Abstract
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Objectives: Bone marrow biopsy is typically used for diagnosis as well as assessment of treatment in AML but it cannot identify extramedullary involvement. Extra medullary disease (EMD) can occur before diagnosis of AML, during treatment, or present as relapse, post chemotherapy/transplant. Conventional imaging such as CT (computed tomography) & MRI(magnetic resonance imaging), help detect additional lesions over clinical examination, but cannot detect small occult sites. PET/CT by combining metabolism with anatomy, should help detect such sites. Therefore we used PET&CT to evaluate both metabolism & structure to identify the sites of extramedullary involvement while simultaneously evaluating the intramedullary disease. Materials and Methods: A total of 22 AML patients with clinically detected EMD were prospectively evaluated with 18F-FDG PET/CT for primary staging & disease extent. After fasting for 6 hours, they were injected with 5-10 MBq/kg IV F18 FDG(Fluorodeoxyglucose) & whole body PET/CT was obtained 40-60min after injection. The scans were analyzed by 2 experienced nuclear medicine physicians & all the lesions were documented.Acquired images were evaluated by two experienced nuclear medicine physicians. SUVmax of all the identified lesions was measured & compared using SUVmax of the liver as background.
Results: A total of 22 patients (18 males, 4 females), (Mean age -9.64years (SD 4.82)) among which 19 were diagnosed with AML for the first time (mean age -9.58years (SD 4.97)) & 3 were known cases of relapse (mean age -10.00(SD 4.58)) were included. Male to female ratio of newly diagnosed cases of AML was 3:16, where as in relapse cases it was 1:2. On baseline examination 17 of the 22 patients presented with orbital protrusion & 1 each with swelling of the jaw, cheek swelling, paraparesis, urinary retention & low back ache , swelling in breast. PET/CT detected a total of 125 lesions in 22 patients, of which 28 lesions were primary lesions that were clinically detected. PET/CT thus identified additional 97 lesions. The maximum number of extramedullary lesions detected were of the lymph nodal group (n=41) ,orbital lesions (n=25), soft tissue masses and thickenings in paravertebral (n=8),presacral(n=6) prevertebral(n=2), pleural thickening (n=3) muscle deposits(n=6) spleen involvement(n=6) ,skeletal lesions (n=5) ,sinus involvement (n=5) 2 lesions each in sacral canal, buccal space, parotid region, and intra-spinal region (n=8) and 1 lesion each in lung, retrovesicular, liver, external auditory region, breast, infra-temporal, obturator region, brain, crura and pterygopalatine region (n=10). CT detected only 78 of the total 125 lesions. Infact, the mean number of lesions detected by PET per patient was significantly higher than by CT (6 and 4 respectively; p<0.001). However, same proportion of unifocal vs multifocal disease was detected by both (Unifocal disease 31.8% (7/22) patients). Median and mean TBR (median 4.58;p <0.001) in relapse patients was found to be significantly higher than that in AML patients with first diagnosis ( Although, the median values of size, SUVmax, SUVavg, & MTV were higher in relapse cases in comparison to newly diagnosed cases of AML but the difference was not statistically significant). Total MTV in patients with new diagnosis at recruitment was lower (mean: 44.49, median: 21.83 range:21.40-181.32) than relapse at recruitment (mean: 74.85median: 42.49, range:0.00-133.88), but not significantly higher(p>0.05).
Conclusions: There is significant extramedullary disease in AML patients which is missed by clinical examination as well as conventional modalities like CT. PET combined with CT (PET/CT) is a highly sensitive imaging modality in the diagnostic evaluation and detection of additional extramedullary sites.