Signal recognition particle immunoglobulin g detected incidentally associates with autoimmune myopathy.

Abstract

INTRODUCTION:

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.

• Authors: Metha Apiwattanakul, Margherita Milone, Sean J Pittock, Thomas J Kryzer, James P Fryer, Orna O'toole, Andrew Mckeon, Vanda A Lennon
• Journal: Muscle & nerve (Muscle Nerve) Vol. 53 Issue 6 Pg. 925-32 (06 2016) ISSN: 1097-4598 [Electronic] United States
• PMID: 26561982 (Publication Type: Journal Article)
• Copyright: © 2015 The Authors. Muscle & Nerve Published by Wiley Periodicals, Inc.

Chemical References

• Antigens, Neoplasm
• Immunoglobulin G
• PCA-1 antigen, human
• RNA, Messenger
• Signal Recognition Particle
• Glutamate Decarboxylase
• glutamate decarboxylase 2

Topics

• Adolescent
• Adult
• Aged
• Aged, 80 and over
• Antigens, Neoplasm (immunology)
• Autoimmune Diseases (blood, complications, immunology)
• Brain (metabolism, pathology)
• Electromyography
• Enzyme-Linked Immunosorbent Assay
• Female
• Glutamate Decarboxylase
• Humans
• Immunoglobulin G (blood, metabolism)
• Immunoprecipitation
• Male
• Middle Aged
• Muscle, Skeletal (metabolism, pathology)
• Muscular Diseases (blood, complications, immunology)
• Neurons (metabolism)
• RNA, Messenger (metabolism)
• Signal Recognition Particle (classification, genetics, immunology)
• Young Adult