Paraneoplastic Inflammatory Myositis False-positive for Anti-aminoacyl-tRNA synthetase Antibody Successfully Ameliorated by Immunosuppressive Therapy

Abstract

We herein report a 60-year-old woman with anti-aminoacyl-tRNA synthetase (ARS) antibody-false-positive paraneoplastic polymyositis complicated with ovarian carcinoma, which was promptly ameliorated by immunosuppressive therapy, including glucocorticoids (GCs), before treatment against malignancy. The patient was admitted to our hospital because of rapidly progressive muscular weakness of the neck and both limbs over three weeks. Upon a detailed examination, the patient tested positive for anti-ARS antibodies by an enzyme-linked immunosorbent assay (ELISA), which were later determined to be false positives, as confirmed by immunoblotting and immunoprecipitation. She was strongly suspected to have ovarian carcinoma and pulmonary metastasis. A biopsy of her muscle revealed myositis, mainly with CD68⁺ macrophage infiltration and slightly with CD8⁺ T cells. High-dose GC therapy was introduced as remission induction therapy before intervention for ovarian carcinoma (later revealed as clear cell carcinoma), which showed prompt efficacy for her laboratory findings and then gradually improved her symptoms thereafter. It is speculated that the unusual immunological condition of cancer-associated myositis, characterized by enhanced antibody production, including non-specific autoantibodies such as anti-ARS antibodies, may influence the treatment response. Therefore, a detailed investigation of muscle pathology and the specificity of anti-ARS antibodies could help clarify the precise pathogenesis of inflammatory myositis, even when myositis and anti-ARS antibodies detected by an ELISA are simultaneously detected in patients with malignancy.

Introduction

Polymyositis (PM) and dermatomyositis (DM) are systemic autoimmune diseases that have recently been defined as subgroups of idiopathic inflammatory myopathies (IIMs). Among the clinical types of PM/DM stratified according to myositis-specific autoantibodies (MSAs), anti-transcriptional intermediary factor (TIF) 1-γ antibody-positive DM is known to frequently complicate malignancy (1). However, whether or not anti-aminoacyl-tRNA synthetase (ARS) antibody-positive PM/DM is related to the coexistence of malignancy remains controversial (2).

According to previous studies, cancer-associated myopathy (CAM) as a part of PM/DM is generally considered refractory to conventional immunosuppressive therapies in the absence of intervention against malignant tumors (3).

We herein report a case of anti-ARS antibody-false-positive active inflammatory myositis complicated by ovarian carcinoma, in which the myositis was successfully ameliorated through immunosuppressive therapy before specific intervention for the malignancy.

Case Report

A 60-year-old woman with no significant medical history developed pain in her shoulder, elbows, and legs, and myalgia without any apparent cause. Due to the persistent nature of myalgia, she visited an orthopedic specialist who discovered an elevated creatinine kinase (CK) level of 1,950 IU/L. In addition, she developed a fever of approximately 38.0°C and dysphagia, with worsening myalgia in both limbs. Three weeks after the appearance of the initial symptoms, the patient was referred to our university hospital. She had no significant abnormalities in her vital signs other than a low-grade fever of 37.3°C. A physical examination revealed a manual muscle test (MMT) score of 2 for the neck flexor muscles and 4-/4- for the proximal muscles in both limbs with tenderness. She had difficulty sitting from a lying position on the bed. However, she had no specific skin lesions, including facial rash, heliotrope rash, Gottron's sign, or mechanic's hand. Blood chemistry revealed elevated levels of CK at (2,758 IU/L), aldolase (111 U/L), and C-reactive protein (4.18 mg/dL). Immunological tests showed a negative anti-nuclear antibody test but a positive cytoplasmic pattern by indirect immunofluorescent staining, an anti-ARS antibody index of 96.2 (MESACUP™ anti-ARS test), and a negative anti-Jo-1 antibody result by an enzyme-linked immunosorbent assay (ELISA) (Table).

Table.

Laboratory Data on Admission.

(Urine)			(Biochemistry)			(Immunity)
Specific gravity	1.022		TP	6.9	g/dL	Ferritin	274	ng/mL	Anti-TIF1-γ	<5	index
pH	5.5		Alb	2.4	g/dL	CRP	4.18	mg/dL	Anti-Mi-2	<5	index
UP	(2+)		Tbil	0.4	mg/dL	IgG	2,003	mg/dL	Anti-MDA5	<4	index
UG	(-)		BUN	10.7	mg/dL	IgA	382	mg/dL	Anti-ARS (ELISA)	96.2	index
UB	(-)		Cr	0.44	mg/dL	IgM	182	mg/dL	Anti-Jo-1 (IB)	Negative
(Complete blood count)			AST	248	U/L	C3	125	mg/dL	Anti-PL-7 (IB)	Negative
WBC	7,810	/μL	ALT	220	U/L	CH50	37.7	U/mL	Anti-PL-12 (IB)	Negative
Neut	85.6	%	ALP	89	U/L	ANA	<40	(cytoplasmic+)	Anti-EJ (IB)	Negative
Lymp	11.8	%	LDH	601	U/L	MPO-ANCA	(-)		Anti-KS (IP)	Negative
Eosino	0.8	%	CK	2,758	IU/L	PR3-ANCA	(-)		Anti-OJ (IB)	Negative
Mono	1.7	%	Na	135	mEq/L	RF	<3	IU/mL	Anti-Ku (IB)	Negative
Hb	11.8	g/dL	K	4.8	mEq/L	Anti-CCP	<0.6	U/mL	Anti-SRP (IB)	Negative
Plt	15.2×104	/μL	Cl	98	mEq/L				Anti-PM-Scl-75 (IB)	Negative
									Anti-PM-Scl-100 (IB)	Negative
									Anti-Ro52 (IB)	Negative
									Anti-SRP (ELISA)	<1.0	U/mL
									Anti-HMGCR (ELISA)	<1.0	U/mL

UP: urinary protein, UG: urinary glucose, UB: urinary blood, Neut: neutrophils, Lymp: lymphocytes, Eosino: eosinophils, TP: total protein, Alb: albumin, Tbil: total bilirubin, BUN: blood urea nitrogen, Cr: creatinine, AST: aspartate aminotransferase, ALT: alanine aminotransferase, ALP: alkaline phosphatase, LDH: lactate dehydrogenase, CK: creatine kinase, CRP: C-reactive protein, IgG: immunoglobulin G, IgA: immunoglobulin A, IgM: immunoglobulin M, IgE: immunoglobulin E, CH50: 50% hemolytic unit of complement, ANA: antinuclear antibody, MPO: myeloperoxidase, PR3: proteinase3, ANCA: antineutrophil cytoplasmic antibody, RF: rheumatoid factor, Anti-CCP: anti-cyclic citrullinated peptide antibody, Anti-ARS: anti-aminoacyl-tRNA synthetase antibody, Anti-TIF1-γ: anti-transcription intermediary factor 1-gamma antibody, Anti-MDA5: anti-melanoma differentiation-associated gene 5 antibody, Anti-SRP: anti-signal recognition particle antibody, anti-HMGCR: anti-3-hydroxy-3-methylglutaryl coenzyme A reductase antibody, ELISA: enzyme-linked immunosorbent assay, IB: immunoblot, IP: immunoprecipitation

On T2, short τ inversion recovery of magnetic resonance imaging (MRI) in muscles showed significantly high intensities in the cervical muscles, bilateral deltoids, biceps brachii, triceps brachii, trapezius, latissimus dorsi, gluteus maximus, iliopsoas, quadriceps, biceps, and femoris (Fig. 1). Enhanced computed tomography (CT) revealed a 15-mm nodular lesion in the middle lobe of her right lung with no significant interstitial lesions as well as a 94-mm mass lesion in her pelvis (Fig. 2), and contrast-enhanced MRI also revealed a 94-mm mass lesion in her pelvis, suggesting ovarian carcinoma and its invasion to the uterus (Fig. 3). On ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography/CT, FDG accumulation was found at the site that was supposed to be the uterus with a maximum standardized uptake value (SUVmax) of 9.8 and in the right middle lobe with an SUVmax of 4.3. In addition, a diffuse FDG uptake was observed in the skeletal muscles. To obtain additional information for the definitive diagnosis, we performed a muscle biopsy of the left biceps. A histopathological examination of the biceps muscle revealed some variation in fiber size, slight dense fibers with heterogeneous diameters, and dense infiltration of inflammatory cells. In addition, there was significant necrosis in the muscles but no perifascicular necrosis (Fig. 4A-C). Most of the infiltrating cells were clusters of differentiation (CD) 68⁺ cells (Fig. 4D), suggesting the presence of macrophages, and some of the cells were CD8⁺ T cells (Fig. 4E). Given these findings, along with her clinical manifestations, including the absence of interstitial lung disease, lack of skin lesions, subacute onset of muscle weakness, and macrophage infiltration in the muscle, which are atypical for the clinical phenotype of anti-ARS antibody-positive dermatomyositis or anti-ARS antibody syndrome, we comprehensively diagnosed her with CAM due to highly suspected ovarian, uterine, or lung cancer, even though she met all eight criteria for polymyositis according to the classification guidelines established by the Japan Ministry of Health, Labour and Welfare.

Figure 1.

MRI findings of muscles. Significantly high intensities (white arrows) on T2 short τ inversion recovery in the trapezius (A), latissimus dorsi (B), biceps brachii (C), triceps brachii (D), and biceps femoris (E) muscles.

Figure 2.

Chest and abdominal CT and MRI findings on admission. A 15-mm nodular shadow is observed in the right middle lobe (A). A 94-mm mass was found in the pelvic cavity on CT (B, C) and MRI (D).

Figure 3.

Positron emission tomography-computed tomography (PET-CT) findings. A significant FDG uptake was found in the tumor in the pelvic cavity with a maximum standardized uptake value (SUVmax) of 9.8 (A and C) and in a nodular shadow in the right middle lobe with an SUVmax of 4.3 (B).

Figure 4.

Histopathological findings of muscles. Muscular fibers with massive and diffuse infiltration of inflammatory cells (A-C) mostly consist of CD68⁺macrophages (D) and a few CD8⁺T cells (E), suggesting necrosis and regeneration of muscles, while no perifascicular necrosis or perifascicular atrophy was found.

Since she exhibited progressive muscular weakness due to difficulty swallowing, we initially introduced immunosuppressive therapy with glucocorticoid (GC) pulse therapy, followed by high-dose GC in combination with tacrolimus during the search for malignancy. Six days after the introduction of the initial GC therapy, her CK level decreased to the normal range of 123 IU/L. However, we intensified the treatment with an intravenous infusion of 20 g/day for 5 days of immunoglobulin for her sustained muscular weakness, including persistent severe weakness in her neck flexor muscles, and to facilitate prompt evaluation of malignancy. Ten days after the initial treatment, we began weekly tapering of GC to facilitate surgery for malignancy. After two weeks, MMT improved to 3 in her neck flexor muscles and 4+/4+ in the proximal muscles of both limbs, with normalized CK levels. After three weeks, she was temporarily discharged from our department with a planned operation for ovarian and lung tumors. One month after discharge, total hysterectomy and bilateral adnexectomy were performed at the gynecological department, which revealed ovarian clear cell carcinoma. Approximately two months later, right middle lobectomy was performed, revealing lung metastasis of ovarian clear cell carcinoma. Chemotherapy was initiated for stage IV ovarian clear cell carcinoma when the prednisolone dose was reduced to 7 mg/day, with no recurrence of myositis.

Autoantibodies were examined in detail during the treatment. Other MSAs tested using immunoblotting with the EUROLINE Myositis Antigens Profile 3 (EULOIMMUN, Tokyo, Japan) and immunoprecipitation for anti-KS antibodies were all negative, suggesting that the anti-ARS antibodies detected by the ELISA could be false positives. Furthermore, anti-signal recognition particles and anti-3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR) antibodies, tested by the ELISA (Cosmic, Tokyo, Japan), were both negative. Finally, we confirmed that the positive anti-ARS antibody result obtained by the ELISA was a false positive based on the specific detection methods for anti-ARS antibodies. Consequently, we ultimately diagnosed the patient with paraneoplastic inflammatory myositis.

Discussion

CAM is defined as a condition in which malignancy and IIM, including PM/DM, develop simultaneously. Among patients with CAM, myositis can develop and progress to paraneoplastic myositis, stimulated by the progression of malignancy (4). While any type of malignancy can be associated with the development of myositis, ovarian cancer is the most frequently observed malignancy that leads to paraneoplastic myositis (5). In patients with CAM, myositis can rapidly improve after surgical resection of malignancy. According to a large retrospective cohort study in Hungary, rapid normalization of CK levels was observed in CAM patients who underwent surgical intervention without immunosuppressive therapy (6). In some cases, immunosuppressive therapy is initially administered to patients with myositis. However, the prognosis is poor in patients with CAM without intervention against malignancy (3). In contrast, our patient quickly responded to GC before intervention for malignancy.

The relationship between anti-ARS antibody-positive myositis and malignancy remains controversial compared to anti TIF1-γ antibody-positive myositis and malignancy (2). One study reported no significant association between the development of anti-ARS antibody-positive myositis and the presence or occurrence of malignancy (7). Other reports have demonstrated that 7.4-15.6% of patients are expected to develop malignancy within 3 years before or after the onset of anti-ARS antibody syndrome (8-10). Furthermore, a large cohort study demonstrated that some patients with anti-ARS antibody-positive DM developed malignancy very close to the onset of myositis, and DM patients with both anti-Jo-1 and anti-PL-12 antibodies were observed to have accelerated progression of both DM and malignancy (10). To explain the underlying mechanism of malignancy coexisting with anti-ARS antibody-positive myositis, we propose that the upregulation of certain types of ARS may be involved in the development of malignancy (2,11), which could subsequently trigger the production of anti-ARS antibodies in some patients. Initially, we assumed that this case represented paraneoplastic myositis with anti-ARS antibodies, likely triggered by ovarian cancer. However, we later realized that this was a case of paraneoplastic inflammatory myositis with a false-positive anti-ARS antibody result by an ELISA, as specific measurements using immunoblotting and immunoprecipitation were all negative.

Immunoprecipitation is considered the gold standard for accurate detection of anti-ARS antibodies because of its high sensitivity and specificity (12). However, there is limited evidence on how to manage patients with “false-positive” anti-ARS antibody results, i.e. those who test positive by an ELISA but negative by immunoprecipitation (12). The MESACUP™ anti-ARS test demonstrated 100% sensitivity and 66.7% specificity for identifying patients with anti-ARS antibody syndrome, primarily PM/DM (13). In addition, in the EUROLINE assay, the anti-Jo-1 antibody, the most prevalent anti-ARS antibody in idiopathic inflammatory myopathies, has a reported sensitivity of 21-55% and a specificity of nearly 100% for myositis detection, according to both the manufacturer and the existing literature (14). Therefore, patients may test positive for anti-ARS antibodies by an ELISA while testing negative by immunoblotting, a discrepancy that may be interpreted as a false positive result. Although immunoprecipitation remains the gold standard for detecting anti-ARS antibodies, immunoblotting may provide more accurate detection than ELISA because of the inherent differences in the assay methodology.

Several reports have indicated that some patients with anti-ARS antibodies, who have both active myositis and malignancy, do not exhibit specific histopathological characteristics typically associated with anti-ARS antibody-positive DM (2,15-17). In addition, some cases of malignancy coexisting with anti-ARS antibody-positive myositis have shown predominant CD8⁺ T cells and scarce macrophage infiltration in the muscles, with myositis completely resolved following GC monotherapy (2,15). In our patient, the types of infiltrating cells, including macrophages and CD8+ T cells, were similar to those observed in cases of malignancy coexisting with anti-ARS antibody-positive myositis; however, the relative abundance of these infiltrating cells was significantly different. It has also been reported that anti-Jo-1 antibody-positive DM and anti-HMGCR antibody-positive immune-mediated necrotizing myositis predominantly involve CD68-positive macrophages (18,19), which is similar; however, both of these antibodies were negative in our case. Notably, although we did not observe perifascicular necrosis/atrophy, we found a number of necrotic fibers in the muscle tissues. This was consistent with her weakness and elevated CK levels. We speculated that the immunological condition of promptly producing antibodies and damaging muscles might be related to a favorable response to GC. To better understand the specific pathological findings in patients with ELISA-based anti-ARS antibody-positive paraneoplastic myositis, including the types of infiltrating inflammatory cells, the further accumulation and analysis of cases with specific pathological findings are needed.

In conclusion, we suggest that some patients with paraneoplastic myositis respond well to prompt glucocorticoid treatment, even when anti-ARS antibodies test positive by an ELISA. However, the possibility of false-positive anti-ARS antibody results should be considered, particularly when the clinical features are atypical for anti-ARS antibody-positive PM/DM. In such cases, malignancy-associated immune activation may contribute to myositis through immunological abnormalities, as suggested by the presence of a cytoplasmic ANA pattern and a false-positive anti-ARS antibody result, possibly reflecting reactivity to an unidentified epitope. Furthermore, histopathological findings in the muscle are particularly advantageous for investigating the cause of inflammatory myositis in patients with both anti-ARS antibodies and cancer. To better understand the pathogenesis of paraneoplastic myositis, a detailed analysis of a larger cohort of patients is required.

The authors state that they have no Conflict of Interest (COI).