Toxoplasmosis vs. Lymphoma - Differentiation by SPECT

5/04/01 (Agahtehrani)

Question: How useful is SPECT in the differentiation of Toxoplasmosis from AIDS-related Lymphoma?

<1>

Unique Identifier: 20363315 / PubMed Identifier: 10908023

Authors: Skiest DJ. Erdman W. Chang WE. Oz OK. Ware A. Fleckenstein J.

Institution: Department of Medicine, The University of Texas, Southwestern Medical Center, Dallas 75235-9133, USA.

Abstract: OBJECTIVE: To determine the utility of brain thallium-201 single photon emission computerized tomography (Tl-201 SPECT) combined with Toxoplasma serology 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 Tl-201 SPECT and serum Toxoplasma serology were evaluated, retrospectively. Thallium-201 uptake ratios were calculated by comparing lesion activity to contralateral scalp activity. Diagnoses were made by a combination of histology, serology, PCR, and empirical response to therapy. Toxoplasma serologies (IgG IFA) were compared in the patients with central nervous system (CNS) toxoplasmosis and those without CNS toxoplasmosis. RESULTS: Fifty-six patients were evaluable and a definitive diagnosis was made in 38 patients: toxoplasmosis (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 patients 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 sensitivity and specificity for the diagnosis of lymphoma were 86% and 83%, respectively. Serum Toxoplasma IgG titres were significantly higher in patients diagnosed with toxoplasmosis compared to those with a diagnosis other than toxoplasmosis, 1:5444 vs. 1:15, P < 0.05. Only one patient with confirmed toxoplasmosis had a Toxoplasma serology < 1:256, while no patients without toxoplasmosis (including all lymphoma patients) had serologies > 1:256. CONCLUSIONS: In a series of HIV-infected patients, Tl-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 negative results occurred. By combining Tl-201 SPECT with serum Toxoplasma IgG, diagnostic accuracy was improved.

<3>

Unique Identifier: 96268142 / PubMed Identifier: 8965186

Authors: Lorberboym M. Estok L. Machac J. Germano I. Sacher M. Feldman R. Wallach F. Dorfman D.

Institution: Department of Radiology, Mount Sinai School of Medicine, New York, New York, USA.

Abstract: This study sought to assess whether 201Tl brain SPECT can significantly reduce the time required for the differential diagnosis of primary central nervous system (CNS) lymphoma and cerebral toxoplasmosis in patients with AIDS. METHODS: Eighteen patients who presented with focal lesions on CT or MRI, or both, underwent 201Tl brain SPECT shortly after admission and before a CT-guided stereotactic brain biopsy. Early and delayed 201Tl uptake ratios were obtained for patients with positive 201Tl study results, and the retention index of 201Tl was calculated. RESULTS: Ten patients had 11 foci of significantly increased 201Tl uptake in regions of corresponding CT/MRI lesions. Five of these patients had biopsy-proven lymphomas, one of them in two separate foci. Another patient was found to have metastatic adenocarcinoma. Three patients had a clinical course and response to radiation therapy consistent with lymphoma, and study results in another patient were considered falsely positive. Of nine patients with no 201Tl uptake in regions of CT/MRI lesions, two had biopsy findings consistent with a benign etiology, and the other seven improved clinically on antitoxoplasmosis medications alone. The overall sensitivity of 201Tl brain SPECT was 100%, and specificity was 90%. The 201Tl retention index in patients with lymphomas was significantly higher than that in patients with adenocarcinomas and nonmalignant lesions (1.35 +/- 0.16 versus 0.24 and 0.56, respectively). CONCLUSION: Thallium-201 brain SPECT is a sensitive and specific method for rapid differential diagnosis of CNS lymphoma and toxoplasmosis in patients with AIDS. The 201Tl retention index is useful in differentiating CNS lymphomas from other malignant and nonmalignant pathologies.

<4>

Unique Identifier: 95168131 / PubMed Identifier: 7863938

Authors: Ruiz A. Ganz WI. Post MJ. Camp A. Landy H. Mallin W. Sfakianakis GN.

Institution: Department of Diagnostic Radiology, University of Miami School of Medicine, FL 33136.

Abstract: PURPOSE: To determine whether thallium-201 brain single-photon emission CT could be used to make the distinction between central nervous system lymphoma and toxoplasma encephalitis, which may not be possible by routine MR and CT. METHODS: A total of 37 patients with acquired immunodeficiency syndrome who had intracranial mass lesions found during a 9-month prospective study by either MR or CT underwent further evaluation with Tl-201 brain single-photon emission CT. RESULTS: Twelve patients had increased intense focal Tl-201 uptake. All of these patients had either biopsy- or autopsy-proven lymphoma. Twenty-five of the patients studied had no Tl-201 brain uptake in the lesion(s); 24 of these patients had toxoplasma encephalitis on clinical follow-up. One patient with no Tl-201 uptake was found by cerebrospinal fluid analysis to have mycobacterium tuberculosis abscess. CONCLUSION: Patients with acquired immunodeficiency syndrome who have intracranial mass lesions on MR or CT may benefit from Tl-201 brain single-photon emission CT because it can help distinguish between lymphoma and infectious lesions such as toxoplasma encephalitis.