Abstract Details

Title Pathological Changes of Necrotizing Autoimmune Myopathy Associated with Anti-Signal Recognition Particle Antibody

Topic Muscle Disease/Neuromuscular Junction

Presentation(s) P07 - (-)

Poster/Presentation
Number 044

Objective

Background BACKGROUND: Necrotizing autoimmune myopathy (NAM) is an entity of idiopathic inflammatory myopathies. The cause of NAM is multifactorial, and it has been known that some of the patients with NAM associate with anti-signal recognition particle antibody. Although it has been suggested that SRP-NAM is caused by vasculopathy mediated by complement deposition on endomysial vessels, the details of its pathogenesis have not been clarified yet.

Design/Methods DESIGN/METHODS: Twenty-four patients with SRP-NAM (M10, F14) screened from 504 consecutive myositis patients were analyzed. All showed weakness in the limbs and elevated serum CK levels (2661-13804 IU/L; average,6987 IU/L). Muscle biopsy samples before treatment were obtained for routine, immunohistochemical analysis and electron microscopy observation and pathological findings were semi quantitatively analyzed.

Results RESULTS: The extents of (necrotic fiber/lymphocytic infiltration) were severe (15/2), moderate (7/2), mild to none (2/20). The increased expression of (MHC-classI/II) antigens on the sarcolemma of non-necrotic fibers increased in (3/0). In the immunohistochemical analysis of complement C5b9, five patients showed granular staining of vessels in the endomysium. Electron microscopy observation of the vessels in the endomysium in 16 patients (30-126 vessels were observed/patient) showed tubule reticular particles in endothelial cells of the vessels in six patients and destroyed endomysial vessels in five patients (average 3% of the observed vessels).

Conclusions CONCLUSIONS: In this study, the number of the patients with complement C5b9 deposition on endomysial vessels and the number of the patients with destroyed endomysial vessels were small. Thus, our data did not indicate that vascuopathy is the main pathomechanism of SRP-NAM. Further studies are necessary to clarify the cause of muscle fiber damage in SRP-NAM.

Authors/Disclosures
Jun Shimizu, MD, PhD (Tokyo University of Technology) PRESENTER	No disclosure on file
Meiko Maeda, MD, PhD (Tokyo university)	No disclosure on file
	No disclosure on file
Shoji Tsuji, MD, PhD (University of Tokyo)	The institution of Dr. Tsuji has received research support from Novelpharma Co. Ltd..
Saroja A.O.	Saroja A.O. has nothing to disclose.

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