Rheumatoid disease is a relatively common systemic connective tissue disease, the main clinical manifestations of which are longer-term irregular fever, and large, medium and small joint swelling and pain (especially the small joints of the fingers and toes), which can form joint deformities over time, often accompanied by sunset, spleen and generalized lymph node enlargement, anemia and increased autocytes. The younger the child is, the more the clinical manifestations are oriented toward systemic symptoms, while older children or adult patients are more often limited to joint symptoms. Therefore, it is often called rheumatoid disease in pediatrics, which is a more comprehensive name than the previously used “rheumatoid arthritis.
There are still more differences between pediatric rheumatoid disease and chronic rheumatoid arthritis in adults. For example, the mouth has more systemic manifestations (flaccid fever, rash, enlarged liver and spleen lymph nodes, a significant increase in the total number of white blood cells, etc.), while the joint lesions are lighter, occasionally complicating iridocyclitis, pericarditis, cervical spine involvement, etc.; on the other hand, pediatric subcutaneous nodules are less common, and the rheumatoid factor positivity rate is lower.
Etiology
The cause is not fully understood, but is generally considered to be related to allergic reactions and autoimmunity. It may be due to persistent infection by viruses, mycoplasma or other pathogens that cause the denaturation of its own lgG to become an antigen, stimulating the body to produce the so-called rheumatoid factor antibodies, which belong to the IgM class. One molecule of rheumatoid factor in the serum combines with five self-antigen IgG to form a complex, which has all the characteristics of an antigen-antibody reaction and deposits in the tissues of the body, especially in the joints and synovial membranes, later activating complement, attracting neutrophils and releasing enzymes (proteolytic enzymes) from their lysosomes, causing damage to the basement membrane of blood vessels and adjacent tissues, including synovial membranes.
Pathology
The pathological changes of the disease occur primarily in the joints, but may also involve other areas of connective tissue. The synovial membrane within the joint is first invaded, with early congestion, edema and lymphocytic infiltration, followed by thickening of the synovial membrane in the form of villi, and finally granulation tissue. The soft tissues around the joint are also swollen. As the inflammation continues to develop, the granulation tissue starts from the synovial membrane at the edge of the articular cartilage and gradually extends to the cartilage surface, eventually covering the cartilage surface and blocking the cartilage from taking in nutrients from the bursal fluid. At the same time, lymphocyte infiltration and granulation tissue formation in the bone marrow under the cartilage peeled off the cartilage. Eventually, the granulation tissue on the cartilage surface becomes fibrotic or even ossified, causing the upper and lower joints to fuse and become tense. The bones near the joints are decalcified and osteoporotic, the muscles are atrophied, and the joint capsule and ligaments can be invaded by granulation tissue, causing joint dislocation. Subcutaneous nodules, myocarditis, pericarditis, and iridocyclitis may also be seen.
Clinical presentation
It can occur at any age, but is most common between the ages of 2 and 4 and 8 and 10. There are more females than males.
The onset of the disease can be divided into three types.
I. Systemic type (Still’s disease)
Most often seen in young children, both sexes can get the disease. The main manifestations are fever, rash, arthritis and other symptoms of organ involvement. The fever is flaccid, with one or two peaks in a day, with high fever up to 40℃ or more, and daily fluctuations of 3-4℃. The fever may be accompanied by chills before the fever. The child’s condition is generally better after the fever subsides. The fever may last for weeks or months and often resolves spontaneously, but is prone to recurrence.
The rash is polymorphic, with scattered erythematous patches of varying size, occasionally fusing into patches, or in a circular pattern.
The symptoms of arthritis are generally mild, mostly manifesting as polyarticular involvement, but there are also no joint symptoms at all. Most children have enlarged liver, spleen and lymph nodes of varying degrees. In a few cases, there may be pleurisy, pericarditis or myocarditis.
Multiple joint type
This type is similar to adult-type rheumatoid arthritis, with only one to two joints involved at the beginning, wandering in the early stages, and gradually becoming fixed symmetric polyarthritis. It is characteristic of this type that it mainly affects small joints, the proximal interphalangeal joints are most frequently affected, followed by the metacarpophalangeal and toe joints. The onset of this type of disease is mostly slow, with a few cases of rapid onset. At the beginning of the disease, there is localized soreness and morning stiffness, and later the joints become swollen, hot and painful, and gradually become pike shaped, with restricted movement and fixed flexion of the knee, elbow, finger and wrist. In a few cases, the joint is painful but not swollen or swollen but not painful. The muscles near the joint spasm, followed by atrophy, and eventually deformation and ankylosis of the diseased joints, joint deformation is usually seen six months to a year after the onset of the disease, when the pain is reduced. If other parts of the body such as cervical joints are involved, it may cause neck pain and ankylosis, and temporomandibular joint involvement often causes mastication disorder.
Systemic symptoms are mild, with only low fever, fatigue, decreased appetite, mild anemia and mild enlargement of the liver, spleen and lymph nodes.
A small number of children have subcutaneous nodules near the joints. Rheumatoid factor may be positive.
Single joint type
Only a few joints are involved (often one), mainly in large joints such as knee, ankle, elbow, etc.
The joints may show a chronic inflammatory process or recurrent attacks, but rarely cause severe limitation of joint movement. A few cases of this type may have iridocyclitis in conjunction with or after joint involvement, which sometimes becomes the first symptom of the type. Systemic symptoms are mild and may include low-grade fever, weakness, mild anemia and enlarged liver and spleen lymph nodes.
Laboratory tests.
Most of them have moderate anemia during the active period, and the total white blood cell count varies, most of them are increased or normal, especially in the generalized type, up to 60,000-70,000/mm3, and even leukemia-like reaction. Blood sedimentation is significantly increased, C-reactive protein is mostly positive, mucin assay is increased, anti-streptococcal hemolysin “O”, generally not high. Serum proteins are normal or slightly elevated, often due to increased o. Globulins and gammaglobulins, while albumin is mostly decreased.
Immunoprotein electrophoresis: shows increased IgG, IgA and IgM. Antinuclear antibodies are positive.
Rheumatoid factor test: As mentioned earlier, rheumatoid factor in the patient’s serum can only react with denatured IgG. The IgG is generally adsorbed onto latex or sensitized sheep red blood cells in order to make this change in IgG, structure. There are two ways to determine rheumatoid factor using this principle: ① sensitized sheep red blood cell agglutination reaction. ② rheumatoid latex agglutination test. In adults with chronic rheumatoid arthritis, the positive rate is high, up to 80%, while the positive rate in children is low, about 10-20%. However, in other connective tissue diseases such as systemic lupus erythematosus and scleroderma, the rheumatoid factor test can also be obstructive. Therefore, a positive test should be combined with clinical diagnosis, and a negative test cannot exclude the disease.
X-ray examination: Generally, the soft tissue near the joint is swollen, the joint space is narrowed, the joint surface of the bone end is uneven, and there may be small cystic translucent areas under the joint surface (mostly in children in the late stage), and finally the two bones and joints become bony fusion and the joint space disappears. The bone is generally sparse, especially at the bony end of the lesion. In addition, periosteal reaction and joint subluxation are also seen.
Course of disease
The course of the disease varies widely. Occasionally, a short acute attack is followed by a complete recovery. In a minority of children, the symptoms disappear after an acute phase of 2 to 3 years without sequelae. Most children have alternating remission and recurrence of joint symptoms, which may be mild or severe at times. Sometimes the disease may recur even after years of remission.
Diagnosis
If a child has a long lasting symmetrical polyarthritis with predominantly small joints, which eventually leads to the typical symptoms of joint deformity, the diagnosis is generally not difficult. However, the systemic type is more common in children, especially in young children, who may have only fever without obvious joint symptoms, which can be easily misdiagnosed. Therefore, the disease should be considered if there is prolonged intermittent fever, transient polymorphic rash, enlarged liver and spleen lymph nodes, and increased total white blood cell count, and no foci of infection can be found. If the child is found to have joint stiffness in the morning and the symptoms are relieved after much activity, it may help the diagnosis. Further laboratory tests and bone and joint X-rays should be performed to confirm the diagnosis.