[Vasculitic involvement of the skeletal muscle and the peripheral nervous system: clinical and neuropathologic...

The peripheral nervous system is a classic target organ in systemic vasculitis. In addition, the skeletal muscle can also be affected. Myalgia, muscle weakness and sensory deficits are typical signs, which can lead to severe functional limitations and impaired of quality of life. Vasculitic involvement of the skeletal muscle (vasculitic myopathy [VM]) and peripheral nerves (vasculitic neuropathy [VN]) occurs predominantly in polyarteritis nodosa and small-vessel vasculitis. VM presents with elevated markers of inflammation and is typically characterized by immobilizing myalgia with normal creatine kinase activity and diffuse or patchy areas of hyperintensity on T2-weighted MRI ("MRI myositis without myositis"). In VN, sensor motor deficits predominantly affect the lower extremity in the area supplied by several peripheral nerves (e.g., mononeuritis multiplex) with acute to subacute history. The histopathological examination of nerve and muscle biopsies is the gold standard for the diagnosis of vasculitic manifestations and has a significant impact on the therapeutic approach.