18F-FDG PET in sarcoidosis: an observational study in 12 patients treated with infliximab

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.

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.

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.

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.