^{PET-PASI score: Utility of FDG-PET/CT in Psoriasis}

Purpose: 1) to investigate the metabolic activity of the psoriatic skin lesions with FDG-PET/CT imaging and 2) to correlate FDG-PET findings with Psoriasis Area and Severity Index (PASI) scores, the most widely-used grading system for psoriasis.

Methods: A subset of 33 subjects from a single center from a prospective multi-center clinical trial [NCT01553058] with moderate-to-severe psoriasis were included. Patients underwent whole-body FDG-PET/CT imaging 120 min after intravenous FDG. Each patient was graded by our ‘PET-PASI’ scoring system, a qualitative review of multi-plane reconstructions for both attenuation corrected (AC) and non-attenuation corrected (NAC) PET images. Each patients’ body was divided into four areas (head, arms, trunk, legs) and body involvement was scored from 0 (no involvement) to 6 (maximal involvement) corresponding to the percent of affected skin. The FDG uptake score was multiplied by body involvement and a scaling factor for the respective region (0.1 for head, 0.2 for arms, 0.3 for trunk 0.4 for legs), yielding the PET-PASI score. PASI and PET-PASI scores were correlated using Spearman’s rho analysis.

Results: Our study demonstrated a moderate but statistically significant positive correlation between each patient’s corresponding PET-PASI and PASI scores (r=0.53, p<0.001). We also found positive correlations between PASI and PET-PASI component scores in four body regions (head and neck: r=0.22, trunk: r=0.48, upper limbs: r=0.26 and lower limbs: r=0.58).

Conclusions: NAC images are easier to detect lesions such as superficial lymphoma and melanoma compared to AC scans. As such, AC and NAC FDG-PET/CT images may be utilized to evaluate lesions in patients with moderate-to-severe psoriasis. Our methodology could have future implications in diagnosis and therapeutic management of psoriasis.