A question was asked about whether steroids were just hiding the disease and this is the reply I wrote to try to explain the background in easy to understand language:
GCA (Giant Cell Arteritis) is the name given to the process in the disease that gives rise to the symptoms. The arteries are inflamed - the inflammation isn't significantly different from any other sort, like that with an insect bite. When tissue is inflamed the blood flow increases to the area to remove the problem and that makes it swell up. In GCA special types of cells (very large ones, the giant cell bit of the name) develop in the layer of the artery wall that makes the blood vessel stretchy so that the swelling may become enough to restrict the blood flow THROUGH the blood vessel (rather than TO it). Inflammation often causes fluid retention around the affected area, another part of the body's attempt to get rid of the cause.
In the case of PMR the name is just a description of the symptoms - poly = many, myalgia = painful, rheumatica = to do with muscles - which are probably due to a similar restriction of the blood flow but in other parts of the body. GCA that causes blindness affects the temporal artery which is part of the pathway of blood to the optic nerve. GCA can be in many other arteries but the temporal arteritis bit is the common image we come across, apart from anything else the temporal artery is easy to get at and biopsy to see what they can find. However - only about half of patients with GCA symptoms actually have these cells to be found in the temporal artery.
No-one really knows the exact reason for the giant cells developing in the first place - it is assumed by most authorities that it is an autoimmune action by the body where it attacks its own tissue thinking there is something wrong. On the other hand - the body may well know something we don't and is attempting to rid our body of something that is hurting it that hasn't been identified.
Once you are on steroids the inflammation is reduced - the more there is the higher the dose you need or the longer you need to be on it before it is fully under control. Since in this case you can't SEE the inflammation you have to look at things that might be related to it to see how it is being got under control. It is accepted that ESR and CRP measurments represent that - high when there is a lot of inflammation present in the body and falling as it gets better. Unfortunately, they are very non-specific - that means lots of things affect them, including pregnancy in fact! More than a fifth of patients with GCA and PMR never have had raised levels of either, others have an abnormal reading for one and not the other. So the real situation is that the symptoms must be taken as the guide as to whether you are on the right dose - ahead of any blood levels.
Yes, you are quite right in thinking that the disease is only hidden by the steroids. The steroids deal with the effect of what is going on in the body, if the autoimmune process hasn't died away all that will happen if you reduce the steroids is that the inflammation is allowed to re-emerge and the symptoms start up again. This is a disease without any known cure - it can be managed to allow you a relatively pain-free and normal life by taking steroids, nothing more than that. It's like high blood pressure - just because you have a normal blood pressure when taking your medication doesn't mean you don't have a problem that would cause high blood pressure. The cause is being controlled as long as you take the tablets - stop taking them and your blood pressure will rise again. The tablets just stopped what was causing the symptom of raised blood pressure - it is a sign that something is wrong, it could be one or more of many things.
The difference between people who have it for a long time or a short time is that the underlying thing may have gone away and so the inflammation is no longer being caused. I have also written an analogy to try to explain how it works - it's on here too. I likened it to a forest fire. You can deal with that in various ways that are similar in effect to using steroids. If you spray the fire with enough water the fire will go out eventually when everything is too wet to burn. If you use other substances and remove the oxygen the fire will die away on the surface and maybe go out eventually when there isn't enough oxygen right down deep. If you don't use enough or you don't wait long enough the embers of the fire may still be hot enough to burst back into flame if you scratch at the surface of the covering and expose live embers.
It is possible that you could get rid of GCA altogether by giving a massive dose of steroids, no-one knows as that sort of dose would do so much damage to you. You could cure almost all cancers if you gave enough chemotherapy - but the patients would die of the side-effects. The trick is to get the balance right.
In PMR, there is little risk of you going blind and it is also very unlikely you will die of PMR - so you get a lower dose to start with and then look for the lowest dose that keeps the symptoms under control so you can keep taking it for a long time if necessary without the total dose you take being too massive.
In GCA the stakes are higher: if specific arteries are affected there is a risk of you going blind and so the initial doses are much much higher, especially if you go to the doctor already complaining of visual symptoms or headache. They can't tell how bad the situation is except by the blood values if that applies to you - so once you start to reduce the dose you need to be very careful to note any return of the symptoms that sent you to the doctor in the first place.
If you reduce in very small steps you are more likely to have only very minor symptoms if the dose gets to a low enough level to allow the inflammation to start up again - which is why many of us say to try that so you can remain on that dose for a while. If the step was too big, the inflammation can really get going again - after all, 35mg may be enough to deal with it but 33mg isn't, but you dropped to 30mg so the wind really got up again - just like with a forest fire.
It may be that if you then remain on that dose for a month or more you can try a reduction and get lower, the amount of inflammation has reduced further in the meantime, it just took longer to get there.
Many doctors are only used to using pred for shortterm use - in asthma or exaccerbations of other diseases. They give a highish dose for a few days and then get the patient off quickly. They find it difficult to adjust to these 2 illnesses where the need is for much longertem use with very small adjustments to find a longterm dose.
Hope this helps explain some bits better,
GCA OR STIFFNESS FROM PMR
PMR - increased risk of GCA
Pmr/gca or myosthinia gravis? 
Worried about PMR & GCA
