**5. Diagnosis and clinical results of peripheral neuropathy in ANCA-associated vasculitis**

The diagnosis of vasculitis neuropathy in AAV is usually easier in patients already presenting with multiorgan involvement and mononeuropathy multiplex. However, the diagnosis may be more cumbersome in less typical presentations of AAV or when peripheral neuropathy is the unique manifestation of the disease.

## *Peripheral Neuropathy in ANCA Vasculitis DOI: http://dx.doi.org/10.5772/intechopen.101241*

In these situations, the diagnosis is helped by focusing on the medical history, physical examination, electrodiagnostic study and nerve biopsy. Electrodiagnostic testing reveal an axonal neuropathy with reduced sensory and motor nerve action potential amplitudes [25–28] with better preservation of the nerve conduction velocities and distal latencies. These findings are more often in the lower limbs [28]. The nerve biopsy should be guided by the nerve conduction studies and include the nerve and neighboring muscle, such as sural nerve and neighboring gastrocnemius or superficial peroneal nerve biopsy and peroneus brevis muscles [17, 22, 29–31]. Muscle biopsy may increase the diagnostic sensitivity when concomitantly performed with the nerve biopsy [32]. Nerve biopsy results supportive of vasculitic neuropathy include the presence of vessel wall inflammation with vascular damage; vascular deposits of immunoglobulin M, C3, or fibrinogen, hemosiderin deposits on direct immunofluorescence, asymmetric nerve fiber loss, prominent active axonal degeneration, and myofiber necrosis, regeneration, or infarcts in the peroneus brevis muscle biopsy [23, 32].
