retention memory. CONCLUSIONS: Thalamus injuries that are accompanied by dementia are commonly bilateral and are preferably located in the anterior and medial nuclei. There have been cases of memory disorders secondary to unilateral infarcts of the thalamus and these are related to a thalamocortical deafferentiation. Our case is one of sudden onset thalamic dementia secondary to an infarct affecting only the left thalamus.