Background: 18F-FDG PET is a promising technique in sarcoidosis imaging, although it is not incorporated in routine activity assessment. The purpose of this study was to correlate 18F-FDG PET with standard sarcoidosis activity parameters during infliximab treatment.
Methods: Twelve patients with refractory sarcoidosis were treated with 6 cycles of infliximab. Pre- and post-therapy 18F-FDG PET was visually evaluated and SUVmax was measured. In addition, the effect of infliximab was evaluated by changes in symptoms, angiotensin converting enzyme (ACE), soluble interleukin-2 receptor (sIL-2R), vital capacity (VC), diffusion capacity of the lung for carbon monoxide (DLCO) and chest radiography. SUVmax and conventional parameters were correlated.
Results: Clinical improvement as judged by conventional parameters was seen in all patients, though with a minor response in one. Symptoms improved in 11/12 patients while chest radiographic stages did not change. The decrease in ACE was 39% and in sIL-2R 47% (p<0.01). Improvement of VC and DLCO was 5.4% and 3.3% (p<0.05), respectively. 18F-FDG PET revealed either improvement or normalization in 11/12 (92%) clinically responding patients. The overall decrease in SUVmax was 55% (p<0.01); the patient with a limited response showed a 34% increase. A decrease in SUVmax of the lung parenchyma correlated with an improvement of VC (r=-0.75, p<0.01). No significant correlation between SUVmax and other parameters was found.
Conclusion: Changes imaged by 18F-FDG PET during infliximab treatment in sarcoidosis patients correlate with signs of clinical improvement to a considerate extent, which supports the hypothesis that 18F-FDG uptake represents disease activity.