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An 81-year-old man is brought to the emergency department with new-onset amnesia and dysphasia. The patient's wife reports that he has had a fever since yesterday. She also says he has complained of a headache for the past 2 days and has had difficulty finding the right words to express himself. Physical examination confirms dysphasia and amnesia and reveals significant somnolence and a left-sided facial weakness sparing the forehead. The patient is febrile to 38.9°C (102.0°F). MRI is ordered.
What finding would be expected on MRI?
A.A normal MRI, as this patient most likely is having complex partial seizures
B.A parotid tumor along the peripheral course of cranial nerve VII
C.A subdural hematoma
D.An ischemic stroke involving the territory supplied by the left medial artery
E.Enhancing lesions in the left temporal lobe with surrounding edema
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The correct answer is E. 54% chose this.
This patient's new-onset mental status changes and central facial nerve palsy with fever suggest herpes simplex virus (HSV) encephalitis, which would appear as an enhancing lesion in the left temporal lobe with surrounding edema on MRI. Typical symptoms are altered mental status and/or level of consciousness, cranial nerve deficits, hemiparesis, dysphasia, aphasia, ataxia, or focal seizures, together with fever. Central nervous system invasion is thought to occur after an episode of recurrent HSV-1 infection due to viral reactivation with subsequent spread. MRI is the preferred imaging modality for diagnosis and follow-up studies of herpes encephalitis, although early studies may be negative. A lumbar puncture would most likely reveal a lymphocytic pleocytosis, increased number of RBCs, and an elevated protein level. HSV can be detected in the cerebrospinal fluid with polymerase chain reaction analysis or culture. Suspicion for HSV should be high in patients with altered mental status and fever, as mortality is high (70%) if left untreated. Treatment is weight-based intravenous acyclovir for 14-21 days.
A is not correct. 2% chose this.
A complex partial seizure is the most common type of seizure in adults and can present similarly to absence seizures in children. Patients often seem to stare into space and either remain motionless or engage in repetitive behaviors (automatisms). The seizures typically last less than 3 minutes and are followed by a postictal phase, often characterized by somnolence, confusion, and headache for up to several hours. Fever is not part of a complex partial seizure, although complex partial seizures may be caused by HSV encephalitis.
B is not correct. 3% chose this.
A peripheral facial nerve paralysis will involve the forehead muscles. A central facial nerve paralysis spares the forehead muscles, as there is cross-innervation from the other side of the brain. Therefore this patient has a central facial nerve paralysis. In addition, his other clinical findings are unlikely to be caused by a parotid tumor alone.
C is not correct. 12% chose this.
A subdural hematoma is caused by blood in the subdural space around the brain. It is classified as either acute or chronic. Although the acute form may present with pronounced symptoms, manifestations of the chronic form may be quite subtle. Typical clinical findings are altered level of consciousness, unilateral cranial nerve III or VI deficits, and hemiparesis; papilledema due to increased intracranial pressure with associated nausea, vomiting, and increased somnolence is less common. Fever is not part of the presentation of a subdural hematoma.
D is not correct. 29% chose this.
An ischemic stroke involving the territory supplied by the left medial artery may be associated with amnesia and dysphasia or aphasia. However, hemiparesis and an altered sensorium on the contralateral side are also frequently present. Fever is unlikely in a stroke and should always suggest an infection.
Bottom Line:
HSV encephalitis may present with subtle findings and temporal lobe enhancement on MRI, and a high level of suspicion along with early treatment is crucial, especially if the patient presents with fever along with neurologic findings.
