Some of the gene abnormalities found in PBL include: 1) increased expression  of the MYC proto-oncogene due to its rearrangement with an antibody gene by genetic recombination or, less commonly, other causes (Myc protein, the product of this gene, enhances cell proliferation, inhibits apoptosis, and promotes malignancy); 2) loss in the expression of the PRDM1 gene whose product, PRDM1/BLMP1 protein, represses the expression of Myc protein;) 3) frequent duplications in certain areas of chromosomes 1, 7, 11, and 22 (these duplications are similar to those often seen in diffuse large cell lymphoma); 4) reduced expression of at least 13 genes that are involved in B-cell responses to signaling agents. 5) increased expression of genes which promote the maturation of B-cells toward plasma cells (e.g. CD38, CD138, IR4/MUM1, XBP1, IL21R, and, as just indicated, PRDM1); and 6) reduced expression of genes characteristic of B-cells (e.g. CD20 and PAX5). Diagnosis
Microscopic examination of involved PBD masses and infiltrates generally reveals diffuse proliferations of immunoblast-like cells with prominent features of plasma cells, i.e. plasmablastic cells. Immunostaining of these cells indicate that they lack B-cell marker proteins (e.g. CD20 and PAX5 [in ~10% of cases CD20 may be expressed at very low levels]) but rather express plasma cell marker proteins (e.g. CD38, CD138, IR4/MUM1, XBP1, IL21R, and/or PRDM1). The abnormalities in gene structures and expressions reported in the Pathophysiology section, particularly rearrangement and/or over expression of the MYC proto-oncogene, may also be apparent in these cells.
A common symptom of this type is a high, spiking fever of 103 °F (39.4 °C) or higher, lasting for weeks or months, and a rash of pale red spots on the chest, thighs or other parts of the body may be visible. Cause
In most cases, juvenile arthritis is caused by the body attacking its own healthy cells and tissues, i.e. autoimmunity, causing the joint to become inflamed and stiff. Once the joint has become inflamed and stiff, damage is done to the joint and the growth of the joint may by changed or impaired. The underlying cause in the malfuction of the autoimmune system is unknown; dietary habits and emotional state seem to have no effect on the disease. Diagnosis
Early diagnosis and treatment by a paediatric rheumatologist or a rheumatologist can help manage inflammation, relieve pain, and prevent joint damage. However, it is difficult for doctors to diagnose the disease. Careful examination, laboratory tests (blood and urine), and various forms of imaging like X-rays may be some of the tests conducted by a doctor. Doctors may perform some of the following tests to diagnose the condition
ANA (Antinuclear Antibody) Test
Joint Aspiration
Rheumatoid Factor (RF) Test

Treatment
The treatment of juvenile arthritis includes medications, physical therapy, splints and in severe cases surgery. Methotrexate is commonly prescribed to children with juvenile arthritis. These treatments are focused on reducing swelling, relieving pain and maintaining full movement of joints. Children are encouraged to be involved in extra-curricular activities, physical activity when possible, and to live a "normal" life.