Clinical and persistent remission in anti-HMGCR immune-mediated necrotizing myopathy to a single cycle of rituximab - a case-based review.

Anti-HMGCR myopathy is an increasingly recognized immune-mediated necrotizing myopathy. However, there are currently no evidence-based treatments available, so case reports and clinical experience are used to guide current management. We report a case of a 49-year-old man, treated with atorvastatin, who presented to the emergency department with progressive proximal muscle weakness. Anti-HMGCR antibodies were detected, and muscle biopsy revealed necrotizing myopathy. Initially, therapy with high-dose glucocorticoids and methotrexate was started, but 12 weeks later, the patient developed clinical deterioration with dysphagia. Then, he was successfully treated with one cycle of rituximab along with physical therapy. The use of rituximab in immune-mediated necrotizing myopathy has been heterogeneously described in the literature but mostly in case reports. The European Neuromuscular Centre working group recommends the use of rituximab in refractory cases. However, some studies highlight the importance of early and aggressive treatment for this disease. Clinical prospective studies are necessary to make proper evidence-based recommendations.

Association of anti-HMGCR antibodies of the IgM isotype with refractory immune-mediated necrotizing myopathy.

OBJECTIVE: Anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) autoantibodies are one of the myositis-specific antibodies which is associated with immune-mediated necrotizing myopathy (IMNM). However, the relationship between anti-HMGCR isotypes and prognosis has not yet been fully investigated. This study was conducted to gain insight into the association between anti-HMGCR isotypes and clinical, and prognosis in IMNM patients who were positive for anti-HMGCR antibodies. METHODS: Levels of anti-HMGCR isotypes (IgG, IgA and IgM) were assessed by enzyme-linked immunosorbent assay (ELISA) in 123 consecutive serum samples obtained from 71 patients who were positive for anti-HMGCR IgG at baseline. Disease activity was assessed by manual muscle testing (MMT) 8, Physician's Global Assessment (PGA) visual analog scale (VAS), and muscle VAS. RESULTS: Baseline anti-HMGCR IgG levels were correlated with PGA VAS (r = 0.24; p = 0.04), muscle VAS (r = 0.32; p < 0.01), and MMT8(r=-0.24; p = 0.04), and baseline anti-HMGCR IgM levels were positively correlated with PGA VAS (r = 0.27, p = 0.02), muscle VAS (r = 0.24, p = 0.04). Anti-HMGCR IgM positive patients had a lower age of onset [29(25,46) vs. 51(33,65), p = 0.006], and a higher proportion of neck weakness (63.5% vs. 34.6%, p = 0.031) compared with anti-HMGCR IgM negative patients. Longitudinal analysis showed that the changes in anti-HMGCR IgG levels were correlated with the changes in the PGA VAS (ß = 3.830; p < 0.0001), muscle VAS (ß = 2.893; p < 0.0001), MMT8 (ß=-19.368; p < 0.0001), and creatine kinase (CK) levels (ß = 3900.05, p < 0.0001). Anti-HMGCR IgM levels were weakly correlated with anti-HMGCR IgA levels at baseline (r = 0.33, p < 0.01), and the variations in anti-HMGCR IgA levels were correlated with the changes in anti-HMGCR IgM levels during follow-up (ß = 0.885; p < 0.0001). There were more patients with anti-HMGCR IgM who showed a refractory course than those who were with anti-HMGCR IgM negative (polycyclic course: 40% vs. 25%; chronic continuous course: 46.7% vs. 20.5%, p = 0.018). CONCLUSION: In anti-HMGCR IgG-positive IMNM patients, the levels of anti-HMGCR IgG are associated with disease activity, and anti-HMGCR IgM is associated with refractory outcome and poor prognosis.

Absence of Pathogenic Mutations and Strong Association With HLA-DRB1*11:01 in Statin-Naïve Early-Onset Anti-HMGCR Necrotizing Myopathy.

BACKGROUND AND OBJECTIVES: Immune-mediated necrotizing myopathy (IMNM) caused by antibodies against 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR) is an inflammatory myopathy that has been epidemiologically correlated with previous statin exposure. We characterized in detail a series of 11 young statin-naïve patients experiencing a chronic disease course mimicking a limb-girdle muscular dystrophy. With the hypothesis that HMGCR upregulation may increase immunogenicity and trigger the production of autoantibodies, our aim was to expand pathophysiologic knowledge of this distinct phenotype. METHODS: Clinical and epidemiologic data, autoantibody titers, creatine kinase (CK) levels, response to treatment, muscle imaging, and muscle biopsies were assessed. HMGCR expression in patients' muscle was assessed by incubating sections of affected patients with purified anti-HMGCR+ serum. Whole-exome sequencing (WES) with a special focus on cholesterol biosynthesis-related genes and high-resolution human leukocyte antigen (HLA) typing were performed. RESULTS: Patients, aged 3-25 years and mostly female (90.9%), presented with subacute proximal weakness progressing over many years and high CK levels (>1,000 U/L). Diagnostic delay ranged from 3 to 27 years. WES did not reveal any pathogenic variants. HLA-DRB1*11:01 carrier frequency was 60%, a significantly higher proportion than in the control population. No upregulation or mislocalization of the enzyme in statin-exposed or statin-naïve anti-HMGCR+ patients was observed, compared with controls. DISCUSSION: WES of a cohort of patients with dystrophy-like anti-HMGCR IMNM did not reveal any common rare variants of any gene, including cholesterol biosynthesis-related genes. HLA analysis showed a strong association with HLA-DRB1*11:01, previously mostly described in statin-exposed adult patients; consequently, a common immunogenic predisposition should be suspected, irrespective of statin exposure. Moreover, we were unable to conclusively demonstrate muscle upregulation/mislocalization of HMGCR in IMNM, whether or not driven by statins.

Benefits of Early Versus Late Initiation of Intravenous Immunoglobulin in the Treatment of Patients With Anti-3-Hydroxy-3-Methylglutaryl-Coenzyme A Reductase Immune-Mediated Necrotizing Myopathy.

OBJECTIVE: No clinical trials have been conducted to establish optimal and effective treatment in patients with immune-mediated necrotizing myopathy (IMNM), which can have a refractory course with increased morbidity from permanent muscle damage, especially in patients who experience delay in diagnosis and treatment. A subset of autoimmune necrotizing myopathy is associated with antibodies against 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR). Treatment involves withdrawing statins and using a combination of immunosuppressant and immunomodulatory treatment. Our study aims to provide longitudinally collected data on outcomes of early versus late initiation of intravenous Ig (IVIG) using our myositis center cohort of patients with anti-HMGCR IMNM. METHODS: We conducted a retrospective chart review of 31 adult patients of the Oregon Health and Science University Myositis Center who were diagnosed with anti-HMGCR IMNM from September 2016 through October 2022 and reviewed physical examination, serologic laboratory data, and their treatment including prednisone reception as well as treatment response at 0 (the evaluation immediately before IVIG initiation), 3, 6, and 12 months on treatment. We divided this cohort into those who received IVIG at or before six months after receiving the diagnosis of anti-HMGCR IMNM and refer this as the cohort with nondelayed treatment, and those who received IVIG after six months following their diagnosis, which we referred to as the cohort with delayed treatment. Diagnosis of anti-HMGCR IMNM was defined as per the 2016 European Neuromuscular Centre criteria as having all three of elevated serum creatine kinase (CK), proximal muscle weakness, and anti-HMGCR antibodies. We evaluated the response to treatment by using a limited total improvement score (TIS) as per 2016 American College of Rheumatology/EULAR myositis response criteria. RESULTS: Among the 31 total patients, 19 were included within the cohort with nondelayed treatment, and 12 within the cohort with delayed treatment. The two cohorts had a comparable amount of time between the onset of symptoms and diagnosis; however, the cohort with delayed treatment had a significantly longer time between diagnosis and IVIG treatment (P < 0.001). At disease onset, cohorts had a comparable serum CK (P > 0.999), but patients with delayed treatment had an expected lower serum CK (P = 0.016) at the 0-month time point. At the 0-month time point, nine of the patients with nondelayed treatment (47%) required the use of a walker or wheelchair, whereas eight of the cohort with delayed treatment (66%) did. Patients who received nondelayed treatment demonstrated significant improvement in manual muscle testing 8 at the 12-month intervals (P < 0.001). Average serum CK values of all patients measured at the 3, 6, and 12 months did not significantly differ between the groups with nondelayed and delayed treatment. TIS improved more in the group with nondelayed treatment than in the group with delayed treatment (P = 0.002 at 3 months, P = 0.019 at 6 months, and P = 0.001 at 12 months). Seven patients in the group with delayed treatment had permanent residual muscle weakness requiring walker or wheelchair use at 12 months, whereas none of the patients in the group with nondelayed treatment did. CONCLUSION: Though our results have limitations, they contribute to a growing body of evidence that suggests that IVIG may prove to be a valuable addition to an early and aggressive induction regimen in patients afflicted by anti-HMGCRIMNM, particularly those with moderate to severe weakness requiring the use of a wheelchair or walking aids. Delay in IVIG treatment may lead to the development of permanent residual weakness and long-term disability.

Ophthalmoparesis as an unusual manifestation of anti-3­hydroxy-3-methyl-glutaryl-coenzyme A reductase antibody-associated myopathies.

We describe two anti-3­hydroxy-3-methyl-glutaryl-coenzyme A reductase (HMGCR) antibody-positive patients with treatment-responsive ophthalmoparesis. Patient 1 was a 53-year-old male with progressive proximal limb weakness, dysphagia, ptosis, and diplopia over 6 weeks and creatine kinase (CK) of 3,512 units/L. Patient 2 was a 55-year-old female with progressive proximal weakness, dysarthria, ptosis, diplopia, and dyspnea over 2 weeks with CK of 31,998 units/L. Both patients had normal thyroid studies and repetitive nerve stimulation, myopathic electromyography with fibrillation potentials, magnetic resonance imaging demonstrating abnormal enhancement of extraocular muscles, muscle biopsy showing necrotic myofibers, and positive anti-HMGCR antibodies. Patient 1 also had weakly positive anti-PM/Scl antibodies. Immunomodulatory therapies led to resolution of oculobulbar weakness and normalization of CK levels in both patients, while limb weakness resolved completely in patient 1 and partially in patient 2. These cases expand the phenotypic spectrum of anti-HMGCR antibody-associated myopathies to include subacute ophthalmoparesis with limb-girdle weakness and markedly elevated CK.

Anti-HMGCR myopathy: Diversity of clinical presentations in a national cohort in New Zealand.

AIMS: We describe the varied clinical presentations, barriers in diagnosis and outcomes of anti-HMGCR myopathy in a large national cohort. METHODS: Adults found positive for serum anti-HMGCR autoantibodies via line blot or enzyme-immunoassay followed by immunoprecipitation were included in the study. RESULTS: Of 75 patients identified, the records of 72 (96 %) described weakness as the presenting symptom. The records of 65 gave a reliable description of proximal weakness. In 22/65 (33.8 %) the weakness was described as predominantly or solely lower limb weakness. Forty-five of 75 (60 %) presented with a subacute onset (duration of symptoms >4 weeks -≤6 months), whilst 22/75 (29.3 %) presented with a more indolent chronic onset (duration of symptoms >6 months). Eighteen of 75 (24 %) suffered falls and 2/75 (2.7 %) had "general decline". In three patients no weakness was described: two presented with myalgia and one with a skin rash characterized as Jessner lymphocytic skin rash. Median creatine kinase at presentation was 7337 U/L (range 1050-25,500). Muscle biopsy was performed in 38 (50.7 %). Associated malignancy was infrequent. Four patients recovered without immunosuppression. Five-year and 10-year survival was 92.7 % (95 % CI 80.6-97.4 %), and 82.5 % (95 % CI 61.2-92.8 %) respectively. CONCLUSION: Recurrent falls, a long prodrome and dominant lower limb proximal weakness were common in this anti-HMGCR myopathy cohort. These features overlap with frailty syndrome and sporadic inclusion body myositis emphasizing the importance of considering anti-HMGCR myopathy in that clinical context. A minority of patients recover after statin withdrawal alone.

Successful treatment with reduced oral steroid dosage in an 81-year-old woman with statin-induced anti-HMGCR immune-mediated necrotizing myopathy.

An 81-year-old woman presented with statin-induced anti-HMGCR immune-mediated necrotizing myopathy. Treatment was successful without complications with a reduced oral steroid dosage from the current consensus for all ages and backgrounds. This case suggests the importance of early diagnosis and the possibility of steroid dosage adjustment considering the patient's age, disease severity, and comorbidities.

[Immune-Mediated Necrotizing Myopathy].

Immune-mediated necrotizing myopathy (IMNM) is a form of autoimmune myositis characterized by the presence of necrotic and regenerating process as a major finding in the muscle. Anti-SRP and anti-HMGCR have been identified as IMNM-specific autoantibodies. Patients with this disease often present with severe muscle weakness and markedly elevated serum creatine kinase (CK) levels. Differentiation from muscular dystrophy is challenging in certain cases. When patients meet the condition "subacute onset", "hyperCKemia over 1000 IU/L", and "clinical diagnosis of muscular dystrophy lacking molecular diagnosis", the possibility of IMNM should be considered. Autoantibody measurement, including of anti-SRP and HMGCR antibodies, is recommended. Treatment with corticosteroid in combination with immunosuppressants, intravenous immunoglobulin, and rituximab can be performed.

Management of immune-mediated necrotizing myopathy.

The immune-mediated necrotizing myopathies (IMNM) are autoimmune myositides clinically characterized by proximal predominant weakness and elevated creatine kinase (CK). They may be associated with autoantibodies (anti-HMGCR, anti-SRP), triggered by statin use (e.g., anti-HMGCR myopathy), associated with cancer, or may be idiopathic. Immunotherapy is required to improve strength and decrease the CK level, but no therapies are currently approved by the U.S. Food and Drug Administration for the treatment of IMNM. The optimal treatment strategy for IMNM is currently unknown and wide practice variation exists in the management of this condition. However, observational studies and expert opinion suggest that certain therapies may be more effective for the different serological subtypes of IMNM. HMGCR IMNM often responds favorably to intravenous immunoglobulin (IVIG) even as monotherapy. Signal recognition peptide and seronegative IMNM typically require combination immunotherapy, most often consisting of an oral immunosuppressant, corticosteroids, and IVIG or rituximab. Patients often remain on immunotherapy for years and relapse is common during tapering of immunotherapy. Further studies are needed to guide the optimal management of these patients.

Atypical skin conditions of the neck and back as a dermal manifestation of anti-HMGCR antibody-positive myopathy.

BACKGROUND: Immune-mediated necrotizing myopathy (IMNM) is an idiopathic inflammatory myopathy (IIM). Though patients with IMNM were not considered to show skin rash, several reports have showed atypical skin conditions in patients with anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) antibody-positive IMNM (HMGCR-IMNM). The incidence and phenotype of skin conditions in patients with HMGCR-IMNM are not fully known. RESULTS: Among the 100 IIM patients diagnosed from April 2015 through August 2022, 34 (34%) presented some form of skin condition, with 27 having typical skin rashes; this included 13 patients with dermatomyositis (DM), 8 with anti-synthetase syndrome (ASS), and 6 with IMNM. Meanwhile, 8 of 19 patients with HMGCR-IMNM (42%) presented atypical skin lesions, but no patients with other IIMs did (p < 0.001). Skin eruption with ash-like scales was observed in four HMGCR-IMNM patients, and non-scaly red patches and lumps in the other four patients; accordingly, their skin manifestations were considered as other dermal diseases except for IIM. However, skin and muscle biopsies revealed the atypical skin conditions of patients with HMGCR-IMNM to have the same pathological background, formed by Bcl-2-positive lymphocyte infiltrations. CONCLUSIONS: HMGCR-IMNM patients frequently have atypical skin conditions of the neck and back. Skin biopsy specimens from these lesions showed the same Bcl-2-positive lymphocytic infiltrations as muscle biopsy specimens regardless of the different gross dermal findings. Thus, such atypical skin conditions may be suggestive for HMGCR-IMNM.

Six Years Follow-Up of an 11-Year-Old Girl with Anti-HMGCR Myopathy.

Anti-HMGCR myopathy is decribed as an immune-mediated necrotizing myopathy which is characterised by subacute, progressive proximal muscle weakness and elevated creatine kinase (CK) level. In pediatric population, anti-HMGCR myopathy has been reported solely as small case reports, albeit rare. Although treatment consensus has not yet been established, proper treatment with several immunomodulators to include IVIg can show remarkable improvement. We report an 11-year-old-girl diagnosed with anti-HMGCR myopathy with 6 years of follow-up.

Causal modulation of lipid metabolism may shape the inflammatory microenvironment and potentially augment immunotherapy: a comprehensive genetic landscape revealed by Mendelian randomization analysis.

Previous observational and experimental studies have suggested a relationship between statin treatments and the augmentation of immunotherapy effects; however, the causal role of statin usage in promoting antitumor immunity remains largely unexplored. Utilizing large-scale genome-wide association studies, we conducted a Mendelian Randomization (MR) analysis to examine the association between genetically proxied inhibition of the gene for 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR), a specific target of statins, and 524 immunotherapy-related profiles, encompassing immune cells, inflammatory cytokines, immune checkpoints, and gut microbiota. Our findings indicated a suggestive association between statin therapy and proinflammatory as well as antitumor effects; notably, inhibition of HMGCR demonstrated a robust link with increased susceptibility of various immune cell types, including basophil cells, white blood cells, eosinophil cells, neutrophil cells, activated CD8+ T cells, dendritic cells, and natural killer cells; furthermore, a causal relationship was observed between statin use and a decrease in terminal CD8+ T cells, granulocytes, monocytes, and myeloid-derived suppressor cells; genetically proxied statin usage was also significantly associated with elevated levels of proinflammatory cytokines and immunotherapy-related gut microbiota; importantly, the potential inhibition of HMGCR in influencing the response to immunotherapy was confirmed in the real-world cohorts. This study provides novel insights into the regulatory role of HMGCR inhibition in antitumor immunity, suggesting that strategies targeting HMGCR or lipid regulation may hold therapeutic potential for enhancing the efficacy of immunotherapy.

Mushroom supplements triggering a flare of HMGCR immune mediated necrotising myopathy.

Hydroxyl-methyl-glutaryl-Co-A reductase (HMGCR) immune mediated necrotising myopathy (IMNM) is a rare autoimmune myositis that is thought to be triggered by statins and responds to immunomodulation. We report a case of a woman in her 30s with HMGCR IMNM without a history of statin exposure who had a clear flare of her myositis after beginning mushroom supplements. Mushrooms are natural HMGCR inhibitors, and this is the first case to demonstrate a flare triggered by mushrooms in a patient with known HMGCR IMNM. This case highlights the importance of reviewing diet and supplements in patients with IMNM. It also emphasises the importance of strict statin avoidance for patients with IMNM even when the myositis is under good control.

Anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase antibodies: incidence using different testing criteria, and case series.

OBJECTIVES: To estimate the incidence of anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) antibodies utilising different testing criteria, and review the clinical details of a series of patients with associated autoimmune myopathy. METHODS: The incidence of anti-HMGCR antibodies in 2019 from 3 groups, South West London, Berkshire/Surrey and Southampton, were compared in the adult population. Anti-HMGCR antibodies were measured by commercial chemiluminescent and immunodot assays. The case notes of patients with anti-HMGCR antibodies were reviewed for the case series. RESULTS: The estimated incidence of anti-HMGCR antibodies in the first 2 groups was 1.94 per million adults per year, and in the third group 10.3 per million adults per year. In the first 2 groups the test criteria restricted analysis to specific clinician request for anti-HMGCR. In the third group test criteria included cases with less specific clinical features or a cytoplasmic indirect immunofluorescence anti-nuclear antibody pattern. The latter strategy had a positive predictive value of 66.1% for anti-HMGCR associated myopathy. A case series of 27 patients with anti-HMGCR antibodies revealed 19 with myopathy, oesophageal involvement in 26% and median peak CK 8000 IU/L. Response to treatment, including intravenous immunoglobulin, was good with CK normalising after median 5.5 months. In 8 cases there was no evidence of autoimmune muscle disease, 7 not statin exposed. CONCLUSIONS: Varying criteria result in a 5-fold difference in estimated incidence of anti-HMGCR antibodies, revealing positive cases without evidence of myopathy. Patients with anti-HMGCR myopathy respond well to immune suppression, supporting wider testing for these antibodies amongst patients with myopathy.

The Significance of Autoantibodies in Juvenile Dermatomyositis.

Juvenile dermatomyositis is a chronic and rare autoimmune disorder classified into the spectrum of idiopathic inflammatory myopathies. Although this entity is mainly characterized by the presence of pathognomonic cutaneous lesions and proximal muscle weakness, the clinical manifestation can be highly heterogeneous; thus, diagnosis might be challenging. Current treatment recommendations for juvenile dermatomyositis, based mainly upon case series, include the use of corticosteroids, immunomodulatory, and immunosuppressive agents. Recently, several specific autoantibodies have been shown to be associated with distinct clinical phenotypes of classic dermatomyositis. There is a need to further evaluate their relevance in the formation of various clinical features. Furthermore, while providing more personalized treatment strategies, one should consider diversity of autoantibody-related subgroups of juvenile dermatomyositis.

Pathology Features of Immune and Inflammatory Myopathies, Including a Polymyositis Pattern, Relate Strongly to Serum Autoantibodies.

We asked whether myopathology features of immune or inflammatory myopathies (IIM), without reference to clinical or laboratory attributes, correlate with serum autoantibodies. Retrospective study included 148 muscle biopsies with: B-cell inflammatory foci (BIM), myovasculopathy, perimysial pathology (IMPP), myofiber necrosis without perimysial or vessel damage or inflammation (MNec), inflammation and myofiber vacuoles or mitochondrial pathology (IM-VAMP), granulomas, chronic graft-versus-host disease, or none of these criteria. 18 IIM-related serum autoantibodies were tested. Strong associations between myopathology and autoantibodies included: BIM with PM/Scl-100 (63%; odds ratio [OR] = 72); myovasculopathies with TIF1-γ or NXP2 (70%; OR = 72); IMPP with Jo-1 (33%; OR = 28); MNec with SRP54 (23%; OR = 37); IM-VAMP with NT5C1a (95%; OR = 83). Hydroxymethylglutaryl-CoA reductase (HMGCR) antibodies related to presence of myofiber necrosis across all groups (82%; OR = 9), but not to one IIM pathology group. Our results validate characterizations of IIM by myopathology features, showing strong associations with some serum autoantibodies, another objective IIM-related marker. BIM with PM/Scl-100 antibodies can be described pathologically as polymyositis. Tif1-γ and NXP2 antibodies are both common in myovasculopathies. HMGCR antibodies associate with myofiber necrosis, but not one IIM pathology subtype. Relative association strengths of IIM-related autoantibodies to IIM myopathology features versus clinical characteristics require further study.

Cutaneous involvement in anti-HMGCR positive necrotizing myopathy.

OBJECTIVE: Anti-3-Hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) positive immune-mediated necrotizing myopathy (IMNM) is a rare disease. It is induced by exogenous substances, most often by statins. Little is known about cutaneous manifestations of HMGCR positive IMNM and about HMGCR antibody positivity in other diseases. METHODS: The characteristics of patients with anti-HMGCR autoantibodies measured at our laboratory between January 2012 and September 2020 were studied. Characteristics of patients with IMNM were compared to those patients with positive antibodies but without muscle involvement. Associations of IMNM with other organ involvements were searched for. RESULTS: Of the 32 patients studied, 23 showed characteristics of IMNM, 9 did not fulfill current classification criteria but most showed signs of connective tissue diseases. Patients with IMNM were older (66 and 35 years, respectively; 0.92 (0.73-0.98); p < 0.001), had more frequent statin exposure (87% and 33%, respectively; 0.84 (0.61-0.94); p = 0.005) and higher mean peak CK (8717U/l and 329U/l, respectively; 1.0 (0.85-1.0); p < 0.001). 13/23 (56%) of IMNM patients showed cutaneous lesions; none of the patients suffered from cancer; only three IMNM patients showed drug-free complete remission. Incidence of IMNM in the catchment area of our center is at least 2.7/Mio/year. CONCLUSION: Cutaneous lesions were found to be more frequent in anti-HMRCR positive IMNM than previously reported. Titer of anti-HMGCR antibodies and CK levels were significantly higher in IMNM than in other autoimmune connective tissue diseases. The data support the hypothesis of an antigen-driven response in IMNM, and suggests an activation of autoreactive B-lymphocytes in non-IMNM patients.

[A 81-year old man of anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase antibody-positive myopathy associated with lung adenocarcinoma cancer].

An 81-year-old man, who had no history of taking statins, developed progressive muscle weakness of the limbs and dysphagia. Laboratory tests showed a high level of CK and positivity for serum 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) antibodies. Tests for other autoantibodies to ARS and SRP were negative. A pathological analysis of the left biceps muscle revealed numerous necrotic and regenerated fibers with macrophage infiltration and deposition of C5b-9 complement in and around the myofibers. Chest CT showed a nodular shadow, which was suspected to be lung cancer, in the upper left lobe. A pathological analysis of a transbronchial lung biopsy specimen revealed lung adenocarcinoma with high level of HMGCR. He was diagnosed with HMGCR necrotizing myopathy associated with lung cancer, and both his muscle strength and dysphagia improved after three treatments with intravenous immunoglobulin (IVIg). He did not undergo surgery or radiation therapy because of interstitial pneumonia. This case suggests that a paraneoplastic mechanism caused the production of HMGCR antibodies, leading to myositis in this patient. Treatment with IVIg can be effective for patients with HMGCR antibody-positive paraneoplastic necrotizing myopathy that is refractory to corticosteroid therapy.