POS0490 USEFULNESS OF MHC-II IMMUNO-STAINING ON MUSCLE BIOPSIES IN IDIOPATHIC INFLAMMATORY MYOPATHIES

Background

Idiopathic inflammatory myopathies (IIMs) constitute a group of acquired muscular diseases that occur during childhood and adulthood, exhibit a variety of phenotypes and are potentially life-threatening. IIM diagnosis considers clinical, serological, and histological data. Muscle pathological analysis of IIM patients gives relevant elements for the diagnosis (immune cell infiltrate, vascular and connective tissues, as well as myofiber morphology). Immunochemistry (IHC) labeling for major histocompatibility complex class I (MHC-I), and C5b9, that are negative in normal muscle, appeared of interest in IIM diagnosis and the understanding of IIM pathogenesis. In normal muscle, myofibers are negative for MHC-II IHC. Its interest in the neuropathological exam of IIM muscle remains to be better characterized.

Objectives

This study aims to analyze the pattern of MHC-II expression in various IIMs.

Methods

A historical cohort was designed using the MYOLYON register (IIM patients diagnosed between 2016 and 2020 at the University Hospital of Lyon, France). Inclusion criteria were IIM diagnosis that was established histologically and available frozen muscle samples for additional analyses. Exclusion criterium was any treatment before muscle biopsy. Demographical data and final diagnosis were collected retrospectively from medical records. A centralized, standardized, and blind analysis of muscle MHC-II immuno-staining was conducted to define the various patterns of MHC-II by myofibers and by capillaries. The study complied with ethical requirements.

Results

Seventy-three patients were included: 23 dermatomyositis (DM), 13 anti-synthetase syndrome (ASS), 13 immune-mediated necrotizing myopathies (IMNM), 13 inclusion body myositis (IBM), and 11 overlap myositis (OM). MHC-II immuno-staining of myofibers or capillaries was abnormal for 91.8% of the analyzed biopsies (Figure 1). The analysis of MHC-II myofiber immuno-staining revealed distinguishable patterns according to IIM subtype: the labeling was diffuse in IBM (69.2%, n=9/13), perifascicular in ASS (61.5%, n=8/13), and variable in OM (patchy for 27.3% n=3/11 or clustered for 36.4%, n=4/11). MHC-II immuno-staining was negative in IMNM (84.6%, n=11/13) and in DM (47.8%, n=11/23). DM exhibiting positive MHC-II myofibers (n=12) were associated with the presence of anti-TIF1γ, anti-NXP2 and anti-SAE auto antibodies (n=5, n=3 and n=2, respectively). Among the 12 patients, there were juvenile cases (n=5, 41.7%) or DM associated with ongoing neoplasia (n=4, 33.3%). Three main architectures were described for capillaries: giant, leaky and capillary dropout. Patterns of MHC-II positive capillaries were the following: DM was characterized by capillary dropout (68.2%), IMNM showed leaky capillaries (75.0%), IBM giant capillaries (66.7%), ASS exhibited both giant (61.5%) and/or leaky (58.3%) capillaries, while OM showed giant (63.6%) or/and leaky (80.0%) capillaries and capillaries dropout (60.0%).

Conclusion

The present work establishes the usefulness of MHC-II immuno-staining for IIM diagnosis, and gives additional elements on the impairment of myofibers and capillaries in the various IIM subgroups. MHC-II expression is known to be induced by inflammatory cytokine such as interferon type II. This could be linked to myofiber and/or capillary impairment in some IIMs, such as IBM, ASS and OM. These results also support the implication of vasculopathy in IIM pathogenesis, with various structural and cellular consequences regarding the different subgroups. Finally, MHC-II immuno-staining in IIM muscle biopsies enables a foremost analysis of myofibers and capillaries, and represents an additional biomarker to distinguish IIM subgroups.

References

[1]De Bleecker, J.L. et al. 205th ENMC International Workshop: Pathology diagnosis of idiopathic inflammatory myopathies part II 28-30 March 2014, Naarden, The Netherlands. Neuromuscul Disord 2015, 25, 268-272.

Disclosure of Interests

None declared.

POS0862 INAUGURAL DROPPED HEAD SYNDROME AND CAMPTOCORMIA IN INFLAMMATORY MYOPATHIES

Background

The idiopathic inflammatory myopathies (IIMs) are a heterogeneous group of diseases that can affect the muscles, skin, lungs, heart, and joints. Increase knowledge about histopathological findings, clinical manifestations and auto-antibodies have allowed further novel classification of IIMs. Today, the main IMs subgroups are: dermatomyositis (DM), inclusion body myositis (IBM), immune-mediated necrotizing myopathies (IMNM), overlap myositis (OM) and immune-checkpoint inhibitor-related myositis (ICIrm). Axial muscle involvement results either in a “Dropped Head Syndrome (DHS)”, with a marked weakness of the neck extensors, or in a camptocormia (CC), with a weakness of the thoracolumbar paraspinal muscles. This atypical presentation is poorly described in the course of IMs while it may results in a major disability, and may lead to myositis diagnosis delay.

Objectives

This study aimed to describe IMs revealed by DHS and/or CC. Secondary outcomes were to define subgroups of patients according to clinical, biological and histopathological characteristics. Then, the effects of treatments used were analyzed.

Methods

A historical cohort was designed using the register MYOLYON which includes all IMs followed at the University Hospital of Lyon (France) between 2000 and 2021. All patients with IM revealed by DHS and/or CC and having an histologically proven IMs were included, after exclusion of alternative (e.g., myasthenia gravis, motoneuron disease). Clinical, biological, immunological, histopathological data as well as outcome and care were collected through a standardized form. Agreement for the study was obtained from the French Ministry of the Research and the study was approved by the Local Research Ethics Committee.

Results

Twenty-two patients were fully characterized: DM (n=4), IBM (n=7), OM (n=8), ICIrm (n=2) and one myositis with anti-Hu antibodies. Two groups of patients were identified according to the age at first symptoms and to the type of muscle axial involvement (e.g, DHS and/or CC). Before the age of 70 (n=13/22), the two most common diagnoses (n=11/13) were DM (n=4/4) and OM (n=7/8). Axial muscle involvement was diffuse (DHS and CC) in 10/13 patients. After 70 years old (n=9/22), there were a majority of IBM (n=6/9) and all cases of ICIrm (n=2). Axial involvement was restricted to one group of muscles (DHS or CC) in 5/9 patients. Finally, 77% (17/22) of patients had refractory disease and required a second line treatment (e.g, immunoglobulins). All of these results are summarized in the Figure 1.

Figure 1.

Conclusion

While IM diagnosis is challenging in the presence of inaugural axial involvement, these results highlight the subset of IM to be considered according to the age at first symptoms and the type of axial involvement (e.g., DHS and/or CC).

References

[1]Mariampillai, K. et al. Development of a New Classification System for Idiopathic Inflammatory Myopathies Based on Clinical Manifestations and Myositis-Specific Autoantibodies. JAMA Neurol75, 1528-1537 (2018).

[2]Landon-Cardinal, O. et al. Recognising the spectrum of scleromyositis: HEp-2 ANA patterns allow identification of a novel clinical subset with anti-SMN autoantibodies. RMD Open6 (2020).

[3]Suarez, G.A. & Kelly, J.J., Jr. The dropped head syndrome. Neurology42, 1625-1627 (1992).

[4]Oerlemans, W.G. & de Visser, M. Dropped head syndrome and bent spine syndrome: two separate clinical entities or different manifestations of axial myopathy? J Neurol Neurosurg Psychiatry65, 258-259 (1998).

Disclosure of Interests

None declared