Focal brain lesions (FBL) in HIV/AIDS frequently pose a diagnostic dilemma as the etiology varies from infective (tuberculoma, toxoplasmosis and tuberculous abscesses) to neoplastic lesions like lymphoma. For determining etiology, advanced neuroimaging techniques, serological and molecular biological tests have been evolved with varying sensitivities/specificities. Stereotactic biopsy (STB) of the lesions is reserved for lesions unresponsive to appropriate therapy.
In this study, the diagnostic yield of neuroimaging [cranial CT (n=25), MRI (n=24), and Th201/99Tc SPECT scan (n=18)] is compared with histopathological diagnosis obtained by STB (n=21) or autopsy (n=4) in 25 HIV-1 subtype C seropositive individuals with FBL identified by neuroimaging with special reference to cerebral toxoplasmosis in an eighteen month study period (2006-2007).
Cerebral toxoplasmosis was the most frequent cause of FBL (21/25, 84%), followed by one case each of tuberculoma, progressive multifocal leukoencephalopathy (PML), primary central nervous system lymphoma (PCNSL) and measles inclusion body encephalitis (MIBE), the last two diagnosed at autopsy. Of the 21 cases of cerebral toxoplasmosis, definitive diagnosis with histopathological confirmation was available in 14/21 (66.6%), with indirect evidence suggesting probable toxoplasmosis in seven, all of whom responded to antitoxoplasma therapy. CT and MRI had comparable specificities (75%), while MRI had marginally higher sensitivity (85% versus 80.9%) in detecting multiple lesions. The positive predictive value of both CT and MRI was identical (94.4%), suggesting that CT maybe a cost effective screening tool in resource restricted settings, for evaluating FBL. Sensitivity of 99Tc SPECT scan for diagnosing inflammatory lesions was 75% but failed to differentiate PCNSL from toxoplasmosis. This study is the first of its kind from India analyzing FBL with specific focus on cerebral toxoplasmosis in the setting of HIV-1 subtype C.