Early skeletal muscle manifestations in polyarteritis nodosa and ANCA-associated vasculitis

Skeletal muscle involvement is common in patients with small- and medium-sized vasculitis, particularly polyarteritis nodosa (PAN) and antineutrophil cytoplasmic antibody-associated vasculitis (AAV). Despite being not included in the standard classification criteria for PAN and AAV, skeletal muscle involvement is an important clinical indicator, particularly when vasculitic myopathy is the only pathological evidence in the absence of other organ involvement. Herein, we comprehensively reviewed and compared the clinical features of 71 and 135 patients with PAN and AAV, respectively, with skeletal muscle involvement at the time of disease onset. Most patients with PAN and AAV exhibited skeletal muscle involvement, often characterized by myalgia and occasional muscular weakness, predominantly in the lower extremities. Myalgia and weakness were observed more frequently in the distal lower extremities in patients with PAN than in those with AAV. In contrast, skeletal muscle involvement tended to exhibit a more dispersed distribution across all four extremities in those with AAV. Muscle magnetic resonance imaging T2-weighted and short-tau inversion recovery sequences can effectively identify hyperintense areas attributed to hypervascularity of affected muscle tissues and serve as a sensitive and useful modality for visually determining the suitable biopsy site. >90% of patients with PAN and AAV demonstrated perivascular inflammation in their affected muscle tissues, whereas fibrinoid necrosis of the vessel walls was reported in two-thirds of patients. Serum creatine kinase (CK) levels were within the normal range in approximately 80% of patients presenting with skeletal muscle involvement in PAN and AAV. Furthermore, muscle fiber damage was milder in patients with skeletal muscle involvement in PAN and AAV than those with idiopathic inflammatory myositis. Meanwhile, serum CK levels were elevated in 65-85% of patients with PAN and AAV who had myofiber necrosis and degeneration in the affected muscles. Most patients with PAN and AAV showed improvement in skeletal muscle involvement following glucocorticoids (GCs) administration; however, relapse was observed in some patients during the tapering of GCs. In summary, skeletal muscle involvement is a potential indicator for establishing PAN and AAV diagnoses during the early phases of the disease.

Inflammatory muscle involvement in systemic vasculitis: A systematic review

Vasculitis are severe systemic autoimmune diseases which may involve different organs and systems. Conversely, muscles do not represent an organ commonly involved by systemic vasculitis and myositis is not include among any classification or diagnostic criterion of vasculitis. In this regard, we aimed to review the literature in order to report all the available evidence concerning the inflammatory involvement of muscle in patients affected by systemic vasculitis. We collected a total of 108 papers, for a sum of 395 patients affected by muscle vasculitis. Most of them suffered from medium and small vessels vasculitis (mainly polyarteritis nodosa and ANCA-associated vasculitis) or from vasculitis secondary to rheumatoid arthritis. Conversely, muscle involvement in case of large vessel vasculitis occurred seldom, while only few papers reported such occurrence in Kawasaki or Behçet's disease. Histological findings may differ, but the most common ones displayed a necrotizing vasculitis of perimysium vessels, while granulomatous vasculitis was assessed only in case of ANCA-associated vasculitis patients. Creatine kinase were usually within normal range, seldom elevated, while imaging findings were generally undistinguishable from the ones found in idiopathic inflammatory myopathies: magnetic resonance imaging displays signal hyperintensity in T2 and STIR scans, while few data exist for positron emission tomography. The presentation of the disease may be fearsome and severe, sometimes life-threatening, but an overall good response to conventional immunosuppressants and/or glucocorticoids has been reported.

Polyarteritis nodosa isolated to muscles-A case series with a review of the literature

Muscular polyarteritis nodosa where disease is isolated to skeletal muscle is a rare and often poorly recognised clinical entity. Patients typically present with fever and severe muscle pain limiting ability to ambulate without rise in creatine kinase. Often there is a significant delay between presentation and diagnosis, which requires histological confirmation. Musculoskeletal MRI is a sensitive investigation that can lead to timely biopsy and improve diagnostic yield. Early diagnosis of this condition is essential as patients typically respond favourably to corticosteroid treatment. Here we report 4 cases of muscular polyarteritis nodosa and review the reported literature.

Muscular vasculitis confined to lower limbs: description of two case reports and a review of the literature

Muscular involvement is common during systemic vasculitides, such as polyarteritis nodosa. However, in rare cases, muscular involvement can be the only clinically evident feature of the disease. The clinical pattern of isolated muscular vasculitis may mimic several other inflammatory muscle disorders, such as idiopathic inflammatory myositis, and may represent a challenge in differential diagnosis. Herewith, we present two clinical cases as examples of peculiar clinical and histopathological characteristics of isolated muscular vasculitis. Our patients were successfully treated with steroids and immunosuppressive agents. Moreover, we provide a review of the recent existing medical literature. Our cases suggest the importance of performing muscle biopsy in patients with muscular symptoms to guide the diagnosis and the treatment.