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Signal recognition particle immunoglobulin g detected incidentally associates with autoimmune myopathy
Author(s) -
Apiwattanakul Metha,
Milone Margherita,
Pittock Sean J.,
Kryzer Thomas J.,
Fryer James P.,
O'toole Orna,
Mckeon Andrew,
Len Vanda A.
Publication year - 2016
Publication title -
muscle and nerve
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.025
H-Index - 145
eISSN - 1097-4598
pISSN - 0148-639X
DOI - 10.1002/mus.24970
Subject(s) - autoantibody , myopathy , medicine , pathology , antibody , immunology
: Paraneoplastic autoantibody screening of 150,000 patient sera by tissue‐based immunofluorescence incidentally revealed 170 with unsuspected signal recognition particle (SRP) immunoglobulin G (IgG), which is a recognized biomarker of autoimmune myopathy. Of the 77 patients with available information, 54 had myopathy. We describe the clinical/laboratory associations. Methods : Distinctive cytoplasm‐binding IgG (mouse tissue substrate) prompted western blot, enzyme‐linked immunoassay, and immunoprecipitation analyses. Available histories were reviewed. Results : The immunostaining pattern resembled rough endoplasmic reticulum, and mimicked Purkinje‐cell cytoplasmic antibody type 1 IgG/anti‐Yo. Immunoblotting revealed ribonucleoprotein reactivity. Recombinant antigens confirmed the following: SRP54 IgG specificity alone (17); SRP72 IgG specificity alone (3); both (32); or neither (2). Coexisting neural autoantibodies were identified in 28% (low titer). Electromyography revealed myopathy with fibrillation potentials; 78% of biopsies had active necrotizing myopathy with minimal inflammation, and 17% had inflammatory myopathy. Immunotherapy responsiveness was typically slow and incomplete, and relapses were frequent on withdrawal. Histologically confirmed cancers (17%) were primarily breast and hematologic, with some others. Conclusions : Autoimmune necrotizing SRP myopathy, both idiopathic and paraneoplastic, is underdiagnosed in neurological practice. Serological screening aids early diagnosis. Cancer surveillance and appropriate immunosuppressant therapy may improve outcome. Muscle Nerve 53 : 925–932, 2016