Unique amnestic syndrome after isolated left anterolateral thalamic stroke: a case report

The thalamus plays a key role in motor and sensory processes of the brain. Though thalamic stroke is among the less frequent, even a minimal lesion can result in a serious impairment and long-lasting disability. After thalamic stroke, cases of dysexecutive syndrome and so-called diencephalic amnesia have been observed, yet the precise characterisation or categorisation of such amnestic syndrome is not available. Pure amnesia can be the one and only indication of a thalamic lesion. We present a unique case of a patient after left anterolateral thalamic stroke suffering from isolated severe amnesia and disorientation. We conducted extensive neuropsychological testing of the patient's memory and discovered contrasting results in different aspects of memory.

A 75-year-old woman was admitted for neurological rehabilitation two weeks after being diagnosed with acute left anterolateral thalamic ischemic stroke. The initial symptoms with which she presented in the emergency room were acute confusion, disorientation and memory impairment; apart from that, the patient did not have any other neurologic signs. As observed on the MRI, the lesion was restricted mostly to the left anterior nucleus without affecting the mammillothalamic tract. The neuropsychological testing revealed anterograde episodic memory loss with preserved visual recognition and auditive short term memory; inability to freely recall semantic information, spatial and time disorientation, apathy and significantly reduced intrinsic and phasic attention, and immediate and delayed prose recall deficiency.

The knowledge that memory impairment and disorientation can be the only symptoms of the stroke is a crucial piece of information, which is needed to be able to make a decision about proper treatment. Abstention from immediate intervention often leads to irreparable memory deficit for the rest of the patient's life. The results of neuropsychological testing show the essential role of AN in creating episodic memory, in the working memory network and indicate its role as a critical interface between short-term and long-term memory. A theory explaining such a profound impairment of working and anterograde episodic memory has not yet been formulated.