Disseminated vasculomyelinopathy in the peripheral nervous system mediated by immune complexes (ICs). Immunohistochemical studies of sciatic nerves in chronic serum sickness (CHSS) in rabbits.

Histological examination of 20 sciatic nerves from rabbits with experimental chronic serum sickness (CHSS) revealed patchy vasculitis of the vasa nervorum of various intensity. The vessel lesions ranged from endothelial proliferation to vessel wall necrosis with fibrinoid degeneration and infiltration by lymphocytes, plasma cells, macrophages and, sporadically, by neutrophils. Perivascularly, there were oedema, chronic infiltrates or small haemorrhages. The myelinated fibres in close relation to the vascular system were focally depleted and features of perivascular demyelination were found. Teased fibres showed paranodal and segmental demyelination, axonal degeneration and, sporadically, remyelination. In all cases, immunofluorescent deposits of bovine serum albumin (BSA), IgG and C3 complement were found in and around some vasa nervorum. Other indirect evidence for immune complex (IC) deposition was provided by ultrastructural examination where vascular and endoneurial osmophilic deposits were found; in 4 cases with paracrystalline organization resembling cryoglobulin component. IC-mediated vasculitis led to blood-nerve barrier impairment and leakage of serum proteins into the endoneurial space. The morphological and immunohistochemical changes in this model which develop after a latency period of 2 or more weeks, strongly resemble those observed in human acquired inflammatory demyelinating polyradiculoneuropathies or in connective tissue diseases.