SPECT thallium-201 combined with Toxoplasma serology for the presumptive diagnosis of focal central nervous system mass lesions in patients with AIDS

Objective: To determine the utility of brain thallium-201 single photon emi ssion computerized tomography (TI-201 SPECT) combined with Toxoplasma serol ogy for the diagnosis of focal CNS lesions in patients with AIDS. Methods: Sixty-one consecutive HIV-infected patients with focal CNS lesion( s) on head computed tomography (CT) or MRI scan who underwent brain TI-201 SPECT and serum Toxoplasma serology were evaluated, retrospectively Thalliu m-201 uptake ratios were calculated by comparing lesion activity to contral ateral scalp activity. Diagnoses were made by a combination of histology, s erology, PCR, and empirical response to therapy. Toxoplasma serologies (IgG IFA) were compared in the patients with central nervous system (CNS) toxop lasmosis and those without CNS toxoplasmosis, Results: Fifty-six patients w ere evaluable and a definitive diagnosis was made in 38 patients: toxoplasm osis (17), lymphoma (14), PML (three), Aspergillus (one), tuberculoma (one) , Cryptococcus (one), varicella-zoster virus (one), Patients with lymphoma had significantly higher lesion/contralateral scalp ratios compared to pati ents without lymphoma: 1.03 vs. 0.67, P < 0.05. Using a cut-off of 0.90 for the lesion/scalp uptake ratios (based on analysis of ROC curves) the sensi tivity and specificity for the diagnosis of lymphoma were 86% and 83% respe ctively Serum Toxoplasma IgG titres were significantly higher in patients d iagnosed with toxoplasmosis compared to those with a diagnosis other than t oxoplasmosis, 1:5444 vs. 1:15, P < 0.05, Only. one patient with confirmed t oxoplasmosis had a Toxoplasma serology < 1:256, while no patients without t oxoplasmosis (including all lymphoma patients) had serologies > 1:256. Conclusions: In a series of HIV-infected patients, TI-201 SPECT was able to accurately differentiate primary brain lymphoma from other causes of focal CNS lesions in most patients; however, both false positive and false negat ive results occurred. By combining TI-201 SPECT with serum Toxoplasma IgG, diagnostic accuracy was improved. (C) 2000 The British Infection Society.