Inflammatory Myopathies: Clinical and Laboratory Features | |||||||||
| DISORDER | SEX | AGE OF ONSET | RASH | PATTERN OF WEAKNESS | LABORATORY FEATURES | MUSCLE BIOPSY | CELLULAR INFILTRATE | RESPONSE TO IS THERAPY | COMMON ASSOCIATED CONDITIONS |
|---|---|---|---|---|---|---|---|---|---|
| DM | F > M | Childhood and adult | Yes | Proximal > distal | Normal or increased CK (up to 50× normal or higher); various MSAs (anti-MDA5, anti-TIF1, anti-Mi-2, anti-NXP2) | Perimysial and perivascular inflammation; IFN-1 regulated proteins (MHC-1, MxA), MAC deposition on capillaries | CD4+ Dendritic cells; B cells; macrophages | Yes | Myocarditis, ILD, malignancy, vasculitis, other CTDs |
| PM | F > M | Adult | No | Proximal > distal | Increased CK (up to 50× normal or higher) | Endomysial and perivascular inflammation; ubiquitous expression of MHC-1 | CD8+ T-cells; macrophages; plasma cells | Yes | Myocarditis, ILD, other CTDs |
| NM | M = F | Children and adults | No | Proximal > distal | Elevated CK (> 10× normal or higher); anti-HMGCR or anti-SRP antibodies | Necrotic muscle fibers; minimal inflammatory infiltrate | Macrophages in necrotic fibers undergoing phagocytosis | Yes | Malignancy, CTD, HMGCR antibody cases can be triggered by statin use |
| ASS | F > M | Children and adults | Sometimes | Proximal > distal | Elevated CK (>10× normal or higher); antisynthetase antibodies | Perimysial and perivascular inflammation; perimysial fragmentation with alkaline phosphatase staining; perimysial muscle damage with necrosis | CD4+ Dendritic cells; B cells; macrophages | Yes | Non-erosive arthritis, ILD, Raynaud phenomenon, mechanic hands, and fever |
| IBM | M > F | Older adults (>50 yrs) | No | Proximal and distal; predilection for: finger/wrist flexors, knee extensors | Normal or mildly increased CK (usually <10× normal); anti-cN-1A antibodies; large granular lymphocytes on flow cytometry and reduced CD4/CD8 ratio with increased CD8 count | Endomysial and perivascular inflammation; ubiquitous expression of MHC-1; rimmed vacuoles; p62, LC3, TDP-43 aggregates; EM: 15-18 nm tubulofilaments; ragged red and COX negative fibers | CD8+ T-cells; macrophages; plasma cells; myeloid dendritic cells; large granular lymphocytes | None or minimal | Granular lymphocytic leukemia/lymphocytosis, sarcoidosis, SICCA or Sjogren's syndrome |
Abbreviations: CK, creatine kinase; cN-1A, cytosolic 5'-nucleotidase 1A; CTDs, connective tissue diseases; COX, cytochrome oxidase; DM, dermatomyositis; F, female; g, immunoglobulin; IBM, inclusion body myositis; IFN-1, type 1 interferon; ILD, interstitial lung disease; IS, immunosuppressive; M, male; MAC, membrane attack complex; MDA5, melanoma differentiation antigen; MHC-1, major histocompatibility antigen 1; NCP2, nuclear matrix protein 2 (NXP2); NM, necrotizing myopathy; PM, polymyositis; TIF1, transcriptional intermediary factor 1.
Source: Adapted with permission from Amato AA, Russell JA (eds): Neuromuscular Disorders, 2nd ed. New York, McGraw-Hill; 2016.