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

Effects of HMGCR deficiency on skeletal muscle development

Pathogenic variants in HMGCR were recently linked to a limb-girdle muscular dystrophy (LGMD) phenotype. The protein product HMG CoA reductase (HMGCR) catalyzes a key component of the cholesterol synthesis pathway. The two other muscle diseases associated with HMGCR, statin-associated myopathy (SAM) and autoimmune anti-HMGCR myopathy, are not inherited in a Mendelian pattern. The mechanism linking pathogenic variants in HMGCR with skeletal muscle dysfunction is unclear. We knocked down Hmgcr in mouse skeletal myoblasts, knocked down hmgcr in Drosophila, and expressed three pathogenic HMGCR variants (c.1327C>T, p.Arg443Trp; c.1522_1524delTCT, p.Ser508del; and c.1621G>A, p.Ala541Thr) in Hmgcr knockdown mouse myoblasts. Hmgcr deficiency was associated with decreased proliferation, increased apoptosis, and impaired myotube fusion. Transcriptome sequencing of Hmgcr knockdown versus control myoblasts revealed differential expression involving mitochondrial function, with corresponding differences in cellular oxygen consumption rates. Both ubiquitous and muscle-specific knockdown of hmgcr in Drosophila led to lethality. Overexpression of reference HMGCR cDNA rescued myotube fusion in knockdown cells, whereas overexpression of the pathogenic variants of HMGCR cDNA did not. These results suggest that the three HMGCR-related muscle diseases share disease mechanisms related to skeletal muscle development.

Anti-HMGCR immune-mediated necrotising myopathy: Addressing the remaining issues

The discovery of autoantibodies directed against the 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) enzyme has defined a sub-set of immune-mediated necrotising myopathy (IMNM) which is strongly associated with exposure to statin medications. Although understanding of anti-HMGCR IMNM has grown considerably with the reporting of multiple cohorts in North America, Europe, Asia and Oceania, there remain many unanswered questions. The true incidence of anti-HMGCR IMNM is not known and heterogeneity of phenotype and treatment response within this autoantibody sub-group is being increasingly recognised. Statin-naïve adults and juvenile patients with anti-HMGCR potentially share characteristics distinct from statin-exposed patients, alluding to unique pathogenesis. Conflicting data exists on whether malignancies are associated with anti-HMGCR and further clarification is required to determine the degree of cancer screening required. Treatment approaches to anti-HMGCR IMNM are heterogeneous but generally highlight the efficacy of intravenous immunoglobulin. Even with multimodal immunosuppression, patients with anti-HMGCR remain prone to relapse, with younger patients generally manifesting more refractory disease. In this Review, we aim to summarise the current literature on anti-HMGCR and discuss the remaining issues.

Epidemiological and genetic features of anti-3‑hydroxy-3-methylglutaryl-CoA reductase necrotizing myopathy: Single-center experience and literature review

OBJECTIVE

To characterize the demographic, genetic, clinical, and serological features of patients with anti-3‑hydroxy-3-methylglutaryl-CoA reductase (HMGCR) immune-mediated necrotizing myopathy (IMNM) in a region of northern Spain.

METHODS

Study of all patients diagnosed with anti-HMGCR IMNM during a 5-year period at a reference hospital in northern Spain. Besides clinical and laboratory data, we analyzed the genetic influence of HLA genes and the rs4149056 (c.521T>C) single nucleotide polymorphism (SNP) in the SLCO1B1 gene.

RESULTS

8 patients (5 women, 3 men) with a mean ± SD age of 64.9 ± 7.3 years, fulfilled the criteria for anti-HMGCR IMNM. The incidence rate was 0.6 per 100.000 person-years and the prevalence 3 per 100.000 population. All patients had been exposed to statins. All of them had predominant lower limb proximal and symmetric muscle weakness that was severe in 2 and had elevated serum CK levels with a median [IQR] of 4488 [2538-9194] IU/L. Serum 25‑hydroxy vitamin D levels were decreased in all patients in whom it was determined. The 3 patients with a previous diagnosis of hypothyroidism had abnormal levels of TSH at the time of diagnosis. All patients experienced improvement with different schemes of immunosuppressive therapy. Noteworthy, 7 of 8 patients carried the HLA-DRB1*11 allele. The frequency of the rs4149056 C allele in the SLCO1B1 gene (12.5%) was similar to that of the general population.

CONCLUSION

In northern Spain, anti-HMGCR IMNM preferentially affects people over 50 years of age who are carriers of the HLA-DRB1*11 allele and take statins. Both low vitamin D levels and hypothyroidism may play a potential predisposing role in the development of this disease.

Anti-HMGCR myopathy overlaps with dermatomyositis-like rash: a distinct subtype of idiopathic inflammatory myopathy

OBJECTIVE

To characterize the clinical and pathological features of anti-HMGCR myopathy.

METHODS

The presence of anti-HMGCR antibody in the serum of 227 patients with idiopathic inflammatory myopathy (IIM) and 100 healthy control individuals was assessed by ELISA. All ELISA positive samples were retested by indirect immunofluorescence assay (IIFA) on HEK293 cells. The clinical findings, muscle pathological features, and treatment outcomes of patients with anti-HMGCR myopathy, along with comparisons between anti-HMGCR myopathy with and without dermatomyositis (DM)-like skin rashes, and among MSA-based subgroups were analyzed.

RESULTS

We established an optimized ELISA cutoff for anti-HMGCR antibody positivity as ≥ 5.28 U. The overall concordance between ELISA and IIFA was 96.83%. Twenty-one out of 227 IIM patients were anti-HMGCR-positive by both assays. Of these 21 patients, 9 had DM-like skin rashes, and 16 showed remarkable muscle inflammation; 5 patients were juvenile-onset, and 2 received statin treatment. The muscle biopsies from these patients demonstrated variable muscle necrosis and T cell infiltration. Most anti-HMGCR-positive patients achieved favorable outcomes following prednisone and additional immunotherapies. The anti-HMGCR myopathy patients with DM-like rashes, compared to those without DM-like rashes, were younger and had a shorter disease duration.

CONCLUSIONS

Optimization of cutoff of anti-HMGCR antibody assays with confirmation by alternative assays can result in higher sensitivity and specificity. DM-like skin rashes and lymphocytic infiltrates were not rare in patients with anti-HMGCR myopathy. These findings suggest that while anti-HMGCR myopathy may overlap with DM-like rash, it is pathologically different from classic DM, and should be considered a distinct subgroup of IIM.

Cancer screening in idiopathic inflammatory myopathies: Ten years experience from a single center

OBJECTIVE

There is a well-recognized association between cancer and myositis, so cancer screening at diagnosis is recommended. We aim to report the results of our cancer screening strategy and to ascertain the reliability of using PET/CT to identify cancer-associated myositis (CAM) in a large cohort of patients with myositis from a single center over 10 years.

METHODS

This retrospective observational study included all patients diagnosed with any type of myositis except for inclusion body myositis. Cancer screening strategy was individualized according to clinical and serological data, including PET/CT as the main test to detect occult cancer (OC). Procedures derived from a positive PET/CT were registered. Qualitative data expressed as percentages, and quantitative data as the median with the interquartile range were analyzed. A ROC curve was used to estimate the reliability of PET/CT for CAM diagnosis.

RESULTS

Seventy-seven out of 131 patients underwent a PET/CT for OC screening. The performance of the PET/CT in patients with myositis at disease onset yielded an area under the curve ROC of 0.87 (0.73-0.97) for CAM diagnosis. Invasive procedures in 7 (9%) patients without a final diagnosis of cancer did not cause derived complications. Patients not evaluated for OC did not develop cancer after a median follow-up of 3.3 years (1.7-6.7).

CONCLUSION

Cancer screening strategy should be individualized. PET/CT at myositis onset seems to be an efficient approach to rule out CAM. This practice does not seem to significantly increase harm to patients related to the additional tests needed to clarify inconclusive results.

Atorvastatin-Induced Necrotizing Myopathy and its Response to Combination Therapy

Atorvastatin is the most commonly used statin medication to decrease cholesterol levels and prevent atherosclerosis. Myopathy is a reported side effect of atorvastatin which can happen even after more than six months after starting the medication. The side effect on the muscle tissue can range from simple reversible myalgia to respiratory muscle compromise. Here we present a 46-year-old male who presented with myopathy after taking atorvastatin for two years. Biopsy proved immune-mediated necrotizing myopathy which responded to a combination of Rituximab and intravenous immunoglobulin therapy.

Anti-HMGCR Specificity of HALIP: A Confirmatory Study

A distinctive new indirect immunofluorescence pattern in liver tissue has been associated with anti-HMGCR autoantibodies. It is known as HALIP (HMGCR Associated Liver Immunofluorescence Pattern). In this study, we furthered the original studies to demonstrate the association of anti-HMGCR antibodies with the HALIP. Human anti-HMGCR antibodies from patients’ sera were purified and incubated with rat triple tissue (kidney/stomach/liver). A characteristic HALIP was observed. Additionally, a colocalization assay of human anti-HMGCR antibodies with rabbit polyclonal anti-HMGCR antibodies showed colocalization of both immunofluorescence patterns. This study confirms that the HALIP is due to human anti-HMGCR antibodies.

Statin-Associated Autoimmune Myopathy: Current Perspectives

Although generally well tolerated, statin users frequently report muscle-related side effects, ranging from self-limiting myalgias to rhabdomyolysis or the rare clinical entity of statin-associated immune-mediated necrotizing myopathy (IMNM). Statin-associated IMNM is based on the development of autoantibodies against 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR), the rate-limiting enzyme in cholesterol synthesis and the pharmacologic target of statins, and leads to a necrotizing myopathy requiring immunosuppressive therapy. This review attempts to recapitulate the diverse aspects of anti-HMGCR IMNM, including clinical presentation, diagnostic modalities, genetic risk associations, therapeutic options and potential pathogenetic pathways.

Disease Specific Autoantibodies in Idiopathic Inflammatory Myopathies

Idiopathic inflammatory myopathies represent still a diagnostic and therapeutic challenge in different disciplines including neurology, rheumatology, and dermatology. In recent years, the spectrum of idiopathic inflammatory myopathies has been significantly extended and the different manifestations were described in more detail leading to new classification criteria. A major breakthrough has also occurred with respect to new biomarkers especially with the characterization of new autoantibody-antigen systems, which can be separated in myositis specific antibodies and myositis associated antibodies. These markers are detectable in approximately 80% of patients and facilitate not only the diagnostic procedures, but provide also important information on stratification of patients with respect to organ involvement, risk of cancer and overall prognosis of disease. Therefore, it is not only of importance to know the significance of these markers and to be familiar with the optimal diagnostic tests, but also with potential limitations in detection. This article focuses mainly on antibodies which are specific for myositis providing an overview on the targeted antigens, the available detection procedures and clinical association. As major tasks for the near future, the need of an international standardization is discussed for detection methods of autoantibodies in idiopathic inflammatory myopathies. Furthermore, additional investigations are required to improve stratification of patients with idiopathic inflammatory myopathies according to their antibody profile with respect to response to different treatment options.

Myositis-specific autoantibodies, a cornerstone in immune-mediated necrotizing myopathy

Over the past few years, myositis-specific autoantibodies played an increasing role in the inflammatory idiopathic myositis definition. They became the critical immunological marker for immune-mediated necrotizing myopathy diagnosis (IMNM) since the paradigm switch from histological to serological criteria. This review is focused on the key role of the anti-signal recognition particle (anti-SRP) and the anti-3-Hydroxy-3-MethylGlutaryl-Coenzyme A Reductase (anti-HMGCR) antibodies in immune-mediated necrotizing myopathy. Anti-SRP and anti-HMGCR antibodies are robust diagnostic tools in case of both the classical subacute form and the slowly progressive form of IMNM that may mimic muscular dystrophy. Anti-SRP and anti-HMGCR patients share clinical, biological and histological features with some antibody-associated specificity. Anti-SRP patients harbour more severe muscle weakness and atrophy with severe muscle damage on magnetic resonance imaging study. Approximately 10-20% of anti-SRP patients develop extramuscular symptoms, especially lung interstitial disease. Conversely, anti-HMGCR patients are often associated with statin exposure. In both cases, patients have a poor outcome with frequent relapse and the use of combined immunotherapy. Of note, various data suggest a direct pathogenic role of these antibodies reinforcing the interest in targeted therapeutic strategy.

Anti-HMGCR Myopathy

Anti-HMGCR myopathy was first recognized and characterized in patients with a history of statin exposure and immune-mediated necrotizing myopathy. After the discovery of anti-HMGCR autoantibodies, several international groups identified and characterized more patients, expanding the phenotypic spectrum of this disease to include pediatric patients and young adults without statin exposure and those with a chronic myopathy resembling limb-girdle muscular dystrophy. We provide a summary of clinical findings, pathologic features, muscle imaging, and immunogenetic risk factors of the disease. We also discuss the current treatment strategies and approaches to monitoring the therapeutic response. Lastly, we briefly summarize the current understanding of the pathophysiology of the disease and postulate a model for autoimmunity initiation and propagation in this disease.

Autoimmunity in 2016

The number of peer-reviewed articles published during the 2016 solar year and retrieved using the "autoimmunity" key word remained stable while gaining a minimal edge among the immunology articles. Nonetheless, the quality of the publications has been rising significantly and, importantly, acquisitions have become available through scientific journals dedicated to immunology or autoimmunity. Major discoveries have been made in the fields of systemic lupus erythematosus, rheumatoid arthritis, autoimmunity of the central nervous system, vasculitis, and seronegative spondyloarthrithritides. Selected examples include the role of IL17-related genes and long noncoding RNAs in systemic lupus erythematosus or the effects of anti-pentraxin 3 (PTX3) in the treatment of this paradigmatic autoimmune condition. In the case of rheumatoid arthritis, there have been reports of the role of induced regulatory T cells (iTregs) or fibrocytes and T cell interactions with exciting implications. The large number of studies dealing with neuroimmunology pointed to Th17 cells, CD56(bright) NK cells, and low-level TLR2 ligands as involved in multiple sclerosis, along with a high salt intake or the micriobiome-derived Lipid 654. Lastly, we focused on the rare vasculitides to which numerous studies were devoted and suggested that unsuspected cell populations, including monocytes, mucosal-associated invariant T cells, and innate lymphoid cells, may be crucial to ANCA-associated manifestations. This brief and arbitrary discussion of the findings published in 2016 is representative of a promising background for developments that will enormously impact the work of laboratory scientists and physicians at an exponential rate.

Immune-Mediated Necrotizing Myopathy

PURPOSE OF REVIEW

Immune-mediated necrotizing myopathy (IMNM) is a type of autoimmune myopathy characterized by relatively severe proximal weakness, myofiber necrosis with minimal inflammatory cell infiltrate on muscle biopsy, and infrequent extra-muscular involvement. Here, we will review the characteristics of patients with IMNM.

RECENT FINDINGS

Anti-signal recognition particle (SRP) and anti-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) autoantibodies are closely associated with IMNM and define unique subtypes of patients. Importantly, the new European Neuromuscular Centre criteria recognize anti-SRP myopathy, anti-HMGCR myopathy, and autoantibody-negative IMNM as three distinct subtypes of IMNM. Anti-SRP myopathy patients have more severe muscle involvement, have more common extra-muscular features, and may respond best to immunosuppressive regimens that include rituximab. In contrast, anti-HMGCR myopathy is often associated with statin exposure and intravenous immunoglobulin treatment may be an effective treatment, even as monotherapy. Both anti-SRP and anti-HMGCR myopathy tend to be most severe in younger patients. Furthermore, children with these forms of IMNM may present with dystrophy-like features which are potentially reversible with immunosuppressant treatment. IMNM patients with either autoantibody may experience fatty replacement of muscle soon after disease onset, suggesting that intense and early immunosuppressant therapy may provide the best chance to avoid long-term disability. IMNM is composed of anti-SRP myopathy, anti-HMGCR myopathy, and autoantibody-negative IMNM. Both anti-SRP and anti-HMGCR myopathy can cause severe weakness, especially in younger patients. Anti-SRP myopathy patients tend to have the most severe weakness and most prevalent extra-muscular features. Autoantibody-negative IMNM remains poorly described.

Bench to bedside review of myositis autoantibodies

Idiopathic inflammatory myopathies represent a heterogeneous group of autoimmune diseases with systemic involvement. Even though numerous specific autoantibodies have been recognized, they have not been included, with the only exception of anti-Jo-1, into the 2017 Classification Criteria, thus perpetuating a clinical-serologic gap. The lack of homogeneous grouping based on the antibody profile deeply impacts the diagnostic approach, therapeutic choices and prognostic stratification of these patients. This review is intended to highlight the comprehensive scenario regarding myositis-related autoantibodies, from the molecular characterization and biological significance to target antigens, from the detection tools, with a special focus on immunofluorescence patterns on HEp-2 cells, to their relative prevalence and ethnic diversity, from the clinical presentation to prognosis. If, on the one hand, a notable body of literature is present, on the other data are fragmented, retrospectively based and collected from small case series, so that they do not sufficiently support the decision-making process (i.e. therapeutic approach) into the clinics.

Statin-induced myalgia and myositis: an update on pathogenesis and clinical recommendations

INTRODUCTION

Musculoskeletal manifestations are well-recognized side effects of treatment with statins. New advances in this field have appeared in recent years. This review focuses on the diagnosis of these conditions and their underlying pathogenesis, in particular immune-mediated necrotizing myopathy. Areas covered: Clinical phenotypes including rhabdomyolysis, myalgia and/or mild hyperCKemia, self-limited toxin statin myopathy, and immune-mediated necrotizing myopathy are herein described. Therapeutic recommendations and a diagnostic algorithm in statin-associated myopathy are also proposed. The etiology and pathogenesis of statin-induced myopathy has mainly focused on the anti-HMGCR antibodies and the responsibility of the immune-mediated necrotizing myopathy is discussed. The fact that patients who have not been exposed to statins may develop statin-associated autoimmune myopathy with anti-HMGCR antibodies is also addressed. The literature search strategy included terms identified by searches of PubMed between 1969 and December 2017. The search terms 'myositis', 'statin-induced autoimmune myopathy', 'immune-mediate necrotizing myopathy', 'statins', 'muscular manifestations', and 'anti-HMGCR antibodies' were used. Expert commentary: Full characterization of the known phenotypes of statin toxicity and the specific role of the anti-HMGCR in those exposed and not exposed (i.e. juvenile forms) to statins and in some types of neoplasms is of paramount relevance.

Statin-associated immune-mediated myopathy: biology and clinical implications

PURPOSE OF REVIEW

In the last 6 years, our understanding of statin-associated myopathy expanded to include not only a toxic myopathy with limited and reversible side-effects but also an autoimmune variety in which statins likely induce an autoimmune myopathy that is both associated with a specific autoantibody and responsive to immunosuppression and immune modulation. This review widens the reader's understanding of statin myopathy to include an autoimmune process.

RECENT FINDINGS

Statin-associated immune-mediated myopathy provides an example of an environmental trigger (statins) directly implicated in an autoimmune disease associated with a genetic predisposition as well as potential risk factors including concomitant diseases and specific statins. Given a median exposure to statins of 38 months, providers should be aware that anti-3-hydroxy-3-methyl-glutaryl-coenzyme A reductase (HMGCR) myopathy may occur even after several years of statin exposure.

SUMMARY

It is important for the reader to understand the clinical presentation of statin-associated immune-mediated myopathy and the difference in its clinical presentation to that of statins as direct myotoxins. Prompt recognition of such an entity allows the clinician to immediately stop the offending agent if it has not already been discontinued as well as to recognize that statin rechallenge is not a likely option, and that prompt treatment with immunosuppression and/or immunomodulation is usually of enormous benefit to the patient in restoring muscle strength and physical function. VIDEO ABSTRACT.