Children's inflammatory myopathy is frequently misdiagnosed, 3 diagnosis and treatment experiences save little lives!

*For medical professionals to read and reference, I want to say that accuracy is not easy, what can I do to save children's lives? With the deepening of people's understanding of myositis-specific autoantibodies (MSA) and myositis-associated autoantibodies (MAA), there are many subtypes of inflammatory myopathy and the characteristics of heterogeneous treatment have gradually surfaced.
Symptoms are confused with many diseases, which brings many obstacles to clinical diagnosis and treatment
.

When children suffer from this disease, early identification is related to the long-term and even life-long prognosis of children
.

How to identify early childhood inflammatory myopathy? Professor Sun Li from the Pediatric Hospital of Fudan University, National Children's Medical Center, made a wonderful sharing at the 2021 Annual Meeting of the Rheumatology and Immunology Branch of the Chinese Medical Doctor Association
.

Accurate identification: how to classify inflammatory myopathy In clinical practice, the disease that begins with "idiopathic" is the most headache for doctors, which may mean that the cause cannot be identified and the appropriate treatment can be selected.
Idiopathic Inflammatory Myopathy (IIM) More so
.

Fortunately, advances in MSA/MAA and muscle biopsy allow IIM to be classified into immune-mediated necrotizing myopathy (IMNM), inclusion body myositis (IBM), polymyositis (PM), and Dermatomyositis (DM), in which DM is further divided into typical DM and clinical amyopathic dermatomyositis (CADM), CADM can be further subdivided into amyopathic DM and hypomyopathy DM (HDM)
.

The mutual correspondence between the IIM antibody profile and the phenotype profile can guide early diagnosis, promote clinical classification, increase prognostic judgment, and profoundly guide treatment
.

Figure 1.
Overview of myositis antibody specificity [1] Special attention to juvenile dermatomyositis: the biggest hidden danger in children's IIM In children's IIM, juvenile dermatomyositis (JDM) is the most common type, accounting for about 50% of the total 85% of children's IIM
.

JDM is a chronic inflammatory myopathy that affects the skin, striated muscle, and other tissues and organs (including the digestive tract, heart, and lungs) in patients aged 0-15 years
.

The annual incidence of JDM is 0.
2-0.
4/100,000 children, with a high incidence in children over 5 years old, and the prevalence of girls is 2-5 times that of boys
.

JDM is insidious to a certain extent, so the misdiagnosis rate is high (delayed diagnosis can be as long as about 10 years).
Among them, myositis (muscle weakness) and cutaneous vasculitis (rash) are the most common manifestations of JDM
.

Different course patterns of JDM have different prognosis, of which 41% have a single course, 59% have multiple courses or chronic status, and MSA-positive patients are more likely to show the latter
.

At present, the treatment of JDM is more dependent on glucocorticoids.
Therefore, early identification and guidance of more targeted treatment to reduce the use of glucocorticoids is the key to improving the prognosis of children with JDM
.

The phenotypes of JDM patients are complex, and MSA-positive patients are more prone to target organ involvement, which eventually leads to the death of the children
.

The current classification criteria of JDM mainly refer to muscle weakness, increased muscle enzymes, myogenic lesions, and muscle biopsy, and it is believed that MSA-related content will also be included in the future
.

Frequent misdiagnosis: What are the causes of misdiagnosis of JDM? Typical manifestations of JDM are rash, decreased muscle strength, Yang sign, Gottron sign, etc.
Atypical manifestations include muscle weakness, joint deformity, V sign, shawl sign, fever, interstitial lung disease , increased liver enzymes, etc.
, so patients may go to the department of rheumatology and immunology, dermatology, liver disease, liver disease, infectious disease, respiratory department and even neuromuscular disease
.

Aimlessness and lack of specialist knowledge are the most fundamental reasons for the misdiagnosis of JDM, which can lead to symptoms including acute and chronic eczema, erythema multiforme, hemophagocytic lymphohistiocytosis (HLH), undetermined fever, and muscle weakness.
Decreased, increased muscle enzymes, cerebral palsy, pulmonary interstitial lesions, bone and joint deformities, and abnormal liver function
.

Specifically: the symptoms of positive rash and erythema butterfly are easily misdiagnosed as systemic lupus erythematosus; some JDMs are misdiagnosed as juvenile arthritis because of malar erythema (drunk appearance) and the rash progresses and retreats with heat; Gottron's sign Children with shawl and shawl sign are easy to be diagnosed with hand, foot and mouth disease; JDM shallow ulcers (auricle, back and arms) and deep ulcers will make the diagnosis ignore symptoms such as muscle weakness (specific manifestations of MD5 antibody positive), thus misdiagnosed as vasculitis; Puffy eyelids and sausage mouth are easily overlooked and misdiagnosed as eye, kidney or cardiac diseases (specific manifestations of NXP2 antibody positive); lipoatrophy and subcutaneous calcification (specific manifestations of NXP2 antibody positive) are prone to long-term delayed diagnosis
.

Figure 2.
JDM-related skin phenotypes Prof.
Sun Li summarized 3 diagnosis and treatment experiences from his team based on case sharing for reference by peers: Dermatomyositis with macrophage activation syndrome (MAS) is not uncommon, and MAS It usually occurs within 3 months of onset (even before the diagnosis of primary disease JDM); MSA examination (especially MD5) should be considered in children with drunken appearance, rash, and shallow ulcers; inflammatory myopathy can also be used as a single Important clues in genetic autoinflammatory diseases
.

Therefore, for the current situation of JDM that is easily misdiagnosed, a multidisciplinary team should be built according to the actual situation, focusing on: children with "eczema" who have not been cured for a long time; children with periorbital edema, skin ulcers, and subcutaneous calcification; fever to be investigated and hemophagocytic Children with predisposition; children with decreased muscle strength and no rash or not paying attention to rash; children with pulmonary interstitial lesions as the first symptom; children with limited joint mobility and subcutaneous calcification,
etc.

The most powerful weapon: how to use muscle biopsy and myositis-specific antibodies for early identification of myositis.
Muscle biopsy is suitable for patients whose myogenic or neuronal damage cannot be identified clinically and electrophysiologically.
Myogenic damage is mainly from hereditary (genetic counseling, judging prognosis, genetic diagnosis) and acquired (defining damage, guiding treatment, selecting typical rash biopsy) should be considered, and the timing of biopsy is best before hormones are used
.

All muscle diseases with weakened muscle strength require a muscle biopsy
.

On the other hand, the detection of MSA is also of great significance for the early identification of many inflammatory diseases, including JDM.
When testing errors are excluded, many MSAs can characteristically represent a certain inflammatory myopathy
.

Figure 3.
Known MSA information and the association between MSA and the clinical phenotype of myositis, which is the basis of MSA as a reliable indicator for the diagnosis of myositis, has also been described in many ways
.

Figure 4.
Correlation analysis between common myositis antibodies and clinical phenotypes in JDM [2] Mastering the correlation between MSA and clinical phenotypes is helpful for early identification of myositis, especially for JDM with different autoantibody manifestations
.

Figure 5.
Association between myositis-specific antibodies and clinical phenotype (CMAS: Childhood Myositis Assessment Scale; ILD-Interstitial Lung Disease; RPILD: Rapidly Progressive Interstitial Lung Disease) Summary of Inflammatory Myopathy in Children It is a disease that has the hope of cure but is accompanied by the risk of death.
If it is not recognized early, the child is very likely to die of lung, digestive tract and other organ involvement
.

For the early identification of inflammatory myopathy in children, although MSA is a reliable detection indicator of the latest progress, its application must be based on clinical findings, rather than using MSA as a census item
.

Due to the lack of specificity of symptoms, the misdiagnosis rate of childhood inflammatory myopathy remains high.
Therefore, doctors need to strengthen their cognition and multidisciplinary teamwork, and rationally use muscle biopsy or molecular diagnosis to improve the diagnosis rate, so as to accumulate more clinical experience, Accelerate accurate diagnosis, help more children, and improve curative effect and long-term prognosis
.

Reference: [1].
Schmidt J.
Current classification and management of inflammatory myopathies[J].
Journal of neuromuscular diseases, 2018, 5(2): 109-129.
https://pubmed.
ncbi.
nlm.
nih.
gov /29865091/[2].
Guan Wanzhen, Li Guomin, Li Yifan, et al.
Association analysis between common myositis antibodies and clinical phenotypes in juvenile dermatomyositis [J].
Chinese Journal of Evidence-Based Pediatrics, 2021,16(2) :93-98.
DOI: 10.
3969/j.
issn.
1673-5501.
2021.
02.
003.
http://med.
wanfangdata.
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