4. A case of SAE-1 dermatomyositis

INTRODUCTION: Dermatomyositis is a rare, acquired inflammatory myopathy. The panel of myositis specific antibodies (MSAs) continues to grow and inclusivity of MSAs in myositis autoantibody testing can vary among trusts. Our patient had serology and clinical features in keeping inflammatory myopathy associated with one of the more recently found MSAs- SAE-1. CASE DESCRIPTION: A 63-year-old man developed a purple rash over his scalp in July 2018. He was previously fit and well apart from childhood rheumatic fever. He was a non-smoker. The rash spread over his face, forearms and feet. He developed discomfort and weakness in his neck, upper arms and thighs in September 2018 with increasing difficulty walking up stairs and lifting boxes and driving. In October 2018 he developed progressive dysphagia and was struggling to swallow semi-solid food and then liquids too. A skin biopsy showed mild papillary dermal inflammatory infiltrate in keeping with possible dermatomyositis or systemic lupus. The patient was admitted to hospital in December 2018 with progression of the rash, proximal weakness and swallowing difficulty and referred to rheumatology. He lost over 7kgs in weight between October and December 2018. He denied any fever or symptoms suggestive of a connective tissue disease. On examination he had a purple rash on his scalp, over the malar distribution and upper back. He had a heliotrope rash over his eyelids and gottrens papules. He had 4/5 weakness in hip and shoulder flexors. He also had bibasal crepitations from his lungs on auscultation. Investigations revealed a serial normal creatine kinase (CK) and transaminases. A myositis panel revealed the SAE-1 autoantibody. CT thorax, abdomen and pelvis revealed some inflammatory changes at the bases of both lungs in keeping with organising pneumonia. Upper and lower GI endoscopy was unremarkable. An MRI revealed inflammation of multiple muscles including gluteus maximus and minimus, iliopsoas, paraspinal muscles and posterior abdominal wall in keeping with polymyositis. He was commenced on prednsiolone 40mg for 3 months after a pulse intravenous methylprednisolone. He noticed great improvement with proximal myopathy, dysphagia and rash within a week of commencing treatment. He was started on azathioprine at 2mg/kg in December 2018. DISCUSSION: The SAE-1 autoantibody targets the auto-antigen SUMO-1 facilitating protein sumoylation. Previous cohort studies have shown skin manifestations and dysphagia as predominant clinical characteristics in SAE-1 dermatomyositis. Our patient had features of interstitial lung disease which has previously been reported as rare in such patients. Our patient also had a normal serial CK and transaminases despite having proximal clinical weakness and on activity on radiological modality. Our patient had SAE-1 positive dermatomyositis which has responded quickly to corticosteroids. Azathioprine was chosen ahead of other immunosuppressive therapy after discussion with the dermatology team as cutaneous manifestations were predominant. The patient remains in remission on azathioprine. KEY LEARNING POINTS: SAE-1 dermatomyositis is very steroid responsive and remission can be maintained on azathioprine when there are widespread cutaneous manifestations, dysphagia and mild ILD. The case serves as an important reminder that CK levels can be normal in active myositis. A normal CK should not stop further investigations where clinical suspicion for inflammatory myopathy remains high. SAE-1 positive dermatomyositis is a heterogeneous inflammatory myopathy. Our patient had skin manifestations and dysphagia as reported in many previous case reports however they also had features in keeping with organising pneumonia which has been reported as a rarer finding in SAE-1 dermatomyositis. A multi-disciplinary approach to such patients is paramount. This case involved team work between rheumatology, dermatology, respiratory medicine and radiology. CONFLICTS OF INTEREST: The authors have declared no conflicts of interest.