D89: Other disorders involving the immune mechanism, not elsewhere classified

Disorders involving the immune mechanism, not elsewhere classified, are a group of conditions that occur when the immune system doesn't function normally. These disorders may occur if the immune system actively damages normal cells in the body (as in autoimmune disorders), if it attacks foreign cells normally (but the reaction results in damage to normal tissue), or if it doesn't react strongly enough to dangers (such as infections or cancer). Common symptoms of these disorders depend on the specific condition and can include frequent infections, chronic fatigue, joint pain, and inflammation in different parts of the body. The progression of these conditions vary, some remain stable or improve over time, while others may gradually or suddenly worsen. These disorders can affect any part of the body, as the immune system is integral to the health of every organ and tissue.