Hyperalgesia ( or ; hyper from  Greek ὑπέρ (huper, “over”), -algesia from Greek  algos, ἄλγος (pain)) is an abnormally increased sensitivity to   pain, which may be caused by damage to nociceptors or peripheral nerves and can cause hypersensitivity to stimulus. Prostaglandins E and F are largely responsible for sensitizing the nociceptors. Temporary increased sensitivity to pain also occurs as part of sickness behavior, the evolved response to infection. Types
Hyperalgesia can be experienced in focal, discrete areas, or as a more diffuse, body-wide form. Conditioning studies have established that it is possible to experience a learned hyperalgesia of the latter, diffuse form. The focal form is typically associated with injury, and is divided into two subtypes:

Primary hyperalgesia describes pain sensitivity that occurs directly in the damaged tissues. Secondary hyperalgesia describes pain sensitivity that occurs in surrounding undamaged tissues.Opioid-induced hyperalgesia may develop as a result of long-term opioid use in the treatment of chronic pain. Various studies of humans and animals have demonstrated that primary or secondary hyperalgesia can develop in response to both chronic and acute exposure to opioids. This side effect can be severe enough to warrant discontinuation of opioid treatment. Causes
Hyperalgesia is induced by platelet-activating factor (PAF) which comes about in an inflammatory or an allergic response. This seems to occur via immune cells interacting with the peripheral nervous system and releasing pain-producing chemicals (cytokines and chemokines).One unusual cause of focal hyperalgesia is platypus venom.Long-term opioid (e.g.
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.