Background/Purpose:

Histopathological confirmation is required for the diagnosis of systemic vasculitis. However, patients suspected of vasculitis often only have lesions with a low diagnostic yield for biopsies, such as ENT and lungs. In addition, the biopsy of an involved organ, especially the nerve and kidney, is an invasive procedure carrying the risk of significant complications. In contrast, a muscle biopsy is simple and minimally invasive. However, while the muscle biopsy combined with the nerve biopsy is effective for demonstrating vasculitic neuropathy, the utility of the muscle biopsy alone is uncertain. Herein we assess the accuracy and utility of the muscle biopsy in detecting small-vessel vasculitis (SVV), or medium-vessel vasculitis (MVV) in clinical practice. 

Methods:

Consecutive patients with suspected SVV or MVV seen at our hospital between 2012 and 2014 were prospectively studied. Patients for whom a skin or renal biopsy were indicated were excluded from this study because the skin biopsy is less invasive than the muscle biopsy while the renal biopsy can provide useful information about the severity and prognosis of the disease in addition to its diagnostic value. Muscle biopsies were performed in the bilateral vastus lateralis of the quadriceps femoris because of its hypervascularity unless the patient presented myalgia in the other muscles. Imaging studies of muscles were not routinely performed. The definition of a positive muscle biopsy was the presence of inflammatory infiltrates with fibrinoid necrosis in the vessels. 

Results:

Forty-seven patients underwent muscle biopsies. Diagnosis of SVV or MVV was made in 34 patients in the follow-up period lasting more than six months. An unrelated condition was diagnosed in ten patients while nothing could be diagnosed in three patients. Of the 34 patients in whom SVV or MVV was diagnosed, a positive muscle biopsy was obtained in 20 patients (15 with MPA, 3 with PN, and 2 with EGPA) while other findings led to the same diagnosis in 14 (7 with MPA, 3 with GPA, 3 with PN, 1 with rheumatoid vasculitis). The sensitivity of the muscle biopsy was 59%.  Of the 12 patients presenting vasculitic neuropathy, muscle biopsies demonstrated vasculitis in nine patients, with 75% sensitivity. Myalgia was seen in ten (50%) vasculitis patients with positive biopsies and in two (14.3%) patients with negative biopsies (p = 0.031). There were no complications in the procedure except for delayed wound healing in one patient.

Conclusion:

The muscle biopsy is a safe method which offers a high diagnostic yield in diagnosing SVV or MVV in the absence of indications for a skin or renal biopsy. Further, the muscle biopsy can be used in place of the nerve biopsy for diagnosing vasculitis in patients with vasculitic neuropathy.

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« Back to 2014 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-muscle-biopsy-is-a-useful-and-noninvasive-procedure-in-diagnosing-systemic-vasculitis-affecting-small-to-medium-sized-vessels-a-prospective-evaluation/