Although characteristically a disease of multiple discrete mononeuropathies, the syndrome associated with polyarteritis nodosa may appear more or less generalized and symmetrical as a result of the accumulation of many small nerve infarctions; that is, it can simulate a polyneuropathy. In these cases, careful clinical and electrophysiologic examinations disclose elements of mononeuritis that have been engrafted on an otherwise generalized process. For example, an asymmetrical footor wrist-drop or a disproportionate affection of one nerve in a limb, such as ulnar palsy with relative sparing of function of the adjacent median nerve, are clues to the multifocal nature of the process. As often it takes form of random infarctions of two or more individual nerves. The onset is usually abrupt with symptoms of pain or numbness at a focal site along a nerve or in the distal distribution of an affected nerve, followed in hours or days by motor or sensory loss in the distribution of that nerve and then by involvement in a saltatory fashion of other peripheral nerves. Both the spinal and cranial nerves may be affected but far less often than the nerves in the limbs. Virtually no two cases are identical.
The CSF is usually normal. Nerve biopsy, usually taken from the sural nerve, will in most cases show the necrotizing arteritis in medium-size vessels (fibrinoid necrosis of all 3 coats of the vessel walls), with infiltrating eosinophils and occlusion of vessels. Muscle biopsy may also show perivascular inflammation and necrosis, but the diagnostic yield is less than for biopsy of a nerve, particularly if a sample is taken from a clinically affected nerve. On the basis of the smaller size of affected vessels and the presence of perinuclear antinuclear cytoplasmic autoantibodies (p-ANCA), Lhote and colleagues have differentiated a “microscopic” polyarteritis. Rapidly progressive glomerulonephritis and lung hemorrhage are the additional features of the latter disease, neuropathy occurring somewhat less frequently than in typical polyarteritis.
Treatment Based on the response to the systemic vasculitides with ANCA activity, mononeuritis multiplex caused by vasculitis has been treated with corticosteroids and either rituximab 375 mg/m2 weekly for 4 weeks, or cyclophosphamide 1 g/m2 intravenously once a month for several months, but other equivalent regimens have been suggested. For the corticosteroid regimen, we have used intravenous methylprednisolone, 1.5 mg/kg, for several days, followed by oral corticosteroid treatment. It appears from clinical experience that corticosteroids alone are often inadequate, but some clinicians have taken this approach initially. Azathioprine is a reasonable alternative if cyclophosphamide is not tolerated. Treatment usually must be continued for at least several months. In intractable cases and in those with systemic involvement, treatment with methotrexate may be indicated, or this may be used initially. Spontaneous remission and therapeutic arrest are known, but many cases have a fatal outcome from kidney and systemic complications. The infarctive nerve palsies and sensory loss of the mononeuropathies generally persist to a large degree even when the systemic disease is brought under control.
Eosinophilic Granulomatosis With Polyangiitis (Churg-Strauss, Allergic Granulomatosis) and Hypereosinophilic Syndrome