title: Inflammatory myopathy with abundant macrophages (IMAM): a condition sharing similarities with cytophagic histiocytic panniculitis and distinct from macrophagic myofasciitis.
abstract: We describe the unreported pattern of inflammatory myopathy with abundant macrophages (IMAM) as a main differential diagnosis of postimmunization aluminum hydroxide-induced macrophagic myofasciitis (MMF). IMAM was mainly detected among patients with a dermatomyositis (DM)-like disease. Among 113 muscle biopsies from DM patients collected from 1974 to 2000, intensity of macrophage infiltration was highly variable: 41.5% (-/+); 34.5% (+); 17% (++): and 7% (+++). The 27 patients from groups (++) and (+++) had a similar pattern of macrophagic infiltration and were considered to have IMAM. They were compared to 40 MMF patients. In IMAM, macrophage infiltrates were diffuse and correlated positively with both T cell infiltrates and acute muscle fiber damage, and showed pictures of hemophagocytosis (21/27). Connective tissue structures were infiltrated by noncohesive, ribbon-forming collections of large basophilic macrophages containing no crystalline inclusions. In MMF, macrophage infiltrates were focal and formed compact well-delineated aggregates of granular PAS+ cells, loaded with crystalline aluminum hydroxide particles, in the absence of either hemophagocytosis or conspicuous muscle damage. Review of the literature indicates similarities between IMAM and "cytophagic histiocytic panniculitis" (CHP), a condition characterized by T cell-triggered macrophage hyperactivation. Both IMAM and CHP, but not MMF, may be associated with a life-threatening hemophagocytic syndrome.
authors.affiliation: Systeme Neuromusculaire et Inflammation (INSERM, EMI 0011, Université Paris XII-Val de Marne), Département de Pathologie, Hôpital Henri Mondor, Créteil, France.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Bassez
authors.forename: Francois-Jérôme
authors.initials: FJ
authors.lastname: Authier
authors.forename: Emmanuèle
authors.initials: E
authors.lastname: Lechapt-Zalcman
authors.forename: Marie Hélène
authors.initials: MH
authors.lastname: Delfau-Larue
authors.forename: Anne
authors.initials: A
authors.lastname: Plonquet
authors.forename: Michelle
authors.initials: M
authors.lastname: Coquet
authors.forename: Isabel
authors.initials: I
authors.lastname: Illa
authors.forename: Romain K
authors.initials: RK
authors.lastname: Gherardi
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D003937:Diagnosis, Differential; D005208:Fasciitis / Q000473:pathology*; D005260:Female; D005602:France; D006644:Histiocytes; D006801:Humans; D008214:Lymphocytes; D008264:Macrophages; D008297:Male; D008854:Microscopy, Electron; D008875:Middle Aged; D018485:Muscle Fibers, Skeletal / Q000473:pathology; D018482:Muscle, Skeletal / Q000473:pathology*; D009220:Myositis / Q000473:pathology*; D009336:Necrosis; D015434:Panniculitis / Q000473:pathology*