Table 1:

Clinical characteristics of the main clinical and phenotype-specific autoantibody groups in inflammatory myopathies

	Clinical features	Type of organ involvement and severity
		Muscle	Lung	Skin

Dermatomyositis
Anti-Mi2 autoantibodies¹²	Mild-to-moderate muscle involvement with classical skin rash	Moderate	None	Moderate
Anti-NXP2 autoantibodies^13,14	Mild-to-moderate muscle involvement with myalgia, classical skin rash, calcinosis, distal extensor weakness and oedema, and dysphagia; increased risk of cancer	Moderate	None	Moderate
Anti-TIFl autoantibodies^14,15	Strong association with cancer; mild muscle involvement with marked skin involvement, occasionally this type of myositis can present as clinically amyopathic dermatomyositis	Mild	None	Moderate
Anti-SAE autoantibodies¹⁶	Mild-to-moderate muscle involvement with classical skin rash	Mild	None	Moderate
Anti-MDA5 autoantibodies^17–19	Severe skin rash with no muscle involvement (hypomyopathic or amyopathic dermatomyositis) and occasionally highly lethal forms of rapidly progressive interstitial lung disease	None or mild	Severe	Severe
Antibody-negative dermatomyositis²⁰	Mild-to-moderate muscle involvement with classical skin rash	Mild	Unknown	Moderate
Immune-mediated necrotising myopathy
Anti-SRP autoantibodies^21–23	Severe muscle involvement, dysphagia, and 20% of patients with lung involvement with no skin lesions	Severe	Mild	None
Anti-HMGCR autoantibodies^24–26	Exclusive severe muscle involvement; statin-exposed patients	Severe	None	None
Antibody-negative immune-mediated necrotising myopathy	Strong association with cancer	Unknown	Unknown	None
Sporadic inclusion-body myositis^3,27	Older (>50 years) patients with prominant distal and quadriceps involvement; slow progression and refractory to treatment	Severe	None	None
Overlap myositis
Antisynthetase syndrome
Anti-Jo1 autoantibodies^28,29	Mild-to-moderate muscle involvement with progressive lung involvement and possible mild dermatomyositis skin rash (~50% of patients); other characteristic cutaneous features (eg, mechanic's hands and Raynaud syndrome)	Moderate	Moderate	Mild
Anti-PL7 autoantibodies²⁸	Symptoms are similar to those of anti-Jo1 autoantibody-positive myositis with more severe lung involvement	Moderate	Severe	Mild
Anti-PL12 autoantibodies²⁸	Severe lung involvement with mild muscle weakness	Mild	Severe	Mild
Anti-Pm/Scl autoantibodies³⁰	Mild myositis and scleroderma features with muscle weakness, interstitial lung disease, and skin involvement	Mild	Mild	Mild
Anti-Ku autoantibodies³¹	Mild muscle involvement and interstitial lung disease	Mild	Mild	Mild
Anti-U1RNP autoantibodies³²	Myositis, scleroderma, and systemic lupus erythematosus features; glomerulonephritis and pulmonary hypertension are possible	Mild	Mild	Mild
Polymyositis	Diagnosis of exclusion; heterogeneous clinical features	Unknown	Unknown	Unknown

NXP2=nuclear matrix protein 2. TIF1=transcription intermediary factor 1. SAE=small ubiquitin-like modifier activating enzyme. MDA5=melanoma differentiation-associated gene 5. SRP=signal recognition particle. HMGCR=3-hydroxy 3-methylglutaryl coenzyme A reductase. Jo1=histidyl tRNA synthetase. PL7=threonyl tRNA synthetase. PL12=alanyl tRNA synthetase. Pm/Scl=anti-polymyositis-scleromyositis, EXOSC9 and EXOSC10 antigens. U1RNP=U1 ribonucleoprotein. The severity of the organ involvement is based on comparative studies of muscle, lung, and skin involvement in different myositis autoantibody groups.