P047 An unusual case of dermatomyositis with co-existent anti-GAD and anti-NXP2 antibody positivity

Abstract

Abstract Background/Aims Dermatomyositis (DM) is a rare disease. We present a case of DM with both anti-nuclear matrix protein 2 antibody (NXP2) as well as anti-glutamic acid decarboxylase antibody (GAD) positivity, the combination of which has yet not been documented in the current literature. Methods The case is described below. Results A 48 year old Caucasian male with no co-morbidities presented with a one-month history of sore throat and lethargy, followed 2 weeks later by muscular pain in his upper arms. On examination, there was erythema to the sun-exposed areas of the face and arms, hoarse voice and Gottron’s papules. He had proximal muscle weakness of 4/5 in his shoulder and hips. His creatinine kinase(CK) was elevated at 2914U/L. He was started on methylprednisolone 1 gram od for 3 days with improvement of his CK to 642U/L. His muscle biopsy showed mild chronic neurogenic changes and upregulation of C5b-9 but no evidence of inflammatory myopathy which was attributed to the steroid use prior to the biopsy. His myositis antibody screen was positive for Anti-Nuclear Matrix Protein antibody 2(NXP2). After 4 days he developed rapid onset dysphagia and a sudden drop in his spirometry readings with a fall in his FEV1from 94% to 85% and a fall in his FVC from 88% to 79%. He became acutely unwell, drowsy with difficulty completing sentences and global weakness. His CK had risen to 1567U/L despite the high dose intravenous methylprednisolone. He was diagnosed with Diabetic ketoacidosis(DKA) with a blood glucose of 32mmol/L , pH of 7.0, and transferred to ITU. Intravenous immunoglobulin (IVIG) was administered with subsequent improvement in all muscle groups. He was then commenced on a subcutaneous insulin regime and pulsed intravenous cyclophosphamide (Eurolupus) as his EMG showed a sensorimotor polyneuropathy as well as an inflammatory myopathy. His serology was negative for infectious aetiology. Malignancy screen including PET scan, oesophagogastroduodenoscopy and colonoscopy were normal however, he was found to be positive for anti-GAD antibody. Conclusion GAD antibodies are known to be associated with many disorders including diabetes and stiff person syndrome and can recognise different epitopes in various diseases. This is the first documented case of GAD occurring in a DM patient, in the presence of NXP2 antibodies. IVIG is used to treat both stiff man syndrome and refractory DM. It is possible that the combination of GAD and NXP2 contributed to the pathogenesis and severity of the clinical presentation in this case. Disclosure K. Beharry: None. G. Barminski: None. D. De Lord: None.