11. An unusual case of dermatomyositis with anti-small ubiquitin-like modifier activating enzyme (SAE) antibodies present
Authors: Brown Geraint , Ludwig Dalia , Lazarus Mark 
Published: September 2019

Abstract

Introduction
Idiopathic inflammatory myopathies (IIM) have long been diagnosed using a defined number of clinical criteria (Bohan and Peter). The emergence of new myositis specific antibodies (MSAs) and their 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 of the disease, and severe dysphagia were prominent clinical features in addition with the presence of anti-small ubiquitin-like modifier activating enzyme (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 throughout the lungs.
An endoscopy revealed severe gastritis. Oropharyngeal examination revealed pooling of saliva and mucositis. Ceftriaxone was commenced for a presumed infective aetiology.
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, with marked proximal upper and lower limb weakness.
Nerve conduction studies revealed normal sensation, and most motor nerves had normal conduction velocities with small nerve responses. Electromyography showed areas with denervation.
With no improvement in the patient’s condition, anti-tuberculosis and anti-fungal therapy were commenced, with pulsed methylprednisolone for three days followed by 80mg daily to cover for an organizing pneumonia. Subsequent cultures were negative.
Progressive weight loss with muscle wasting ensued and later, facial hyperpigmentation was noted in addition to the development of facial, lip and arms swelling. He was 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 uptake in the muscles posterior of the neck, tongue and masticators.
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 the presence of anti-SAE antibodies confirmed the diagnosis.
Pulsed methylprednisolone, immunoglobulin therapy, and azathioprine were initiated with reducing prednisolone dose.

Discussion
This case of DM with a generalised rash, severe dysphagia and limb subcutaneous oedema were salient features in addition to the presence of anti-SAE antibodies. Anti-SAE has been shown to be present exclusively in DM patients where rash and severe dysphagia are common clinical findings. Our patient presented with severe dysphagia, which can 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-CT in our case confirmed the involvement of the muscles of mastication thus could prove a useful tool when investigating involvement of swallowing muscles in patients with anti-SAE DM.
Skin features are another common finding in the anti-SAE group and our patient had a heliotrophic rash and shawl sign, which responded poorly to 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, in addition with azathioprine and methotrexate.
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.
The presence of limb and facial oedema may be an overlying feature of the anti-SAE group; however, previous cases of limb oedema have not identified this antibody as the SAE test was unavailable. The presence of severe dysphagia and subcutaneous oedema suggests the presence of anti-SAE lends itself to a clinical phenotype of DM that is particularly severe and requires multidisciplinary input.

Conflicts of interest
The authors have declared no conflicts of interest.