The Papez circuit is a conglomerate of neuronal pathways involved in the control of memory and emotion. This network involves an eloquent interplay between the hippocampus and neighboring structures, including the thalamus. We describe a case of sudden onset anterograde amnesia after an infarction to the anterior thalamus. 

A 64-year-old educated Trinidadian woman with no known past medical history presented to the hospital brought in by her family with sudden onset cognitive impairment. Initial vitals and general physical examination were unremarkable. Neurologic examination was notable for deficits on mental status exam. She knew she was in the hospital, but was unsure why, and was unable to recall the date. Speech was fluent with intact naming and repetition, and she was able to briskly follow 3-step cross-body commands. Immediate recall of 5 words was 5/5, though delayed recall at 5 minutes was 0/5, even with category or multiple-choice cueing. Trail Making Test was prolonged. Laboratory testing including syphilis screen and nutritional studies were unremarkable. CT of the head without contrast revealed a hypodensity within the left anterior medial thalamus with corresponding diffusion restriction on MRI. Throughout her hospital stay, she did not recognize nursing staff nor her physicians. Each visit played like her first visit to the hospital, as she repeatedly could not state why she was in the hospital nor what had afflicted her despite recurrent explanations. Echocardiogram revealed severe mitral stenosis concerning for a rheumatic heart valve, for which she was placed on coumadin for secondary stroke prevention.

An infarct involving the anterior thalamus in isolation can present with cognitive deficits, particularly anterograde amnesia. This case highlights the thalamus’s contribution to memory processing and emphasizes how history and a detailed mental status examination should not be overlooked in the evaluation of patient with sudden onset neurologic symptoms.