Ultrastructure of the Arthus Phenomenon in muscle.

Specific blood-tissue barrier alterations were observed in a 2-year-old boy with a myopathic lesion in his muscle. Close by, degenerative changes were present in muscle fibers, three types of vascular abnormalities, i.e. increased vascular permeability, neutrophil aggregation, and damage of endothelium with thrombi formation, suggest that a process of vasculitis took place in the muscle of this patient. On the basis of current information it is not entirely clear whether this Arthus-like reaction observed in the primarily affected muscle represents a widespread vascular bed defect or whether it is the consequence of an additional secondary symptom possibly dependent upon muscle necrosis.