11. An unusual case of dermatomyositis with anti-small ubiquitin-like modifier activating enzyme (SAE) antibodies present

Abstract

Introduction: Idiopathic inflammatory myopathies (IIM) have long been diagnosed using a defined number of clinical criteria (Bohan and Peter). Theemergenceofnewmyositis specificantibodies(MSAs)andtheir relation to specific disease phenotypes may be useful in establishing a new clinical-serological diagnostic criteria for different disease presentations and thus help to determine management and prognosis. We present a case of dermatomyositis (DM) where limb subcutaneous oedema; a rare manifestation ofthe disease,andseveredysphagiawereprominent clinicalfeaturesinadditionwiththepresenceofanti-smallubiquitin-likemodifieractivatingenzyme( SAE)antibodies. Case description: A 63-year-old Pakistani male presented with weight loss, anorexia, odynophagia, and a rash over his scalp, chest, face and flexor surfaces. Initial blood results revealed hypoalbuminaemia, CRP 7mg/L and ESR 37mm/h. A CT chest revealed an anterior mediastinum soft tissue mass suggestive of necrosis, with multiple ill-defined nodes throughoutthelungs. An endoscopy revealed severe gastritis. Oropharyngeal examination revealed pooling of saliva and mucositis. Ceftriaxone was commenced forapresumedinfectiveaetiology. Video fluoroscopy confirmed pharyngeal dysphagia with aspiration. Examination demonstrated a non-fatigable bulbar sounding dysarthria. There was no tongue wasting or fasciculations. Power was globally reduced,withmarkedproximalupperandlowerlimbweakness. Nerve conduction studies revealed normal sensation, and most motor nerves had normal conduction velocities with small nerve responses. Electromyographyshowedareaswithdenervation. With no improvement in the patient's condition, anti-tuberculosis and anti-fungal therapy were commenced, with pulsed methylprednisolone for three days followed by80mgdaily to cover for an organizing pneumonia. Subsequentcultureswerenegative. Progressive weight loss with muscle wasting ensued and later, facial hyperpigmentationwas noted in addition to thedevelopment of facial, lip and arms swelling. Hewas rheumatoid factor positive>500 iu/ml, with a raised IgE 2912 g/L and IgG 37.6 g/L. A CT-PET scan revealed intense uptakeinthemusclesposterior oftheneck,tongueandmasticators. An MRI scan of his arms revealed several abnormal signals around the shoulder girdle, long muscles of the back, and upper arm, which guided the site for muscle biopsy. This revealed highly abnormal skeletal muscle with frequent atrophic and necrotic fibres overrun by macrophages and T-cell rich inflammation. These findings in addition to serology reporting thepresenceofanti-SAEantibodiesconfirmedthediagnosis. Pulsed methylprednisolone, immunoglobulin therapy, and azathioprine wereinitiatedwithreducingprednisolonedose. Discussion(s): This case ofDMwith a generalised rash, severe dysphagia and limb subcutaneous oedema were salient features in addition to the presenceofanti-SAEantibodies.Anti-SAEhasbeenshowntobepresent exclusively inDMpatientswhererashandseveredysphagiaarecommon clinical findings.Ourpatient presented with severedysphagia,whichcan be difficult to manage requiring enteral feeding. Video fluoroscopy was particularly useful in this case helping to stratify the severity of dysphagia and we would urge other clinicians to use this tool when investigating patients with suspected dermatomyositis to avoid potential complications of poor swallow including aspiration pneumonia. The additional imaging modality of PET-CTin our case confirmed the involvement of the muscles of mastication thus could prove a useful tool when investigating involvementofswallowingmusclesinpatientswithanti-SAEDM. Skin features are another common finding in the anti-SAE group and our patienthadaheliotrophicrashandshawlsign,whichrespondedpoorlyto treatment. We describe the additional feature of severe subcutaneous limb and facial oedema, a rare manifestation of the disease, described in only a few other cases. Limb subcutaneous oedema is thought to reflect underlying severe muscle disease, is difficult to treat, and often is unresponsive to conventional treatment. Our case, and several other cases with the presence of limb oedema as reported in a literature search, required treatment with intravenous immunoglobulin and glucocorticoids, inadditionwithazathioprineandmethotrexate. This is the first reported case to our knowledge of a patient with positive ANA, RF, anti-ccp, and anti-small ubiquitin-like modifier activating enzyme(anti-SAE)antibodies. Key learning points: The finding of anti-SAE in our case where severe dysphagia was present provides further weight to this antibody being a useful serological marker to identify this subgroup of DM patients. Identifying this antibody may be helpful in creating management strategies for these patients and determining disease progression and prognosis. Thepresenceoflimbandfacialoedemamaybeanoverlying feature ofthe anti-SAEgroup;however,previouscasesoflimboedemahavenotidentified thisantibodyastheSAEtestwasunavailable.Thepresenceofsevere dysphagia and subcutaneous oedema suggests the presence of anti-SAE lends itself to a clinical phenotype of DM that is particularly severe andrequiresmultidisciplinary input. Conflicts of interest: The authors have declared no conflicts of interest.