Statin-associated autoimmune myopathy: A distinct new IFL pattern can increase the rate of HMGCR antibody detection by clinical laboratories

Abstract

Background and objective: Statin-associated autoimmune myopathy (SAAM) with anti-HMGCR antibodies has recently been described. Several specific immunoassays are in use to detect HMGCR antibodies. In the course of systematic autoantibody screening we recognized a new distinct IFL staining pattern on rat liver sections that regularly coincided with anti-HMGCR antibodies. In this study we investigated whether this new IFL pattern is specifically associated to statin-associated autoimmune myopathy and corresponds to anti-HMGCR antibodies.

Patients and methods: Twenty-three patients positive for anti-HMGCR antibodies (14 diagnosed with SAAM) were investigated for anti-HMGCR antibodies by two ELISA assays and confirmed by immmunoblot. HMGCR associated liver IFL pattern (HALIP) was detected by indirect IFL and the reactivity against HMGCR was confirmed by immunoabsorption using purified human HMGCR antigen. 90 patients with other autoimmune diseases and 45 non-autoimmune statin treated patients were studied as controls.

Results: 21 out of 23 (91%) anti-HMGCR positive patients were HALIP positive. The staining was completely and specifically removed by immunoabsorption with human purified HMGCR. None of the control sera from autoimmune patients or non-autoimmune statin treated subjects was positive for HALIP. Statistical concordance between HALIP and anti-HMGCR antibody specific tests was 98.7%, kappa 0.95.

Conclusions: A new and distinct IFL staining pattern (HALIP) is associated to HMGCR associated myopathy. Absorption and concordance studies indicate that the antigen recognized in the liver by HALIP is HMGCR or a closely related protein. Awareness of this new pattern can help to detect HMGCR autoantibodies in statin treated patients tested for autoimmune serology.

Keywords: Anti-HMGCR; Blot; ELISA; HALIP pattern; Immunofluorescence pattern; Myositis; Statin-associated autoimmune myopathy.

Fig. 1.

Patient flow chart. SAAM: statin-associated autoimmune myopathy; DM: dermatomyositis; PM: polymyositis; SLE: systemic lupus erithematosus; SSc: systemic sclerosis; SS: Sjögren syndrome: RA: rheumatoid arthritis

Fig. 2.

The HALIP staining. Indirect immunofluorescence on rat liver cryostat section. Patient serum was followed by FITC anti-IgG antisera (for detail see methods). The image was obtained with a spectral confocal microscope FV1000 (Olympus). Notice the clear cytoplasmic staining in distinct scattered hepatocytes, with a granular texture in the inset (original magnification ×200 in the main picture and ×1000 in the inset).

Fig. 3.

Anti-HMGCR IFL pattern produced in rat liver by an anti-HMGCR positive serum, using substrate slides from different commercial suppliers. a) Inova Slides. b) Euroimmune. c) BioSystems. d) Aeskulides Diagnostics.

Fig. 4.

Immunoabsorption experiment: a) IIF given by an anti-HMGCR negative control sera. b) IIF pattern produced by anti-HMGCR positive serum from patient A. C. sera from patient A after immunoabsorption with human antigen HMGCR at concentration of 1.68 μg/m. d) Sera from patient A after immunoabsorption with human antigen HMGCR at concentration of 6.74 μg/ml. (INOVA Diagnostics, Inc., San Diego Lite @ rat kidney/stomach/liver slides).