Vasculitic neuropathy can be a part of systemic vasculitis. It also can present as a nonsystemic vasculitic neuropathy, without any constitutional symptoms or serologic abnormalities. The clinical and pathologic features are those of an ischemic neuropathy caused by a necrotizing vasculitis of small arterioles.
Patients with vasculitic neuropathy may present with either mononeuritis multiplex or asymmetric sensorimotor neuropathy. Symmetric neuropathy is rare. It can present as acute/subacute relapsing, progressive, or relapsing progressive neuropathy.
Asymmetric or multifocal painful sensorimotor neuropathy is the most common presentation.
Asymmetry and length-independent involvement are the hallmarks of mononeuritis multiplex, which is the most common presenting feature of vasculitic neuropathy.
Less than 3% of the world's population is affected but is found that over half of the people suffering from diabetics will develop some degree of nerve damage. The symptoms of neuropathy are usually the only method of diagnosis. Symptoms may involve tingling sensations similar to decreased circulation in the extremities such as numbness or even and pins and needles. A person's limbs may feel alternately burning hot and icy cold, accompanied by sharp or dull pain and muscle fatigue. These feelings are associated with reduced fine motor coordination, possibly leading to paralysis in extreme cases.
It is easy to diagnose neuropathy based on the pain suffered by a patient but it is difficult to treat because neuropathy is so commonly idiopathic, which means the doctor doesn't know why the patient has developed peripheral nerve damage. However, some of the causes identified include malnutrition, repetitive motion resulting in carpal tunnel syndrome, herpes virus, HIV/AIDS, exposure to toxins such as alcohol and inherited genetic disorders. When a doctor can identify one of these causes, they can treat the pain at the source by correcting malnutrition or treating diabetes for example. Unfortunately, if the neuropathy is idiopathic, the only available treatment is ongoing, temporary pain management usually with pharmaceutical products. Researchers are still pursuing many paths of study to better understand the process that leads to such widespread neuropathy.
Wallerian degeneration of nerves results from ischemic infarction caused by inflammatory occlusion of the blood vessels. Segmental fibrinoid necrosis of a vessel wall and transmural inflammatory cell infiltration are the main pathologic features of vasculitis. Leukocytoclastic reaction traditionally has been considered the primary mechanism of vessel injury in these diseases, although more recent evidence suggests that cellular-mediated mechanisms may be more important in the peripheral nerve.
Immune complexes are formed as a result of antibodies reacting with antigen found within the blood vessel walls. These immune complexes within the circulation activate the complement cascade, generating chemotactic factors responsible for recruitment of polymorphonuclear leukocytes at the local site of deposition of the complex. Degranulation of the polymorphonuclear leukocytes releases proteolytic enzymes, which, along with free radicals, disrupt cell membranes and damage blood vessels. T cell–mediated processes against epineurial and endoneurial vessels likely are also important in the pathogenesis of vasculitic neuropathies.
Necrotizing vasculitis causes neuropathy through ischemic injury to the vessels supplying the nerve. Poor collateral circulation in the nerves makes them susceptible to ischemic injuries. Commonly involved nerves with these features tend to be in the mid upper arm and mid thigh in the "watershed zone."
Vasculitic neuropathy most often presents as mononeuropathy multiplex (ie, in more than 60% of patients), with the peroneal nerve most commonly affected (89% of patients), followed by the sural nerve (84%), tibial nerve (68%), ulnar nerve (42%), and median nerve (26%).
Distal symmetric polyneuropathy is the second most common presentation, seen in less than one third of patients. The nerves most often affected clinically are a diffuse mix of distal more than proximal lower limb nerves, arising either from the lumbosacral plexus or from widespread multifocal nerve involvement (ie, summation of existing patchy lesions).
Cranial nerve involvement also has been reported in systemic vasculitis. Facial nerve neuropathy is observed most commonly, occasionally accompanied by abnormalities in cranial nerve III, VI, or X.