P.19Novel aspects in immune-mediated necrotizing myopathy with pipestem capillaries

Abstract

Immune-mediated necrotizing myopathy with pipestem capillaries are very rare inflammatory myopathies that are characterized by combination of necrotizing myopathy and presence of enlarged capillary walls, strongly staining for complement (C5b-9) and homogeneously thickened basement membranes on electron microscopy. In the past, there have been anecdotal reports on single cases or series of very few patients. Here we report on a series of 15 patients collected during a 10-years period of time. 3/15 of patients suffered from cancer or developed cancer during follow-up. 8/15 of patients had severe systemic inflammatory disease – mostly rheumatologic diseases and 10/15 of them also had nerve involvement including presence of pipestem capillaries and inflammatory changes in sural nerve biopsies. Morphologically, all skeletal muscle biopsies showed sarcolemmal MHC class I stains and many of them showed sarcolemmal MHC class II positivity. Complement (C5b-9) strongly stained capillary walls in 10/15 in the entire biopsy and in 5/15 cases in parts of the biopsy. Strong and complete stain correlated with severe atrophy of the myofibres. We show that atrophic fibers are not regenerating fibers (MHC neo negative) and highlight relevance of molecular markers involved in atrophy. Another interesting feature is presence of numerous cytoplasmic bodies (6/15) and non-rimmed vacuoles (7/15) mostly in severely affected biopsies. This is the largest series of IMNM with pipestem capillaries reported so far. Clinically the association with cancer and with severe inflammatory diseases is of prognostic relevance. Morphologically, we present novel features highlighting atrophy as well as cytoplasmic bodies as relevant features in these biopsies.