Granulomatous Myositis Showing Fluctuating "Leopard-Man" Sign: A Case Report on FDG PET/CT Imaging

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.

A "Leopard Man" Aspect on 18 F-FDG PET/CT Revealing a VEXAS Syndrome

ABSTRACT

VEXAS (vacuoles, E1 enzyme, X-linked, autoinflammatory, somatic) syndrome is an adult-onset autoinflammatory disease caused by somatic UBA1 mutations first described in 2020. Most of these patients met clinical criteria for an inflammatory syndrome (relapsing polychondritis, Sweet syndrome, polyarteritis nodosa, or giant-cell arteritis) or a hematologic condition (myelodysplastic syndrome or multiple myeloma) or both. We described here an FDG PET/CT "leopard man" appearance, with abnormal marrow recruitment the findings, in a 70-year-old man diagnosed with a VEXAS syndrome.

FDG/PET-CT findings in a first series of 10 patients with polyarteritis nodosa

OBJECTIVE

18F-fluorodeoxyglucose positron emission tomography with computed tomography (FDG-PET/CT) is widely used in patients with large-vessel vasculitis. The benefits of FDG-PET/CT in polyarteritis nodosa (PAN) has only ever been assessed in three case reports. Our aim was to describe FDG-PET/CT findings in 10 patients with newly diagnosed PAN.

METHODS

This was a retrospective study of patients with PAN who underwent FDG-PET/CT at diagnosis, between 2017 and 2020. The FDG-PET/CT data were analysed retrospectively.

RESULTS

Ten patients were included: nine men and one woman with a median age of 67 (43-78) years. PAN was diagnosed according to ACR criteria in nine patients, and histologically in one case. All patients had high C-reactive protein levels (median, 223 mg/l). The main FDG-PET/CT abnormality was increased tracer uptake in the muscles, particularly in the connective tissue (perimysium, epimysium) (n = 7), in linear (n = 5) or focal (n = 2) patterns. Increased FDG uptake in large-diameter vessels was observed in four patients, in the humeral (n = 4), femoral (n = 1) and the common interosseous arteries (n = 1). Nine patients had bone-marrow FDG uptake, six had splenic FDG uptake. Three had synovitis and three had lymph-node uptake. One patient had subcutaneous FDG uptake, with a "leopard skin" appearance.

CONCLUSIONS

FDG-PET/CT seems to be a useful non-invasive imaging technique for diagnosing PAN, particularly in patients with non-specific systemic features. Tracer uptake in muscular connective tissue seems to be a recurrent sign in patients with PAN and may be pathognomonic.