Types of rheumatoid arthritis
Rheumatoid arthritis can be classified into different subtypes, depending on the genes and molecules involved in the disease process. However, subtyping involves complicated genetic testing and is not performed routinely since it does not affect the diagnosis or treatment of the disease. Subtyping is performed occasionally for research purposes.
Juvenile rheumatoid arthritis is distinct from the adult form. It develops in children under the age of 16 years and can take one of three subtypes:
Pauciarticular juvenile rheumatoid arthritis
This is the most common form of juvenile rheumatoid arthritis, accounting for 40–60% of cases. Symptoms affect no more than four joints initially, although more may be involved later in the course of the disease. The most commonly affected joints are the knees, ankles, wrists or elbows. It is the least severe form of juvenile rheumatoid arthritis.
Polyarticular juvenile arthritis
This accounts for around 40% of cases of juvenile rheumatoid arthritis and is more common in girls than boys. Symptoms develop in five or more joints, often the small joints of the hands or feet although larger joints can be affected. Polyarticular juvenile arthritis is thought to be the same as the adult form of rheumatoid arthritis but occurring at a very young age.
Systemic onset juvenile rheumatoid arthritis
This is the least common form of juvenile rheumatoid arthritis, accounting for around 10% of cases. It tends to develop in children between 5 and 10 years old and presents with non-joint symptoms such as persistently high temperature, rash, loss of appetite and anaemia. Joint and muscle pain often develops later. Systemic onset rheumatoid arthritis can also cause symptoms in the heart, lung or eyes.
