Case Presentation: A 57-year-old man presented with a one-year history of weakness in his proximal muscles that had progressively worsened. He was wheelchair bound at presentation. He endorsed arthalgias, subjective fevers, and night sweats. He denied any dyspnea, rashes, dysphagia, or statin use. Temperature was 98.5F, heart rate 68 bpm, blood pressure 98/67 mmHg, respiratory rate 18 breaths/min, oxygen saturation 97% on RA. Grip strength was reduced and patient unable to make full fist. Active synovitis and swelling was noted to all metacarpophalangeal joints and wrists. The knees were slightly warm to palpation with small effusions. Tenderness was noted at essentially all areas palpated on musculoskeletal exam. Strength was reduced to 4/5 in the upper and lower extremities with the proximal muscle groups being weaker. No rashes were noted.Laboratory data returned with elevation of WBC (15.6 K/microliter), CK (3441 U/L), ESR (97 mm/hr), and CRP (11.3 mg/dL). RF, ANA, and ANCA were negative. ENA antibody panel was negative, except for Anti-Jo1 positive at 8.0 (reference range <1.0 neg) and anti-centromere B positive at 2.6 (reference range <1.0 neg). Aldolase was 27.5 U/L. Myositis panel confirmed Anti-Jo-1 Ab positive. Muscle biopsy of left upper thigh was consistent with inflammatory myopathy.CT chest with contrast revealed bibasilar subpleural reticular and ground glass opacities with associated mild traction bronchiectasis displaying an early non-specific interstitial pneumonia pattern. MRI of the lower extremity returned with diffuse left lower extremity myositis along with a left knee effusion with evidence of synovitis. Periarticular demineralization marginal erosions was noted on hand x-ray, concerning for autoimmune arthritis.The patient was diagnosed with anti-synthetase syndrome and improved with oral corticosteroid treatments. Hydroxychloroquine and methotrexate were also initiated for treatment of his myositis and suspected seronegative RA.

Discussion: Idiopathic inflammatory myopathies (IIM) comprise a group of rare autoimmune diseases. Most clinicians are familiar with dermatomyositis and polymyositis, but anti-synthetase syndrome is less widely known. Anti-synthetase syndrome is characterized by ILD, myositis, and the presence of anti-aminoacyl-tRNA synthetase (anti-ARS) antibodies. Mechanic’s hands, Raynaud’s phenomenon, and arthritis all can help support the diagnosis of anti-synthetase syndrome. Eight different anti-ARS antibodies exist with the most common being anti-Jo-1, which is found in 20-30% of patients with polymyositis. Muscle biopsy can be used to diagnose IIM, but cannot be used to distinguish DM, PM, or anti-synthetase syndrome as the common histological feature seen in skeletal muscle is not specific. Inflammatory infiltrates are often missed on muscle biopsy due to their patchy pattern. HRCT is used to diagnose ILD and the most common pattern is NSIP with traction bronchiectasis and ground glass opacities. Anti-ARS antibodies can be tested through a myositis panel. Antibody levels fluctuate based on disease activity, so absence of antibodies does not preclude the presence of disease.Treatment of anti-synthetase syndrome generally begins with steroids. Steroids are the main therapy, but DMARDs such as azathioprine and methotrexate are frequently added as first-line adjunct to steroids.

Conclusions: IIM compromise a rare group of autoimmune diseases. Recognition of the clinical features can lead to appropriate work-up, diagnosis and treatment.