Skin microvascular changes and immunohistochemical assessment for C5b-9 and MXA staining post-eculizumab. A. Skin histology post-eculizumab. Subsequent to receiving Eculizumab, the patient underwent 6 sequential biopsies 2 weeks to 25 months after commencing the drug. In none of the post-eculizumab biopsies is there evidence of active endothelial cell injury and vascular thrombosis. A common finding in all of the biopsies is one reflective of antecedent episodes of microvascular injury characterized by subepidemal fibrosis with vascular drop out, vascular basement membrane zone duplication and vascular ectasia (diaminobenzidene, 200x). B. Inflammatory cell infiltrate in skin biopsy post-eculizumab. A variable inflammatory cell infiltrate comprising lymphocytes and histiocytes primarily arranged around blood vessels is present in all of the biopsies. The biopsy procured in March 2011, 16 months after the commencement of eculizumab, shows a striking lymphocytic and histiocytic infiltrate with abundant mucin deposition. Despite the exuberant inflammation, active microvascular injury is not seen. In particular discernible vascular thrombosis is not observed (hematoxylin and eosin, 400x). C. MxA in skin biopsy post-eculizumab. In all post-Eculizumab biopsies, there continues to be prominent expression of MxA in the epidermis, inflammatory cells and endothelium (diaminobenzidene, 1000x). D. C5b-9 in skin biopsy post-eculizumab. Nine months after the commencement of the drug, C5b-9 was no longer apparent (diaminobenzidene, 400x).