A 65-year-old woman is brought to the emergency department due to abnormal behavior. The patient was in her usual state of health until 3 hours ago, when she suddenly became confused and kept asking repetitive questions. She has had no headache, abnormal motor activity, or focal weakness or numbness. Medical history is significant for hypertension and migraine. Blood pressure is 136/84 mm Hg and pulse is 80/min. On physical examination, the patient is awake and alert but keeps asking, "What happened?" She can state her date of birth and address correctly, recognizes her family members, and is aware of current events. The patient recalls 0 of 3 objects after several minutes and cannot retain the physician's name despite many repetitions. Speech is fluent without dysarthria or aphasia. Cranial nerve examination shows no abnormalities. Motor strength, reflexes, and sensation are normal throughout. Blood cell count and serum chemistry panel are within normal limits. Urine drug screen is negative. CT scan of the head shows no hemorrhage. Two hours later, the patient spontaneously returns to normal. Temporary dysfunction of which of the following neural structures best explains this patient's symptoms?
This patient's sudden-onset confusion, memory loss, and anterograde amnesia (ie, inability to form new memories) resolving within 2 hours is consistent with transient global amnesia (TGA). The inability to retain new information during a TGA episode frequently causes patients to ask repetitive questions. In addition to prominent anterograde amnesia, patients with TGA have varying degrees of retrograde amnesia (ie, lack of recall of information prior to the episode). They remain fully alert and oriented to self but are typically disoriented to place. Other cognitive functions remain intact during the episode, and neurologic examination is normal. Episodes are self-limited, and amnestic symptoms resolve fully (except for events that occurred during the TGA episode itself) within 24 hours by definition.
Risk factors for TGA in this patient include older age and history of migraine. Although the specific etiology of TGA is uncertain, the clinical symptoms and neuroimaging studies implicate dysfunction of the hippocampus, the area of the brain critical for formation of new memories.
(Choice A) The arcuate fasciculus is an association fiber tract connecting Broca area and Wernicke area in the brain. Dysfunction in this tract correlates with conduction aphasia. Language comprehension and speech are normal in TGA.
(Choice C) The nucleus accumbens is part of the basal ganglia. It mediates reward and pleasure and plays an important role in addiction.
(Choice D) The piriform cortex is the brain region associated with processing olfactory information.
(Choice E) The pontine reticular formation is located in the brainstem and regulates arousal, attention, sleep, and muscle tone. Dysfunction in this area is associated with delirium, which is characterized by fluctuating levels of arousal. Patients with TGA are alert and have a relatively isolated deficit of anterograde amnesia.
Educational objective:
Transient global amnesia is a self-limited syndrome characterized by the sudden onset of prominent anterograde amnesia accompanied by repetitive questioning. Symptoms correlate with transient dysfunction of the hippocampus, the brain area responsible for the formation of new memories.