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Polymyositis/Dermatomyositis

Polymyositis is an idiopathic non-supportive inflammatory disease of the voluntary striated muscles and dermatomyositis is very similar, except it is associated with very characteristic skin findings. Also included in the autoimmune myopathies is inclusion body myositis, although it has not been proven that it is autoimmune but from the information that we have it does appear to be immunologically mediated. But even when you see a patient like this you have to consider possible infections and one common infection that can sometimes lead to inflammatory myopathy is HIV. Depending on where you practice, it may be polymyositis.

The etiology isn’t known. Sometimes these patients do present acutely and the fact that various viral infections, in particular, can trigger muscle pain and sometimes even elevated CPK, has led people to think that an infection is the precipitating event. In fact, in hypogammaglobulinemia patients, echo viral infections sometimes lead to polymyositis or dermatomyositis-like illness. But obviously these patients develop some sort of autoimmune reaction directed against the muscles. In dermatomyositis, particularly in children, there’s an associated vasculopathy and when you look at the muscles under the microscope you see a lot of perivascular inflammation.

As I mentioned before, it is an uncommon disease. Maybe about five cases per million. Of course, once the patient is diagnosed it doesn’t go away. It may get better but they have the disease for life, like many of these chronic inflammatory diseases that rheumatologist - and also a lot of other sub-specialists - deal with and they can be a significant part of your practice depending on where you are located. These diseases are more common in females, similar to many other rheumatic diseases and autoimmune diseases in general. It is most commonly found in middle-aged adults, although dermatomyositis does have a peak incidence in childhood. So about 20% of these patients do have onset in childhood and pediatric rheumatologists, and occasionally I have seen a few kids with this too. Almost all of those patients are dermatomyositis. It is very very rare to find inflammatory myopathy without skin changes.

Two problems with this disease. One is, sometimes it is difficult to make a diagnosis, particularly in the patient who doesn’t have the skin rash. If you are looking at just polymyositis the findings …none of them are diagnostic. None of the laboratory features are diagnostic. So sometimes it is difficult to feel comfortable with your diagnosis, and the other thing is the treatment. It’s hard to gauge activity of the disease sometimes and sometimes it is difficult to know whether you are doing anything for that patient. Is the treatment working, or are they just getting sick from it?

The most common symptom is the proximal muscle weakness, which almost all the patients have that. Sometimes the patients will relate that they initially had trouble climbing up the steps or getting out of a car and maybe raising their arm above their head to reach for things. Often it comes on very gradually, although in occasional patients it can be quite acute just in a few weeks. This will progress. I’ve had patients … I just saw one patient who is a short-order cook, so he was working 14-16 hours a day, and he got weaker and weaker and weaker. Finally one day he just could not get out of bed. He had to call a relative to just get him to the hospital. So he had persisted with this to the point where he really couldn’t do anything. When we saw him in the hospital and he could hardly raise his head off the bed. That’s how much it had progressed, to the point where he thought, "maybe I ought to see a doctor." So some patients put up with quite a bit before they realize that something is really not just going to resolve.

Muscle pain is not as common, and sometimes even on examination there will be tenderness in the muscles, in the same muscle groups. Usually the proximal muscles, the large upper arms, the upper legs. Occasionally neck muscle weakness. Actually distal muscle weakness is not as common. It is usually found in the more severe patients, and the patients who have waited a lot longer. Sometimes it’s actually … in most instances, we would say if you are taking care of a patient you’d want to have a very attentive the family, but with this disease sometimes this is an impediment to diagnosis because the patients get a lot of care at home and it really gets to the point where the family can no longer take care of them before they bring them in.

Dysphasia and dysphonia can occur because of abnormalities of the pharyngeal muscles, the muscles that regulate the palate. And these are actually two poor prognostic findings, if a patient gives a history of this or if you notice that their voice is very nasal when you are talking to them. Raynaud’s phenomenon, skin rashes really, associated with dermatomyositis only. Skin tightness exhibited by sclerodactyly can be found in a small percentage of these patients. Also, arthralgias and arthritis can be found in about one-quarter and that may be why the patients were first seen by a rheumatologist. I have no idea.

Now when you see a patient with proximal muscle weakness you have to think of a number of other things. I’m just going to go over a few of these. Obviously, other connective tissue disease can be associate with the myositis, particularly in an older person you would be thinking polymyalgia rheumatica because the symptoms can be very very similar. Although most patients with polymyalgia rheumatica complain of rather sudden onset of symptoms. Often they can date the hour that it started. Whereas patients with an inflammatory myositis, like polymyositis, it’s more gradual. They would say it’s been there for a few weeks or months more typically. Also thyroid disease and other endocrine disorders.

Occasionally certain medications like AZT for instance. I don’t know how much it’s used anymore. They’ve come out with so many anti-retroviral drugs, I guess they still use it in some patients. But that is associated with a myopathy and again, certain infections such as HIV as I mentioned before. Also neurologic disorders; ALS sometimes can come on rather suddenly. Patients often present in a fairly late stage and since it has upper and motor neuron damage the patients may have some proximal muscle weakness. It can be kind of a mish-mash and initially it may be something that needs to be considered.

Some of the drugs that are used to treat hyperlipidemia, like clofibrate, which I assume is almost never used anymore, can cause it. I’m not aware that the statin drugs cause a myopathy. I just reviewed the literature and there’s nothing that I came across. I guess it’s been reported. The question is, these are really commonly used drugs and what’s the specific association. But there is a number of other drugs that can cause … I mean there are probably 20 or 30 drugs that can cause a myopathy. But even the drugs that do cause a myopathy.

Now, inclusion body myositis, which is very uncommon - in fact, I just saw my first case, a person who was already diagnosed. He was admitted to the hospital for some other reason and we were asked to see him to make sure his medications were okay. It is clinically similar to polymyositis, but here are some of the differences; the patients are generally older men. Usually it’s a very gradual onset and it may also affect distal muscles to the same degree. The muscle biopsy is very similar to polymyositis, just showing some chronic inflammatory changes and destruction of the muscles. But if you do electron microscopy you see inclusion bodies. This was one of the pieces of evidence initially that made people think of a viral infection as the cause.