Isolated vasculitis of the peripheral nervous system.

Vasculitis restricted to the peripheral nervous system (PNS), referred to as nonsystemic vasculitic neuropathy (NSVN), has been described in many reports since 1985 but remains a poorly understood and perhaps under-recognized condition. There are no uniform diagnostic criteria. Classification is complicated by the occurrence of vasculitic neuropathies in many systemic vasculitides affecting small-to-medium-sized vessels and such clinical variants as nonsystemic skin/nerve vasculitis and diabetic/non-diabetic lumbosacral radiculoplexus neuropathy. Most patients present with painful, stepwise progressive, distal-predominant, asymmetric or multifocal, sensory-motor deficits evolving over months-to-years. NSVN is identical to but less severe than systemic vasculitis-associated neuropathies (SVNs). All vasculitic neuropathies are axonal by electrodiagnostic/pathologic criteria. Laboratory testing is unremarkable except for mildly elevated erythrocyte sedimentation rate (ESR) in 50%. Highly elevated ESRs, leukocytosis, rheumatoid factors, and anti-neutrophil cytoplasmic antibodies (ANCAs) raise concern for underlying systemic vasculitis. Without a specific clinical/laboratory marker, the condition depends on nerve biopsy for diagnosis. Biopsies showing necrotizing vasculitis are about 50% sensitive, mandating reliance on "suspicious" changes in many patients. Vasculitic lesions predominate in smaller epineurial vessels and are milder than those in SVNs. The disorder is often accompanied by subclinical involvement of adjacent muscles and skin. NSVN has the potential to spontaneously relapse and remit but neurologic deficits accumulate. No randomized controlled trials have been performed, but one retrospective cohort survey showed combination therapy to be more effective than prednisone alone. Although most patients have a good outcome, more than 30% relapse and 60% have residual pain. Many nosologic, pathogenic, diagnostic, and therapeutic questions remain unanswered.