I. Etiology
(A) Arthritis with arthralgia
1.Acute arthritis with arthralgia
(1) Trauma: Trauma such as fracture and blood accumulation in the joint cavity causes acute arthralgia, and such cases usually have a clear history of trauma, which can be diagnosed by history taking, joint cavity aspiration, or X-ray examination. Ultrasound examination of the joint can help to distinguish whether the swelling is caused by exudation from the joint cavity or by swelling of the soft tissues around the joint.
(2) Septic arthritis: Most infections occur via blood flow. The diseased joints show redness, swelling, heat, pain and functional limitation, and are more common in large joints. The joint synovial fluid is cloudy, the joint cavity exudate leukocyte count is >5.0 × 109/l, the blood sedimentation is increased, and the bacterial examination is positive. Gram-positive bacteria are the most common pathogens. Synovial fluid examination is rarely positive for pathogenic bacteria. The vast majority of cases involve single joints, and about 4-6% may affect multiple joints.
(3) Osteomyelitis: periarticular pain due to osteomyelitis is sometimes considered acute arthralgia in children and needs to be differentiated. In the early stages of osteomyelitis, bone radiography only shows swelling of the soft tissue around the infected bone. Bone scan is a useful diagnostic method.
(4) Reactive arthritis and post-infectious arthritis: A history of respiratory or urinary tract infection, concomitant conjunctivitis, urethritis, or glottitis in the child before the onset of arthritis helps in the diagnosis. Acute rheumatic fever is an inflammatory disease caused by A beta-hemolytic streptococcal pharyngitis followed by an acute onset of fever and wandering arthritis (pain), with a high incidence of knee and ankle joints and less frequent involvement of small joints of the hands and feet. In recent years, a form of post-streptococcal arthritis has been recognized that presents as prolonged polyarthritis (pain) and differs from rheumatic fever.
(5) Post-enteric arthritis: Children with post-enteric arthritis often have a family history of spondyloarthropathy, and most are HLA-B27 positive. Its clinical manifestation can be transient, severe joint pain, but a few patients can develop chronic arthritis.
2.Chronic arthritis with arthralgia
(1) Systemic juvenile idiopathic arthritis: the main manifestations are fever, rash, enlarged liver and spleen lymph nodes and arthritis.
(2) Juvenile idiopathic arthritis with few joints: within the first 6 months of disease onset, ≤ 4 joints are involved, early childhood onset, with the involvement of large joints in the lower extremities as the main cause.
(3) Polyarticular juvenile idiopathic arthritis (rheumatoid factor+ and rheumatoid factor-): within the first 6 months of disease onset, ≥5 joints are involved, and the clinical features are symmetric polyarthritis, especially the involvement of the small joints of the fingers and toes.
(4) Psoriatic juvenile idiopathic arthritis: psoriasis in which chronic inflammatory disease of the osteoarticular system occurs, with clinical features including oligoarthritis, distal interphalangeal arthritis, asymmetric or symmetric polyarthritis, and medial or spinal arthritis in children with psoriasis. Associated with HLA-B27.
(5) Arthritis associated with attachment point inflammation: attachment point inflammation refers to inflammatory lesions at the attachment points of tendon ends to bone or where tendons, ligaments and joint capsules attach to bone. It manifests as localized pain, swelling, tenderness, or slight redness and warmth. Severe and persistent lesions may result in cortical erosion, hyperplasia, and ankylosis.
(ii) Systemic connective tissue disease
Systemic lupus erythematosus, scleroderma, dermatomyositis, leukoarthrosis, mixed connective tissue disease, polyarteritis nodosa, Kawasaki disease, and allergic purpura may be associated with arthralgia.
(iii) Arthralgia associated with malignant tumors
Leukemia, neuroblastoma and bone tumors may manifest as acute arthralgia. This disease should be considered when the general condition of the child is poor, especially when it is accompanied by anemia, leukopenia and thrombocytopenia, and increased blood lactate dehydrogenase.
(iv) Others
Diabetes mellitus, hemophilia, rickets, growing pains, vitamin C deficiency and mercury poisoning may also be associated with arthralgia.
Differential diagnosis
(A) Take medical history
Learn about the first joint, rapid or slow onset, local manifestations, single or multiple, wandering or fixed, symmetrical or asymmetrical, upper or lower extremities or upper and lower extremities, persistent, transient or recurrent course of the disease, mode of remission and the presence or absence of sequelae. Concomitant phenomena (e.g., fever, sore throat, red eyes, abdominal pain, diarrhea, frequent urination, painful urination, rash, myalgia, and episodic bruising of the fingertips). Tests and treatments received, and response to treatment. Any patients with similar diseases in the family.
(II) Physical examination
1. General examination: A thorough and detailed physical examination can provide important clues to the diagnosis of arthritis. Skin psoriasis, butterfly-shaped erythema, periorbital edema and lavender upper eyelid rash, and taut, hard skin may suggest psoriasis, lupus erythematosus, dermatomyositis, and scleroderma, respectively, associated with arthritis. Oral and genital ulcers and puncture point pustules suggest leukoarthrosis. Circumscribed erythema is associated with rheumatic fever.
2. Joint examination: Every joint should be examined, not limited to the diseased joint. The examination should compare the affected side with the healthy side, or with the healthy joint of the examiner. Abnormal signs of diseased joints.
(1) Swelling: An important sign of arthritis. Swelling can be caused by soft tissue edema, synovial hyperplasia, joint cavity effusion or bony bulge and can be differentiated by examination.
(2) Tenderness: It is a painful response caused by the examiner’s direct finger pressure on the affected joint, and local temperature changes can be palpated. In addition, it should be distinguished whether the tenderness comes from the joint or its surrounding soft tissues. Tenderness around the joint with pain and limitation of joint movement in all directions often indicates joint involvement.
(3) Joint mobility: This refers to the range of active and passive movement of each joint. When the joint structure is damaged, the range of motion of the joint is reduced, or even immobilized.
(C) Auxiliary tests
1.Laboratory tests.
(1) The presence of one or several abnormalities in one or more of the three blood tests can be directly or indirectly helpful in the diagnosis of arthritis. If the arthritis in a patient with leukemia confirmed by blood picture can be diagnosed as leukemic arthritis. Infectious arthritis is considered in those with increased total white blood cells and neutrophils with fever and red, swollen, hot and painful joints. Arthritis with reduced leukocytes and/or platelets should suspect systemic lupus erythematosus.
(2) Blood sedimentation and C-reactive protein are non-specific tests, but they are useful for differential diagnosis and determining disease activity.
(3) Anti-hemolytic streptococcal factor O, rheumatoid factor, anti-nuclear antibody and anti-Ds-DNA antibody are informative to suggest rheumatic fever, rheumatoid and lupus erythematosus, respectively.
2.Imaging examinations.
(1) X-ray film: joint X-ray film can record the abnormalities of the lesion in terms of gross anatomy, reflect the degree of joint damage, the speed of lesion progression and the response to treatment.
(2) Computed tomography (CT): CT is superior to X-ray because of its high resolution and axial imaging, which can clearly show soft tissues, bones and joints, especially the small vertebral joints of the spine, sacroiliac joints and hip joints.
(3) Other: magnetic resonance imaging and ultrasound examination have been used in joint diseases, which can show lesions of meniscus, articular cartilage, ligaments, synovial membrane and joint cavity fluid in addition to bone lesions.
3, arthrocentesis and synovial fluid examination: synovial fluid analysis is one of the important examinations, especially for monoarthritis. Accumulated blood and microorganisms can be found from synovial fluid, which are valuable for confirming the diagnosis of traumatic arthritis and infectious arthritis, respectively.