Nonsystemic vasculitic neuropathy: update on diagnosis, classification, pathogenesis, and treatment

The primary systemic vasculitides are autoimmune disorders characterized by chronic immune responses directed against vascular structures. They commonly affect small or medium-sized vessels in the peripheral nervous system (PNS), producing vasculitic neuropathies. Some patients develop vasculitis clinically restricted to the PNS, known as nonsystemic vasculitic neuropathy (NSVN), the most commonly encountered vasculitic neuropathy in pathologically based series. Diabetic and nondiabetic radiculoplexus neuropathies are clinical variants of NSVN. NSVN is clinically similar to systemic vasculitis-associated neuropathies except for reduced severity. Patients most commonly present with progressive, stepwise pain, weakness, and numbness over multiple months. Almost all exhibit a multifocal or asymmetric, distally accentuated pattern of involvement. The most commonly affected nerves are the common peroneal nerve in the leg and the ulnar nerve in the arm. Sedimentation rate is mildly to moderately elevated in 50%; other markers of systemic inflammation are generally normal. Electrodiagnostic studies reveal a predominantly axonal, asymmetric, sensorimotor polyneuropathy, but pseudo-conduction blocks may occur. Definite diagnosis requires biopsy evidence of vascular inflammation and signs of active or remote vascular damage. In biopsies lacking definite vasculitis, the diagnosis is suspected if axonal alterations are accompanied by perivascular inflammation and such supportive features as Wallerian-like degeneration, asymmetric fiber loss, hemosiderin, vascular immune deposits, neovascularization, myofiber necrosis/regeneration, focal perineurial damage, and endoneurial purpura. NSVN preferentially affects larger epineurial arterioles. Epineurial infiltrates are composed primarily of T cells and macrophages, suggesting that cellular cytotoxicity is the primary effector mechanism. Systemic vasculitides with progressive neuropathy are usually treated with cyclophosphamide and prednisone. No randomized controlled trial of therapy has been performed in NSVN, but data from retrospective cohorts suggest that combination therapy is more effective than steroid monotherapy. Once remission has been induced, cyclophosphamide should be replaced with azathioprine or methotrexate. Refractory patients can be treated with intravenous immunoglobulin, mycophenolate, rituximab, infliximab, or alemtuzumab. Although long-term outcome is reasonably good, more than one third of patients relapse, infrequent patients die from the disease or its treatment, and still others develop chronic pain.