In addition to diabetes, several systemic conditions are accompanied by acute or subacute involvement of multiple individual nerves serially or almost simultaneously. This configuration gives rise to the distinctive clinical picture of mononeuropathy, or mononeuritis multiplex. The most notable examples are associated with vasculitides that produce nerve infarction, the archetype being polyarteritis nodosa and other vasculitides and particularly a form of idiopathic vasculitis that is confined to the peripheral nervous system. The distinctive features of the multiple mononeuropathy syndromes are the acute or subacute evolution of complete or almost complete sensorimotor paralysis in the distribution of single peripheral nerves. In addition to vasculitis or the nerves, sarcoidosis, forms of HIV-related neuropathy, Leprosy and Lyme disease may become manifest in this fashion, probably from infiltration or inflammation of nerves rather than infarction. The diabetic mononeuropathies were addressed in the preceding section.
More than half of all cases of mononeuropathy multiplex can be traced to a systemic vasculitis involving the vasa nervorum. These are the main causes of mononeuritis multiplex. Included in this category are polyarteritis nodosa, the eosinophilic granulomatosis with polyangiitis (formerly called Churg-Strauss syndrome of allergic bronchial asthma and eosinophilia), rheumatoid arthritis, lupus erythematosus, scleroderma, cryoglobulinemia, granulomatosis with polyangiitis, and the aforementioned idiopathic variety of vasculitis that is confined to the peripheral nerves and has no systemic manifestations. In Said’s series of 425 cases of vasculitis (2005) affecting the peripheral nerves, 24 percent were associated with polyarteritis nodosa, 23 percent with rheumatoid arthritis, and about 32 percent with other connective tissue diseases; in 21 percent there were no signs of vasculitis beyond the peripheral nerves. Elevation of the sedimentation rate, C-reactive protein and other serologic abnormalities are typical features but not invariable of this group. The most recent addition to the diagnostic list has been a microscopic polyangiitis that is different from the vasculitis of medium-sized vessels that characterizes the remainder of the group. This subject has been reviewed by Collins, who summarizes guidelines for diagnosis.
Almost 75 percent of cases of polyarteritis nodosa include involvement of the small nutrient arteries of peripheral nerves (these figures come from autopsy series), but a symptomatic form of neuropathy develops in about half this number. Nevertheless, involvement of the peripheral nerves may be the principal or first sign of the disorder, before the main systemic components of the clinical picture—abdominal pain, hematuria, fever, eosinophilia, hypertension, vague limb pains, and asthma—have not fully declared themselves or have been misinterpreted.