Clinical utility of anti-cytosolic 5'-nucleotidase 1A antibody in idiopathic inflammatory myopathies.

Chiseko Ikenaga,Joshua C Kershen,Conrad C Weihl,Leo H Wang,Tahseen Mozaffar,Andrew R Findlay,Yessar Hussain,Robert C Bucelli,Michael Wallendorf,Brent A Beson,Jonathan Cauchi,Namita A Goyal,Alan Pestronk,Sarah Robinson

doi:10.1002/acn3.51294

Abstract

ObjectiveTo define the clinicopathologic features and diagnostic utility associated with anti‐cytosolic 5′‐nucleotidase 1A (NT5C1A) antibody seropositivity in idiopathic inflammatory myopathies (IIMs).MethodsAnti‐NT5C1A antibody status was clinically tested between 2014 and 2019 in the Washington University neuromuscular clinical laboratory. Using clinicopathologic information available for 593 patients, we classified them as inclusion body myositis (IBM), dermatomyositis, antisynthetase syndrome, immune‐mediated necrotizing myopathy (IMNM), nonspecific myositis, or noninflammatory muscle diseases.ResultsOf 593 patients, anti‐NT5C1A antibody was found in 159/249 (64%) IBM, 11/53 (21%) dermatomyositis, 7/27 (26%) antisynthetase syndrome, 9/76 (12%) IMNM, 20/84 (24%) nonspecific myositis, and 6/104 (6%) noninflammatory muscle diseases patients. Among patients with IBM, anti‐NT5C1A antibody seropositive patients had more cytochrome oxidase‐negative fibers compared with anti‐NT5C1A antibody seronegative patients. Among 14 IBM patients initially negative for anti‐NT5C1A antibody, three patients (21%) converted to positive. Anti‐NT5C1A antibody seropositivity did not correlate with malignancy, interstitial lung disease, response to treatments in dermatomyositis, antisynthetase syndrome, and IMNM, or survival in IIMs.InterpretationAnti‐NT5C1A antibody is associated with IBM. However, the seropositivity can also be seen in non‐IBM IIMs and it does not correlate with any prognostic factors or survival.

Highlights

Inclusion body myositis (IBM) is an idiopathic inflammatory myopathy (IIM) that typically affects patients over the age of 50.1 Patients with IBM are clinically characterized by asymmetric finger flexion and knee extension weakness.[1]
AntiNT5C1A antibody seropositive patients had a lower serum CK (P < 0.01), higher frequency of antinuclear antibody seropositivity (59% vs. 18%; P < 0.01), higher frequency of dysphagia (45% vs. 28%; P < 0.01), and the presence of major histocompatibility complex (MHC)-class[1] expression (87% vs. 70%; P < 0.01), compared with seronegative patients. To see if these differences were due to the overrepresentation of IBM patients in the anti-NT5C1A antibody seropositive group, we performed a similar analysis that removed the 249 patients with IBM and looked at 240 non-IBM IIMs (Table 2)
Similar to the previous group, antiNT5C1A antibody seropositive non-IBM IIM patients had a lower serum CK (P = 0.02) and a higher frequency of antinuclear antibody (45% vs. 18%; P < 0.01)

Summary

Introduction

Inclusion body myositis (IBM) is an idiopathic inflammatory myopathy (IIM) that typically affects patients over the age of 50.1 Patients with IBM are clinically characterized by asymmetric finger flexion and knee extension weakness.[1]. NT5C1A antibody can be detected in autoimmune diseases other than IBM, seropositivity for antiNT5C1A antibody in IIMs other than IBM has not been assessed within a large population. The relationship between seropositivity for anti-NT5C1A antibody and other clinicopathologic features in IBM or dermatomyositis have been discussed and some report that seropositivity for anti-NT5C1A antibody in IBM or juvenile myositis predict a more severe phenotype.4,10À12 This relationship has not been assessed in other IIMs. Diagnostic testing for myositis specific and myositis associated antibodies is routinely performed in patients a 2021 The Authors.

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