A second group that affects the mediumand smaller-sized vessels includes polyarteritis nodosa, the Churg-Strauss type of arteritis, Wegener granulomatosis, systemic lupus erythematosus, Behçet disease, hypersensitivity angiitis, Kohlmeier-Degos disease, and the small vessel disorder of Susac syndrome. Immunologic studies show that in most of these processes there is an abnormal deposit of complement-fixing immune complex on the endothelium, leading to inflammation, vascular occlusion, or rupture with small hemorrhage. The initial inflammatory event is thought in some cases to be evoked by a virus, bacterium, or drug, but these are rarely proven in any one case. It is postulated by some immunologists that in the granulomatous arteritides, a different mechanism is operative—that an exogenous antigen induces antibodies that attach to the primary target (the vessel wall) as immune complexes, damage it, and attract lymphocytes and mononuclear cells. The giant cells form around remnants of the vessel wall. Wegener granulomatosis may fit this model. An acute necrotizing cerebral angiitis sometimes complicates ulcerative colitis and responds to treatment with prednisone and cyclophosphamide; it may also belong in this category. Mixed essential cryoglobulinemia, a vasculitic disorder that more often affects the peripheral than the central nervous system, may nonetheless produce an encephalopathy.
Another entirely different type of small vessel arteritis occurs as a hypersensitivity phenomenon. Often it is associated with an allergic skin lesion (Stevens-Johnson vasculopathy or a leukocytoclastic vasculitis). The clinical picture does not resemble that of polyarteritis nodosa, but the central or peripheral nervous system is affected in rare instances. The response to corticosteroids is excellent. The special case of intravascular lymphoma, which simulates a cerebral vasculitis, is discussed in Chap. 30.
Temporal Arteritis (Giant Cell Arteritis, Cranial Arteritis) (See Also Chap. 9)
In this disease, which is common among older persons, arteries of the external carotid system, particularly the temporal branches, are the sites of a subacute granulomatous inflammatory exudate consisting of lymphocytes and other mononuclear cells, neutrophilic leukocytes, and giant cells. The most severely affected parts of the artery usually become thrombosed. The sedimentation rate is characteristically elevated above 80 mm/h and sometimes exceeds 120 mm/h, but a small number of cases occur with values below 50 mm/h. The disease is included in this chapter because it uncommonly affects the extracranial internal and vertebral arteries and may result in stroke on the basis of ischemic occlusion or secondary embolus. However, significant inflammatory involvement of intracranial arteries from temporal arteritis is uncommon, perhaps because of a relative lack of elastic tissue.
Regional or bilateral headache or head pain is the chief complaint, and there may be severe pain, aching, and stiffness in the proximal muscles of the limbs associated with the markedly elevated sedimentation rate. Thus the clinical picture overlaps that of polymyalgia rheumatica as discussed in Chap. 9. Occlusion of branches of the ophthalmic artery (mainly those to the posterior ciliary artery and the choroidal circulation that supply the anterior optic nerve) results in blindness in one or both eyes, is the most feared complication, often unpredictably. This is one of the main forms of anterior ischemic optic neuropathy discussed in Chap. 12. In a few cases, blindness is preceded by transient visual loss, thereby simulating a TIA (transient monocular blindness). Other symptoms include jaw claudication due to ischemia of the masseter muscles. Occasionally the arteries of the oculomotor nerves are also involved, causing various ophthalmoplegias.