14	Lung Disease in Systemic Lupus Erythematosus, Myositis, Sjögren’s Disease, and Mixed Connective Tissue Disease	231
a	b

Fig. 14.7  NSIP pattern with ground glass opacities and cystic lesions in the lower lobes in a patient with mixed connective tissue disease (panel a). A progressive decrease of the ground glass and increase in the size and extent of cystic lesions was observed during follow-up (panel b)

anti-RNP antibody titer, presence of anti-Ro-52 antibodies, and no prior arthritis (Table 14.3) [68, 84].

Myositis

Epidemiology

Myositis, also known as idiopathic infammatory myopathies, is a group of rare autoimmune diseases characterized by skeletal muscle infammation, associated with frequent extramuscular signs such as arthritis, Raynaud’s phenomenon, mechanic’s hands, and interstitial lung disease (ILD) (Table 14.6) [85]. Myositis is a heterogenous group of CTDs composed of polymyositis (PM), dermatomyositis (DM), clinically amyopathic dermatomyositis and anti-synthetase syndrome [6, 86].

Due to this highly heterogeneous nature of myositis, along with the lack of clear diagnostic criteria, epidemiological data are scarce. Based on current data, myositis are rare, with a prevalence ranging from 2.4 to 33.8 per 100,000 inhabitants, and an annual incidence ranging from 1.16 to 19 per million worldwide [87].

Pathophysiology

Pathophysiology of anti-histidyl-tRNA synthetase, also known as an anti-Jo1 positive anti-synthetase syndrome, is best described. It can be favored by environmental exposure, such as tobacco, airborne contaminants and mineral particles, or by respiratory tract infections. These factors lead to aggression of lung tissue, and to a break of immune tolerance [88]. Innate immune cells such as NK lymphocytes are unspeci cally activated and release proteolytic enzymes. The release of histidyl-tRNA-synthetase, an antigen that has immune properties, then leads to the recruitment of immune

Table 14.6  The 2017 EULAR/ACR classi cation criteria for adult and juvenile idiopathic infammatory myopathies (IIM)

	Score points
	Without	With
	muscle	muscle
Variable	biopsy	biopsy
Age of onset
Age of onset of rst symptom assumed to be	1.3	1.5
related to the disease ≥18 years and < 40 years
Age of onset of rst symptom assumed to be	2.1	2.2
related to the disease ≥40 years
Muscle weakness
Objective symmetric weakness, usually	0.7	0.7
progressive, of the proximal upper extremities
Objective symmetric weakness, usually	0.8	0.5
progressive, of the proximal lower extremities
Neck fexors are relatively weaker than neck	1.9	1.6
extensors
In the legs proximal muscles are relatively	0.9	1.2
weaker than distal muscles
Skin manifestations
Heliotrope rash	3.1	3.2
Gottron’s papules	2.1	2.7
Gottron’s sign	3.3	3.7
Other clinical manifestations
Dysphagia or esophageal dysmotility	0.7	0.6
Laboratory measurements
Anti-Jo-1 (anti-histidyl-tRNA synthetase)	3.9	3.8
autoantibody present
Elevated serum levels of creatine kinase or lactate	1.3	1.4
dehydrogenase or aspartate aminotransferase or
alanine aminotransferase
Muscle biopsy features-presence of
Endomysial in ltration of mononuclear cells		1.7
surrounding, but not invading, myo bres
Perimysial and/or perivascular in ltration of		1.2
mononuclear cells
Perifascicular atrophy		1.9
Rimmed vacuoles		3.1

When no better explanation for the symptoms and signs exists, these classi cation criteria can be used. It is proposed that a patient may be diagnosed with IIM if the probability exceeds a predetermined cutoff of at least 55%, which corresponds to a score of ≥5.5, or ≥6.7 if biopsies are included

Modi ed table from [85]

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