P024 Dermatomyositis, a blurred clinical picture
Authors: Maltas Lucy , Vila Josephine , Ray Anish 
Published: April 2024

Abstract

Background/Aims
We present a case of MDA5 dermatomyositis(DM) in a 25-year-old male, initially presenting with seronegative inflammatory polyarthritis affecting the hands. No classic features of DM were noted and CK was normal. Sulfasalazine was started and subsequently stopped after an ALT rise. Lung-function performed prior to planned methotrexate was abnormal. A CT neck, thorax and abdomen showed unusual pulmonary appearances with focal basal ground glass opacities with reverse halo, without widespread interstitial lung disease(ILD). A bronchoscopy excluded atypical infection. He then developed scaly lesions over the extensor PIPJs, periungual lesions, periorbital swelling and sicca symptoms. CK remained normal, extended myositis screening was negative. LDH and troponins were elevated. A skin biopsy of the hand rash was consistent with dermatomyositis.

Methods
Muscle pain persisted and an MRI proximal muscles showed muscle oedema and inflammation. A muscle biopsy was requested but not performed as he developed an olecranon bursa with staphylococcal aureus infection. The bursa broke down, required wash-outs, antibiotics and was left to heal by secondary intention. A repeat myositis screen was positive for MDA5 antibody. Immunosuppression was delayed because of concerns that prednisolone, Mycophenolate mofetil(MMF) or Rituximab would cause further wound breakdown and increased risk of infection. The patient was monitored with serial lung-function but didn’t develop ILD. Dermatology confirmed there was active dermatomyositis in the wound edges. The wound only finally healed with additional IVIG therapy. The patient is now established on Rituximab, having been unable to tolerate MMF.

Results
This case highlights that continued reassessment of the evolving clinical picture is vital to reach the correct diagnosis, and that one should not be reassured by a normal CK. Instead the ALT rise (along with mild elevations of LDH and troponin) was likely reflecting muscle inflammation, not liver inflammation secondary to Sulfasalazine. The repeatedly infected olecranon bursa and large open wound raised concerns about immunosuppressive agents. However, the lack of healing was due to active DM and escalation of treatment was required rather than treatment delay. IVIG was given with excellent and rapid effect. This is licensed for refractory skin involvement in DM, to be considered when infection concern is high.

Conclusion
The pulmonary involvement with reverse halo sign was felt by the MDT to be nonspecific initially, with a wide differential. In the clinical context, this was reflecting an atypical presentation of MDA5 positive ILD. This antibody can be associated with rapidly progressive ILD and death in approximately one third of cases. Had our patient shown evidence of significant pulmonary progression, high dose immunosuppression would have been commenced despite potential infection risk. Not all patients testing positive for MDA5 develop rapidly progressive ILD but clinical suspicion should be high with frequent serial monitoring of lung function and radiology.

Disclosure
L. Maltas: None. J. Vila: None. A. Ray: None.