If a rash appears on the extensor surface of the joint, juvenile dermatomyositis may strike quietly!

Author: Li Shipeng, attending physician, Beijing Children's Hospital, Capital Medical University

Reviewer: Deng Jianghong, Chief Physician, Beijing Children's Hospital, Capital Medical University

Xiao Wu is a 3-year-old girl from Ningxia. Her parents found a red rash on the extensor surface of her finger joints one year ago. She visited the local dermatology department many times and considered eczema. The rash improved after applying topical ointment, but it still recurred and there was discoloration at the rash. In the past six months, the child has also had difficulty climbing stairs. She could easily run to the third floor before, but now she feels tired after climbing three or five steps. For this reason, the parents took the child to the rheumatology department of Beijing Children's Hospital. The doctor recognized the child's special rash (Gottron rash) at a glance. Combined with the symptoms of muscle weakness, the doctor told the parents that the child was highly suspected of having a rheumatic disease - juvenile dermatomyositis, and needed to be hospitalized. The child was quickly hospitalized and completed muscle magnetic resonance imaging, electromyography and other examinations. It was finally diagnosed as juvenile dermatomyositis. After active hormone and immunosuppressant treatment, the child's rash and muscle strength improved significantly.

1. What is juvenile dermatomyositis?

Juvenile dermatomyositis (JDM) is an immune-mediated, multi-system disease characterized by acute and chronic non-suppurative inflammation of the skin, skeletal muscle, lungs, and gastrointestinal tract. Its main features are inflammation of small vessels in the skin, muscles, and major organs. Typical clinical manifestations include purple-red eyelid rash, Gottron's sign, symmetrical proximal muscle weakness in the limbs, and significantly elevated muscle enzyme levels including creatine kinase.

Figure 1 Copyright image, no permission to reprint

Gottron's sign (rash on the interphalangeal and metacarpophalangeal joints of both hands)

2. What are the clinical manifestations of juvenile dermatomyositis?

The disease usually presents with fatigue, muscle weakness and rash, and sometimes fever, cough, abdominal pain, dysphagia, muscle pain and arthritis, etc. Some cases have severe systemic symptoms and the disease progresses rapidly, and may die due to combined respiratory failure and heart failure.

1. Rash : Typical skin changes are purple-red macules with mild edema on the upper eyelid or upper and lower eyelids.

The rash may gradually spread to the forehead, bridge of the nose, and maxillary area, and capillary dilation may be seen in the inner canthus and eyelids. Diffuse or localized dark red spots may appear in the "V" area of ​​the neck and upper chest, the trunk, and the extensor side of the limbs. Pigmentation may remain after some rashes subside. Another characteristic skin change is the Gottron sign, which is common on the extensor surfaces of the metacarpophalangeal/metatarsophalangeal joints and interphalangeal/interdigital joints, and may also appear on the extensor side of the elbows, knees, and ankles. The rash is red or purple-red, the size of a soybean, and some may fuse into lumps, which may be accompanied by fine scales. As time progresses, local skin atrophy and hypopigmentation may occur.

2. Muscle weakness : Muscle weakness is the main feature of juvenile dermatomyositis, which usually affects striated muscles. Muscles in any part of the body can be affected. Limb girdle muscles, proximal limbs and flexor muscles of the neck are most often affected, and the proximal limbs and neck muscles are more seriously affected. Edema and nodules appear in the affected muscles in the early stage, and muscle atrophy may occur in the late stage. The clinical manifestations are mainly progressive and symmetrical muscle weakness, which may also be accompanied by muscle pain. Children at the beginning of the disease may show difficulty going upstairs, squatting, dressing, etc., and then develop into difficulty sitting, standing, moving and turning over. Children in the younger age group may only show frequent falls. Weakness of the flexor muscles of the neck is manifested as the inability to flex the neck forward when lying flat, and the "posterior drop sign" is positive. When the eyes, tongue, and soft palate are involved, it can cause ptosis, strabismus, dysphagia, choking, etc. When the intercostal muscles, diaphragm, and abdominal muscles are affected, it can cause dyspnea and endanger life. In the late stage, flexion contracture, limited movement, and dysfunction may occur due to atrophy of muscles around the joints.

3. Involvement of important organs : Severe patients may develop interstitial lung disease, digestive tract and heart involvement,

and calcification.

Figure 2 Copyrighted image is not authorized for reprinting (subcutaneous calcification in a child with juvenile dermatomyositis)

Figure 3 Copyrighted image is not authorized for reproduction (X-ray of subcutaneous calcification)

3. What tests are needed to diagnose juvenile dermatomyositis?

It is necessary to test muscle enzymes, myositis antibodies, muscle magnetic resonance imaging, electromyography, chest CT, gastrointestinal ultrasound, etc., and skin and muscle biopsy are required if necessary.

4. How is juvenile dermatomyositis diagnosed?

The classification scheme and diagnostic criteria for juvenile dermatomyositis developed by Bohan and Peter in 1975 are still used in clinical work.

(1) Typical skin changes include purple-red upper eyelid skin with periorbital edema (sunrise sign) and red scaly rash on the dorsal aspect of the metacarpophalangeal joints and proximal interphalangeal joints (Gottron sign).

(2) Symmetrical proximal muscle weakness, which may be accompanied by dysphagia and respiratory muscle weakness.

(3) Laboratory examination: Elevated serum skeletal muscle enzyme activities, especially creatine kinase and aspartate aminotransferase.

(4) EMG abnormalities: potentials, short-duration multiphasic waves; fibrillation potentials, positive spike waves, prolonged insertion potentials; abnormal high-amplitude discharges at rest, etc.

(5) Abnormal muscle biopsy: muscle fiber degeneration, necrosis, cell phagocytosis, regeneration, basophilic change, enlarged and prominent nuclear membrane, atrophy of perifascial structures, fiber sizes of different sizes, accompanied by inflammatory exudate. If the patient has item (1) and more than 3 of items (2) to (5), he/she can be diagnosed with juvenile dermatomyositis. If item (1) is missing and more than 3 of items (2) to (5) are present, he/she can be diagnosed with polymyositis. This diagnostic standard is simple and practical, but it cannot meet the needs of clinical classification of the disease.

5. How to treat juvenile dermatomyositis?

The main treatment regimen is a combination of glucocorticoids and immunosuppressants: initial treatment uses prednisone/methylprednisolone and methotrexate, etc.; for children with severe illness or high-risk diseases, as well as refractory children, poor response to methotrexate, poor initial treatment effect, or those with adverse reactions, hormones combined with immunoglobulin, cyclosporine A or azathioprine, cyclophosphamide, mycophenolate mofetil and other drugs can be used for treatment. If the condition is still difficult to control, thalidomide, biological agents or JAK inhibitors can be used in combination.

6. What is the prognosis of juvenile dermatomyositis?

Juvenile dermatomyositis is a very heterogeneous disease with a good overall prognosis. Some children have an active disease period of 2 years, which can be completely relieved after treatment. Some children may have multiple relapses or a chronic persistent state, which can last for 3 to 5 years or longer. The most common causes of death from this disease are lung infection, gastrointestinal bleeding and perforation. The most common sequelae are muscle atrophy, tendon contracture and calcification caused by poor control of the disease during the acute phase.

Juvenile dermatomyositis is a relatively rare disease, so parents of children with the disease and many doctors lack knowledge of the disease. However, the disease is serious and can affect important organs. Many children have to go to many places and spend several years to be diagnosed, which seriously affects the prognosis. The main manifestations of the disease are rash and muscle weakness, and the typical rash is a specific Gottron sign, which is easy to identify. If early diagnosis and treatment can be achieved, the child can get a good prognosis. I hope this article can help everyone better understand juvenile dermatomyositis and help children with juvenile dermatomyositis get on the road to recovery as soon as possible.

References

Rheumatology Group of the Pediatric Branch of the Chinese Medical Association, Pediatric Group of the Rheumatology and Immunology Branch of the Chinese Medical Doctor Association, Pediatric Group of the Rheumatology and Immunology Professional Committee of the Cross-Strait Medical and Health Exchange Association, etc. Expert consensus on the diagnosis and treatment of juvenile dermatomyositis[J]. Chinese Journal of Practical Pediatrics, 2022, 37(10).