The mean serum IFN - γ levels of patients with erythroderma (13.80 ± 8.51 pg / mL), the plaque-type psoriatic patients (9.76 ± 5.84 pg / mL) and patients with psoriatic arthritis (10.86 ± 5.79 pg / mL) were significantly differerent from those of healthy subjects (p < 0.001).