A 21-year-old man presented in a state of delirium with compulsive, pathologic laughter and no focal neurologic findings. Brain imaging revealed a lenticulostriate artery infarct of the caudate nucleus. The absence of neurological signs made the diagnosis difficult, but the presence of delirium was a clue to the existence of structural brain disease.
Keywords: MRI scan; brain imaging; caudate nucleus infarct; compulsive laughter; delirium; encephalopathy; focal neurological examination; impaired cognition; lenticulostriate artery infarct.