Immune reconstitution inflammatory syndrome represents a spectrum of clinicopathologic entities encountered in human immunodeficiency virus/infected patients who have received highly active anti-retroviral therapy. The diagnosis is often challenging, treatment options are limited, and the prognosis is variable. To increase awareness and define the clinicopathologic features, we present our experience with 6 probable cases involving the brain, including 1 autopsy. Clinicopathologic review was

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... plemented by immunohistochemical analysis. There were 5 men and 1 woman, ranging in age from 34 to 47 (mean, 41; SD, 5.39) years. All patients experienced neurologic deterioration (focal deficits in 5/6) after highly active anti-retroviral therapy. All specimens showed a predominance of CD8 + lymphocytic inflammation. Concurrent CNS infections included human immunodeficiency virus encephalitis, progressive multifocal leukoencephalopathy, cryptococcal meningitis, and syphilis. One patient died, 1 was lost to follow-up, 2 improved, and 2 showed no substantial clinical changes. Subtle and overlapping features may preclude a definitive diagnosis. To capture all suspected cases, it is important to consider the possibility of this entity. In this study, the degree of CD8 + inflammation was more pronounced in the single fatal example, and mast cells were not identified in the infiltrates. Although nonspecific, imaging findings may offer clues to early diagnosis.