A case of hypocomplementemic urticarial vasculitis syndrome complicated by eosinophilic pneumonia: a case report and review of the literature.

The primary symptom of urticarial vasculitis (UV), which is a histopathological leukocytoclastic vasculitis disease, is an eruption that resembles urticaria. Other organs may also experience accompanying symptoms. Lung lesions with UV are mostly obstructive pulmonary disease with smoking. However, the coexistence of eosinophilic pneumonia (EP) and complicated UV remains unclear. We report a man in his 70s with chronic obstructive pulmonary disease who attended our department with ring-shaped erythema, marginal edema, and pigmentation. Additionally, a skin histological analysis showed nuclear dust and perivascular neutrophil infiltration, while a blood sample showed a decrease in C3 and C1q concentrations. Administration of prednisone temporarily improved the eruption. However, he developed a cough and a new UV eruption 1 year later. Computed tomography revealed infiltration in the right upper lobe of the lungs, and a blood sample showed a high eosinophil count. He was finally diagnosed with hypocomplementemic urticarial vasculitis syndrome and idiopathic chronic EP. A previous study showed that serum C1q concentrations in patients with EP were lower when this disease was active. Whether a decline in C1q concentrations can cause EP is unclear. However, our case is unique owing to the co-onset of EP with low complement concentrations and recurrence of UV.