Distinguishing vascular inflammation and dysfunction in COVID-19
Vascular disease has many distinct phenotypes and associated functional abnormalities. While systemic conditions, ranging from metabolic to inflammatory and degenerative diseases often determine the location and make-up of accompanying vascular abnormalities, some conditions display a predominant vascular phenotype.
A discussion of vascular disease should distinguish causal, pathological, structural and functional elements. The term “vasculopathy” represents any abnormality within a blood vessel- small, medium and large caliber, veins or arteries (reviewed in Seshan) [85]. Degenerative, metabolic and inflammatory conditions, embolic diseases and coagulation disorders are responsible for acute, subacute or chronic endothelial cell injury. In many cases, non-inflammatory (necrotizing) vascular injury causes accumulation of immune complexes within the vessel’s wall. A thickened intima with immunoglobulin and complement deposition, without inflammatory lymphocyte infiltration or atherosclerotic change are typical features of an autoimmune vasculopathy [86].
The pathological features are distinct and include endothelial cell swelling, vessel wall fragmentation, vessel wall fragmentation, endothelial cell pyknosis and karyorrhexis. Pyknosis is the irreversible condensation of chromatin in the nucleus of a cell undergoing necrosis or apoptosis. Karyorrhexis, or fragmentation of the nucleus can follow if injury is severe or sustained.
Vasculitis displays classic histological findings of predominantly neutrophilic infiltrates affecting small and medium-sized blood vessels. Large vessel vasculitis occurs in some cases. Fibrinoid deposits, endothelial edema, and extravasation of red blood cells are common. A mixed inflammatory infiltrate occurs, particularly in subacute stages older lesions. The functional and phenotypic heterogeneity of the vascular endothelial lining, which is the primary target of injury, dictates different types of vascular lesions in the various organs, variability in clinical presentation, prognosis and therapy [85].