The term progressive illness describes the course

Course (medicine)

In medicine, a course of medication is a period of continuous treatment with a drug, sometimes with variable dosage. Treatment with some drugs should not end abruptly...

 of an illness

Illness

Illness is a state of poor health. Illness is sometimes considered another word for disease. Others maintain that fine distinctions exist...

 that gradually progresses and changes mode, generally to the worse. In contrast, non-progressive or chronic illnesses are relatively constant.

Examples

One example of an illness mainly regarded as non-progressive is fibromyalgia

Fibromyalgia

Fibromyalgia is a medical disorder characterized by chronic widespread pain and allodynia, a heightened and painful response to pressure. It is an example of a diagnosis of exclusion...

.

Progressive illnesses are illnesses where the patient can only get worse. Quite a few people suffer from them, and the whole family is affected when someone is diagnosed. Among these are Alzheimer's

Alzheimer's disease

Alzheimer's disease also known in medical literature as Alzheimer disease is the most common form of dementia. There is no cure for the disease, which worsens as it progresses, and eventually leads to death...

and other diseases which elderly people are prone to.