Purpose: To evaluate the diagnostic specificity of thallium and gallium scan mismatch as a sign of mycobacterial infection in immunodeficient patients.
Materials and methods: Thallium and gallium scans obtained in 56 immunodeficient patients between January 1989 and March 1994 were retrospectively reviewed, with special attention to the final diagnoses in all patients with thallium-gallium scan mismatch compared with those whose scans showed other scintigraphic patterns.
Results: Fourteen patients had focal gallium uptake, but no thallium uptake, in the mediastinum and hilar nodes (thallium-gallium mismatch). Twelve of the 14 had culture-proved mycobacterial infections; one had cryptococcal infection; and in one, the diagnosis was not established. Thirty-seven of the remaining 42 patients who had different scintigraphic patterns on thallium-gallium scans had other complications of acquired immunodeficiency syndrome such as Kaposi sarcoma, non-Hodgkin lymphoma, and bacterial pneumonia. The diagnosis in five of the 42 patients was not known because follow-up data were incomplete.
Conclusion: The thallium-gallium mismatch pattern in immunodeficient patients is specific for mycobacterial infection.