Not every medical condition can be diagnosed at first sight.
There are a handful of extremely serious diseases that present such a wide variety of symptoms that it can be nearly impossible to determine what a patient's painful, disabling condition really is.
These diseases have earned the nickname "The Great Imitators" because of their ability to seem like other conditions.
One of the most famous great imitators is the condition Lupus erythematosus.
Lupus erythematosus is actually a collection of similar autoimmune disorders affecting the body's connective tissues, causing symptoms to many of the body's systems.
As with other autoimmune disorders, such as asthma, lupus causes the body's immune system to attack various bodily systems.
Some forms of lupus only affect part of the body, but the most common and most serious form of lupus, called systemic lupus, can affect any part of the body.
When a patient has systemic lupus, it is nearly impossible to predict when and where symptoms will surface.
The disease does not run a set course, but instead,manifests as occasional flare-ups between periods of remission.
Since so many aspects of the disease are unpredictable, sufferers often live with the condition for many years before a diagnosis is reached.
Other diseases that are also considered Great Imitators include multiple sclerosis, which affects the protective sheaths around the axons of neurons in the brain, spinal cord, and nerves.
Since it interferes with the normal functioning of neurons, its effects on the body can be wide-ranging and ambiguous.
Much as with lupus, people with multiple sclerosis suffer from recurring flare-ups.