Antisynthetase Syndrome: Clinical and Diagnostic Profile

Clinical Characteristics

The American College of Rheumatology suggests that antisynthetase syndrome presents with a constellation of six cardinal features: fever, mechanic's hands, Raynaud phenomenon, myositis, interstitial lung disease (ILD), and arthritis 1
The European League Against Rheumatism recommends considering myositis as symmetric proximal muscle weakness developing over weeks to months, causing difficulty rising from chairs, climbing stairs, lifting objects overhead, and combing hair 2
Interstitial Lung Disease is present in a significant proportion of patients and represents a major determinant of morbidity and mortality, according to the American Thoracic Society 1, 2
Arthritis is characterized as inflammatory polyarthritis affecting multiple joints, often seronegative, as stated by the American College of Rheumatology 1, 2

Elevated CPK levels are characteristic of inflammatory myopathies including antisynthetase syndrome, reflecting active muscle inflammation, as noted by the American Association of Neuromuscular and Electrodiagnostic Medicine 2
CPK elevation distinguishes myositis from polymyalgia rheumatica-like syndromes, where CK should be within normal limits, according to the American College of Rheumatology 3, 4
EMG demonstrates characteristic myopathic changes with increased spontaneous activity, as stated by the American Association of Neuromuscular and Electrodiagnostic Medicine 2
EMG should show evidence of myopathy or muscle inflammation, distinguishing true myositis from polymyalgia-like syndromes, as recommended by the American College of Rheumatology 3, 4

Anti-aminoacyl-tRNA synthetase antibodies are the hallmark of antisynthetase syndrome, present in 30-40% of patients with idiopathic inflammatory myopathies, according to the American College of Rheumatology 1
Anti-Jo-1 (anti-histidyl-tRNA synthetase) is the most common antibody, found in approximately 20% of adult patients with idiopathic inflammatory myopathy, as stated by the European League Against Rheumatism 1, 2
A complete myositis-specific antibody panel should be ordered in all patients with suspected inflammatory myopathy, as approximately 80% will have at least one detectable antibody, as recommended by the American College of Rheumatology 2

The American College of Rheumatology suggests that mechanic's hands, characterized by roughened, cracked skin on the fingers, and Raynaud phenomenon, are common features of antisynthetase syndrome, present in a significant portion of patients 5, 6
Fever is a constitutional symptom often present at disease onset, and is a key feature to consider in the diagnosis of antisynthetase syndrome 5, 6
The presence of anti-Jo-1 (anti-histidyl-tRNA synthetase) antibodies is the most common, found in approximately 20% of adult patients with idiopathic inflammatory myopathy, and is often associated with the classic triad of myositis, interstitial lung disease, and arthritis 5, 6
Other antisynthetase antibodies, including anti-PL-7, anti-PL-12, anti-OJ, anti-EJ, and anti-KS, are present in less than 5% of cases, and may be associated with variable clinical manifestations 5, 6

The American Thoracic Society recommends that high-resolution chest CT (HRCT) be performed to assess for interstitial lung disease patterns, which may show characteristic features such as reticular abnormalities, ground-glass opacities, and subpleural and basal predominance 7
Pulmonary function tests typically reveal a restrictive pattern with low diffusing capacity, which is an important feature to consider in the diagnosis of antisynthetase syndrome 8
Muscle biopsy may be necessary to confirm the diagnosis, and typically shows endomysial mononuclear cell infiltrate surrounding and invading nonnecrotic muscle fibers, causing muscle fiber necrosis and regeneration 5, 6

The European Respiratory Society suggests that basic laboratory assessment should include differential blood cell count, and other inflammatory markers such as C-reactive protein and erythrocyte sedimentation rate, to evaluate the extent of inflammation and disease activity 9
Additional autoantibody screening, including antinuclear antibodies, rheumatoid factor, and anti-citrullinated cyclic peptide antibodies, may be necessary to exclude other connective tissue diseases that can mimic antisynthetase syndrome 7, 9

All individuals who test positive for antisynthetase antibodies should undergo an urgent baseline pulmonary assessment because they have a high likelihood of developing rapidly progressive interstitial lung disease. 10
The recommended baseline investigations include high‑resolution chest computed tomography (HRCT), comprehensive pulmonary function testing (spirometry, diffusing capacity for carbon monoxide, and respiratory muscle pressures), and a standard chest radiograph. 10
Patients who carry anti‑MDA5 or any antisynthetase antibody should be referred promptly for baseline HRCT to detect early lung involvement. 10

The interval for pulmonary reassessment is tailored to the patient’s auto‑antibody profile and the presence of prognostic risk factors; those with high‑risk features should have pulmonary function tests and chest radiography performed at least annually. 10
A repeat HRCT scan is indicated whenever new respiratory symptoms emerge or when pulmonary function tests show a decline, to identify disease progression early. 10

Antisynthetase syndrome is considered to carry a low risk of malignancy, in contrast to the markedly higher cancer association seen with dermatomyositis. 11