Childhood arthritis (also known as juvenile arthritis, JRA, Juvenile Idiopathic Disease or Arthritis, or Stills Disease) is any form of chronic arthritis or chronic arthritis-related conditions which affects individuals under the age of 16. Most types are autoimmune disorders. Signs and symptoms
Several types of childhood arthritis exist, the most common being juvenile idiopathic arthritis (JIA), also known as juvenile rheumatoid arthritis (JRA) or juvenile chronic arthritis (JCA). Other types of childhood arthritis include juvenile myositis, juvenile lupus, juvenile scleroderma, vasculitis, and fibromyalgia.JRA again can be divided into three main forms: The classification is based upon symptoms, number of joints involved and the presence of certain antibodies in the blood. Polyarticular arthritis is the first type of arthritis, which affects about 30–40% of children with arthritis and is more common in girls than boys. Typically five or more joints are affected (usually smaller joints such as the hands and feet but many also affect the hips, neck, shoulders and jaw). Oligoarticular (aka pauciarticular) arthritis can be early or late onset and is the second type of arthritis, affecting about 50% of children with juvenile arthritis. This type affects fewer than four joints (usually the large joints such as knees, ankles or wrists) and may cause eye inflammation in girls with positive anti-nuclear antibodies (ANA). Girls younger than eight are more likely to develop this type of arthritis. Systemic disease is the least common form, with 10–20% of children (boys and girls equally) being affected with limited movement, swelling and pain in at least one joint.
The canonical definition of this disorder precludes permanent weakness in the definition of this disorder. In practice, however, this has not been strictly adhered to in the literature. Pathophysiology
Paramyotonia congenita (as well as hyperkalemic periodic paralysis and the potassium-aggravated myotonias) is caused by mutations in a sodium channel, SCN4A. The phenotype of patients with these mutations is indicated in Table 1. These mutations affect fast inactivation of the encoded sodium channel. There are also indications that some mutations lead to altered activation and deactivation. The result of these alterations in channel kinetics is that there is prolonged inward (depolarizing) current following muscle excitation. There is also the introduction of a "window current" due to changes in the voltage sensitivity of the channel’s kinetics. These lead to a general increase in cellular excitability, as shown in figure 1. There has been one study of a large number of patients with paramyotonia congenita. Of 26 kindreds, it found that 17 (71%) had a mutation in SCN4A while 6 (29%) had no known mutation. There is no large difference between these two groups except that patients with no known mutation have attacks precipitated less by cold but more by hunger, are much more likely to have normal muscle biopsies, and show less decreased compound muscle action potentials when compared to patients with known mutations. Diagnosis
Diagnosis of paramyotonia congenita is made upon evaluation of patient symptoms and case history. Myotonia must increase with exercise or movement and usually must worsen in cold temperatures.