title: Signal recognition particle immunoglobulin g detected incidentally associates with autoimmune myopathy.
abstract: 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.
  
  
  
  Distinctive cytoplasm-binding IgG (mouse tissue substrate) prompted western blot, enzyme-linked immunoassay, and immunoprecipitation analyses. Available histories were reviewed.
  
  
  
  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.
  
  
  
  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.
authors.affiliation: Department of Laboratory Medicine and Pathology, Mayo Clinic, 200 First Street SW, Rochester, Minnesota, 55905, USA.
authors.forename: Metha
authors.initials: M
authors.lastname: Apiwattanakul
authors.affiliation: Department of Neurology, Mayo Clinic, Rochester, Minnesota, USA.
authors.forename: Margherita
authors.initials: M
authors.lastname: Milone
authors.affiliation: Department of Laboratory Medicine and Pathology, Mayo Clinic, 200 First Street SW, Rochester, Minnesota, 55905, USA.|Department of Neurology, Mayo Clinic, Rochester, Minnesota, USA.
authors.forename: Sean J
authors.initials: SJ
authors.lastname: Pittock
authors.affiliation: Department of Laboratory Medicine and Pathology, Mayo Clinic, 200 First Street SW, Rochester, Minnesota, 55905, USA.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Kryzer
authors.affiliation: Department of Laboratory Medicine and Pathology, Mayo Clinic, 200 First Street SW, Rochester, Minnesota, 55905, USA.
authors.forename: James P
authors.initials: JP
authors.lastname: Fryer
authors.affiliation: Department of Neurology, Mayo Clinic, Rochester, Minnesota, USA.
authors.forename: Orna
authors.initials: O
authors.lastname: O'toole
authors.affiliation: Department of Laboratory Medicine and Pathology, Mayo Clinic, 200 First Street SW, Rochester, Minnesota, 55905, USA.|Department of Neurology, Mayo Clinic, Rochester, Minnesota, USA.
authors.forename: Andrew
authors.initials: A
authors.lastname: Mckeon
authors.affiliation: Department of Laboratory Medicine and Pathology, Mayo Clinic, 200 First Street SW, Rochester, Minnesota, 55905, USA.|Department of Neurology, Mayo Clinic, Rochester, Minnesota, USA.|Department of Immunology, Mayo Clinic, Rochester, Minnesota, USA.
authors.forename: Vanda A
authors.initials: VA
authors.lastname: Lennon
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000951:Antigens, Neoplasm / Q000276:immunology; D001327:Autoimmune Diseases / Q000097:blood / Q000150:complications / Q000276:immunology; D001921:Brain / Q000378:metabolism / Q000473:pathology; D004576:Electromyography; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D005968:Glutamate Decarboxylase; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood* / Q000378:metabolism; D047468:Immunoprecipitation; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000378:metabolism / Q000473:pathology; D009135:Muscular Diseases / Q000097:blood / Q000150:complications / Q000276:immunology; D009474:Neurons / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D018271:Signal Recognition Particle / Q000145:classification / Q000235:genetics / Q000276:immunology*; D055815:Young Adult
chemical_list: D000951:Antigens, Neoplasm; D007074:Immunoglobulin G; C505096:PCA-1 antigen, human; D012333:RNA, Messenger; D018271:Signal Recognition Particle; D005968:Glutamate Decarboxylase; C401141:glutamate decarboxylase 2
keywords: autoantibody; necrotizing myopathy; paraneoplastic; serological marker