Purpose: Studies have suggested using Tl-201 brain SPECT to differentiate lymphoma from infectious processes and to determine the timing for biopsy or empirical therapy for patients with AIDS-related brain lesions. This study prospectively investigated the utility of Tl-201 SPECT in distinguishing central nervous system lymphoma from non-neoplastic disease in patients with AIDS.
Materials and methods: Fourteen patients with AIDS and focal abnormalities on computed tomography or magnetic resonance imaging underwent brain SPECT before diagnosis (12 by biopsy, 2 by clinical course and response to therapy). A an uptake ratio (UR) was obtained by drawing a region of interest around the lesion, measuring average counts per pixel, and dividing this value by the value of a non-lesion-containing contralateral region of interest. The UR cutoff producing the highest accuracy (TP+TN/TP+TN+FP+FN) in discriminating lymphoma from another condition was determined from URs generated from these 14 patients.
Results: Five patients had lymphoma, five had toxoplasmosis, one had Herpes simplex virus encephalitis, two had progressive multifocal leukoencephalopathy, and one had gliosis (UR, 0.8). Patients were separated into categories of lymphoma or nonlymphoma. The mean UR was 2.2 +/- 1.6 (range, 1.0 to 3.85) for lymphoma and 1.7 +/- 0.8 (range, 0.7 to 3.2) for nonlymphoma. Only a UR of 1.63 resulted in sensitivity and specificity better than 50% (60% and 55%, respectively), with an accuracy of 57%, positive predictive value of 43%, and negative predictive value of 71%.
Conclusions: Tl-201 brain SPECT appears unreliable for differentiating primary lymphoma from nonmalignant brain lesions in patients with AIDS. Early brain biopsy is necessary to establish a definitive diagnosis when appropriate.