Thymic lesions in patients with myasthenia gravis: Characterization with thallium 201 scintigraphy

PURPOSE: To assess thallium 201 (Tl-201) single photon emission computed to mography (SPECT) for evaluation of thymic lesions associated with myastheni a gravis (MG), including lymphoid follicular hyperplasia (LFH) and thymoma. MATERIALS AND METHODS: Tl-201 SPECT and computed tomography (CT) were perfo rmed preoperatively in 46 patients with MG who had undergone thymectomy. SP ECT was conducted 15 (early image) and 180 (delayed image) minutes after Tl -201 injection. Results were visually assessed, and Tl-201 uptake ratios (t hymic lesion count density/lung count density) were measured for quantitati ve analysis. Uptake was analyzed among the normal thymus, LFH, and thymoma patient groups. RESULTS: Histopathologic results indicated a normal thymus, LFH, and thymom a in 19, 16, and I I patients, respectively. Mean uptake ratios in the norm al thymus, LFH, and thymoma were 0.96 (95% CI: 0.90, 1.03), 1.14 (95% CI: 1 .04, 1.25), and 1.87 (95% CI: 1.56, 2.25), respectively, on early images an d 1.09 (95% CI: 1.00, 1.18), 1.65 (95% CI: 1.48, 1.85), and 2.03 (95% Cl: 1 .65, 2.50), respectively, on delayed images. Thymoma showed more intense Tl -201 accumulation than did the normal thymus (P < .001) and LFH (P <.001) o n early images. Both thymoma (P <.001) and LFH (P <.001) displayed more int ense uptake than did the normal thymus on delayed images. CONCLUSION : Tl-201 SPECT can enable differentiation between normal thymus, LFH, and thymoma in patients with MG.