Ultrastructure of the microvessels in skeletal muscle in a case of systemic capillary leak syndrome.

The microvessels of skeletal muscle were examined electron microscopically in a case of systemic capillary leak syndrome (SCLS). One biopsy was taken in a free interval of the disease and one about 6 hours after the onset of an attack with hypovolemia. The microvascular endothelium exhibited a large number of multivesicular bodies, especially in the specimen obtained during an attack. Possibly this indicates a high heterophagic activity of the endothelium. A blebbing of the luminal surface of arteriolar endothelium was observed in the attack specimen. Since a complement activation seemed to occur during attacks, the blebbing is tentatively interpreted as a sign of a complement-mediated injury to the endothelium, leading to a breakdown of the endothelial barrier. This mechanism might explain the dramatic increase of microvascular permeability to plasma proteins during an attack of SCLS. The findings did not indicate that the increase might depend on some disturbance of the transendothelial vesicular transport function, nor could any openings of endothelial junctions, as in inflammation, be demonstrated. Regionally the periendothelial basal lamina appeared thickened, a finding which seems common in angiopathies of different kinds.