La crosse virus encephalitis preceding neurosarcoidosis diagnosed by brain biopsy.

Childhood neurosarcoidosis is rare, and its etiology is unknown. La Crosse virus is one of the most common causes of encephalitis in North America. We report the case of a 12-year-old boy who had La Crosse virus encephalitis and subsequently developed imaging and pathologic findings suggestive of neurosarcoidosis. He presented with acute onset of transient aphasia 4 months after an episode of encephalitis; serology results at the time of aphasia were positive for La Crosse virus. Brain MRI revealed diffuse subcortical nodular lesions. His serum angiotensin-converting enzyme level was elevated, and brain biopsy revealed noncaseating granuloma. It is interesting to note that he has had no recurrence of aphasia; repeat MRI showed significant improvement of nodular lesions without therapy. To our knowledge, this is the first case of La Crosse virus encephalitis associated with neurosarcoid findings.