Inflammatory myopathy with abundant macrophages (IMAM): a condition sharing similarities with cytophagic histiocytic panniculitis and distinct from macrophagic myofasciitis

J Neuropathol Exp Neurol. 2003 May;62(5):464-74. doi: 10.1093/jnen/62.5.464.


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.

Publication types

  • Case Reports
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • Child
  • Child, Preschool
  • Diagnosis, Differential
  • Fasciitis / pathology*
  • Female
  • France
  • Histiocytes*
  • Humans
  • Lymphocytes
  • Macrophages*
  • Male
  • Microscopy, Electron
  • Middle Aged
  • Muscle Fibers, Skeletal / pathology
  • Muscle, Skeletal / pathology*
  • Myositis / pathology*
  • Necrosis
  • Panniculitis / pathology*