Eosinophilic myositis/perimyositis: frequency and spectrum of cutaneous manifestations

Rare forms of inflammatory myopathies - part I, generalized forms

INTRODUCTION

The idiopathic inflammatory myopathies traditionally comprise dermatomyositis, polymyositis, immune-mediated necrotizing myopathy, anti-synthetase syndrome, and inclusion body myositis. In this review, we aimed to cover the less common forms of generalized myositis.

AREAS COVERED

We identified rare forms of widespread myositis on the basis of list provided by the homepage of the Neuromuscular disease center of Washington University, USA and on the basis of the authors' knowledge. We searched PubMed® and EMBASE® for relevant articles on these forms with the aim of providing as much as possible information on their clinical manifestations as well as guidance on their work-up and treatment.

EXPERT OPINION

There is substantial heterogeneity among the various rare forms of generalized myositis in terms of their frequency and characterization. Some forms are reasonably well defined, while others may not represent truly well-defined diseases, but rather variants of other myopathies. The landscape of rare forms appears to have evolved over time, with some forms now being better characterized, while others, such as SARS-Cov-2- and immune checkpoint inhibitor-related myositis have come to the fore only in recent years. Knowledge about rare forms of myositis can aid in their recognition and treatment.

Idiopathic eosinophilic myositis: a systematic literature review

Eosinophilic myositis belong to the idiopathic inflammatory myopathies and are defined by an inflammatory infiltrate composed of eosinophils within the muscle. To date, no consensus exists for diagnosis and care of such patients. The aim of this review was to describe clinical and histological presentation, treatment, and outcome of eosinophilic myositis based on a systematic review of all published histologically proven cases of eosinophilic myositis. A total of 453 records were identified in MEDLINE until November 2020. A total of 69 published cases were identified. The analysis of these allowed the distinction of the 3 previously described pathological subtypes: focal eosinophilic myositis (n = 17); diffuse eosinophilic myositis (n = 36); and eosinophilic perimyositis (n = 16). We propose a simple algorithm for diagnosis and treatment strategy for the care of patient with muscular symptoms and blood eosinophilia. This work also highlights eosinophilic myositis pathogenesis and the need for careful investigations in order to rule out differential diagnoses.

Clinical overview of cutaneous features in hypereosinophilic syndrome

The hypereosinophilic syndromes (HES) are a heterogeneous group of disorders defined as persistent and marked blood eosinophilia of unknown origin with systemic organ involvement. HES is a potentially severe multisystem disease associated with considerable morbidity. Skin involvement and cutaneous findings frequently can be seen in those patients. Skin symptoms consist of angioedema; unusual urticarial lesions; and eczematous, therapy-resistant, pruriginous papules and nodules. They may be the only obvious clinical symptoms. Cutaneous features can give an important hint to the diagnosis of this rare and often severe illness. Based on advances in molecular and genetic diagnostic techniques and on increasing experience with characteristic clinical features and prognostic markers, therapy has changed radically. Current therapies include corticosteroids, hydroxyurea, interferon-α, the tyrosine kinase inhibitor imatinib mesylate, and (in progress) the monoclonal anti-interleukin-5 antibodies. This article provides an overview of current concepts of disease classification, different skin findings, and therapy for HES.

Eosinophilia-associated muscle disorders: an immunohistological study with tissue localisation of major basic protein in distinct clinicopathological forms

Aims:

(a) To evaluate tissue eosinophil density, location of eosinophil cytotoxic products, histopathological muscle changes and inflammatory cell types in different eosinophilia-associated myopathies that are clinicopathologically heterogeneous. (b) To determine the immunohistological range of tissue eosinophil density in non-eosinophilic inflammatory myopathies.

Methods:

Muscle biopsy specimens from seven patients with blood and/or tissue eosinophilia and clinicolaboratory myopathic signs (five chronic course myopathies, one subacute onset fasciitis/myositis, one acute myositis), and from 18 non-eosinophilic inflammatory myopathies, underwent routine staining, inflammatory infiltrate immunophenotyping, immunostaining for eosinophil major basic protein (MBP) and transmission electron microscopy examination. Eosinophil and total inflammatory cell counts were statistically analysed.

Results:

Histological examination showed occasional or no infiltrating eosinophils in all cases. MBP staining showed that tissue eosinophil density and percentages in eosinophilia-associated myopathies were significantly higher than in idiopathic myositides. Extracellular MBP diffusion, the hallmark of eosinophil cytotoxicity, was recurrent on sarcolemma and endothelium. Electron microscopy showed eosinophils close to sarcolemma, abundant mast cells, and capillary endothelial swelling. Immunostaining detected a higher mean eosinophil density in idiopathic myositides than previously assessed histologically.

Conclusions:

MBP immunohistology on skeletal muscle, previously performed only for acute eosinophilic polymyositis, suggests that eosinophil-mediated injury of muscle cells may occur in a wider spectrum of less aggressive eosinophilia-associated myopathies than previously thought. As conventional histology is likely to underestimate this leucocyte subset, MBP staining may be a useful tool in the analysis of tissue infiltration of eosinophils as a possible treatment target.

Chronic eosinophilic perimyositis with persistent myalgias

A 43-year-old man with an 8-year history of hypereosinophilia was evaluated for persistent muscle pain. Methotrexate and corticosteroids were ineffective. Examination, limited by pain even with passive motion, showed only mild weakness. Electromyography and muscle enzymes were normal. A needle muscle biopsy specimen revealed eosinophilic perimyositis. This case illustrates that the diagnosis of eosinophilic perimyositis requires histopathological evaluation, which should be pursued in patients with eosinophilia and persistent myalgia despite normal electromyography and muscle enzymes.

Eosinophilia and musculoskeletal disease

Eosinophilia is occasionally a feature of rheumatic disease. The differential diagnosis of eosinophilia includes parasitic infection, systemic vasculitides, eosinophilic arthritis, and myopathies, together with the idiopathic hypereosinophilic syndrome and malignancy. Careful evaluation of the patient should enable an accurate diagnosis to be made. Parasitic infection is the commonest cause of eosinophilia worldwide and can cause systemic disease, as illustrated by the report of Sarcocystis myositis in a group of military personnel in Malaysia. A persistent arthropathy associated with eosinophilia, but not with parasitic infection, has been reported from the far East. Drugs may also cause eosinophilia, and there has recently been much discussion of the relation between Churg-Strauss syndrome and the leukotriene antagonist zafirlukast. The present view is that reduction of steroid dose allows unmasking of previously undiagnosed Churg-Strauss syndrome. The idiopathic hypereosinophilic syndrome may represent a lymphoproliferative process; evidence for this comes from the demonstration that many patients have a clonally expanded population of aberrant T cells.