7. Anti-MDA5 associated dermatomyositis
Authors: Laverty Ursula , Benson Claire 
Published: September 2019

Abstract

Introduction
This is a complex case of a 50-year-old lady who presented with peripheral synovitis, fever and rash. She developed ulcerative skin lesions, proximal muscle weakness and pulmonary fibrosis.

Case description
A 50-year-old woman presented with a 6-week history of joint pain and swelling, an erythematous rash and fever. No preceding illness. She had fibromyalgia and chronic low back pain. She had several courses of prednisolone 20mg for presumed reactive arthritis with no benefit. She was a non-smoker, did not drink alcohol and was unemployed. She had florid symmetrical synovitis affecting MCPs, PIPs, wrists, ankles and knees. She had an erythematous rash across her face, chest and upper arms. She was pyrexic at night when her skin became inflamed.
ESR-35 and CRP-13. RF, anti-CCP, ANA, ANCA, ACE and ASOT titre were negative. U&E was normal. LFTs were elevated with GGT-113, ALP-143, AST-432 and ALT-281. CK-33, LDH-367 and ferritin-2573. CXR, urine dip and liver screen were normal. USS abdomen, ECHO, CT CAP and PFTs were normal. Skin biopsy showed features of interface dermatitis. Extended myositis panel was negative. MRI of thighs showed active myositis. Muscle biopsy was insufficient. Tumour markers, mammogram, USS of breasts, OGD and colonoscopy were normal. The working diagnosis was dermatomyositis.
She was treated with hydroxychloroquine and prednisolone 60mg with little benefit. She had three pulses of IV methylprednisolone with good benefit for joints. Azathioprine was not tolerated. Skin worsened and she was treated with 5 days IV immunoglobulins. She developed ulcerating skin lesions and swabs confirmed pseudomonas which was treated with ciprofloxacin and topical steroids. Dapsone caused haemolysis. She was switched to mycophenolate. Joints flared when prednisolone was reduced below 60mg and she was treated with rituximab. She developed proximal muscle weakness. Repeat MRI of thighs showed further progression of active myositis. Extended myositis panel confirmed Anti-MDA5 myositis. HRCT showed established pulmonary fibrosis. The myositis tertiary referral centre recommended IV cyclophosphamide. She responded well with improvement in joints and skin and prednisolone was weaned.

Discussion
This was a refractory case of anti-MDA 5 myositis which failed to respond to multiple immunosuppressive treatments. The patient failed high dose oral steroids initially and therefore treatment was escalated to IV methylprednisolone. Her joint disease responded but unfortunately her skin deteriorated. We treated with IV immunoglobulins with no benefit. She was unable to tolerate azathioprine and was switched to mycophenolate as an alternative steroid sparing agent. Despite steroids, mycophenolate and immunoglobulins her disease progressed with worsening myositis, ulcerating skin lesions and pulmonary fibrosis. Rituximab is a well-recognised potential treatment option for patients with myositis resistant to conventional treatment. The extended myositis panel revealed anti-MDA5 myositis, which is associated with rapidly progressive interstitial lung disease and ulcerative skin lesions. These are case reports in Rheumatology in 2017 which describe successful treatment with rituximab for anti-MDA5 myositis. However in this particular case, our patient failed to respond to rituximab. Cyclophosphamide is reserved for severe cases of myositis with rapidly progressive lung disease. We took the opportunity to discuss this case with the tertiary myositis referral centre in Liverpool and they advised to proceed with cyclophosphamide with good benefit.
This was an interesting case of anti MDA 5 myositis. The initial presentation was not classical for an inflammatory myopathy with peripheral synovitis, fever and a rash. This patient’s signs and symptom evolved with development of muscle weakness and pulmonary fibrosis. CK was normal and this highlights the importance of checking other muscle enzymes in cases of suspected myositis. An extended myositis panel is also invaluable and helped to confirm the diagnosis in this particular case.

Key learning points
It is important to consider anti-MDA5 dermatomyositis particularly if patient presents with polyarthritis and ulcerative skin lesions. CK may be normal in myositis and it is important to check other muscle enzymes. There are five muscle enzymes to consider in cases of suspected myositis including CK, aldolase, AST, ALT and LDH. It is important to consider myositis if a patient presents with raised ALT and AST without underlying liver disease. If the Royal Free myositis panel is negative, consider sending research myositis panel to Bath.

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