Neurologists look at myositis from a slightly different perspective than rheumatologists. It's been traditional, since the 1860s when muscle disorders were first described, for them to be covered by neurologists. What we know and do now has evolved over many years of research. Even in the 1960s, we did not distinguish among polymyositis, dermatomyositis, and inclusion body myopathy, as we do now. And we can expect further change in the years ahead in our understanding of these inflammatory muscle disorders.
In the 1960s, trials were done for what was called polymyositis, and the results were presumed to apply to all forms of myositis. One of the first papers reporting the success of corticosteroids, such as prednisone, for polymyositis was published in 1963. The fact that some responded led to the belief that prednisone was effective for all inflammatory diseases of muscle. In subsequent years, we realized the flaws in that study, including the grouping of people with all three diseases. Nonetheless, for many years, all subsequent research used that study as a reference. Today, we know that prednisone is the first line of treatment in certain types of inflammatory disease, but it doesn't always work, especially in disorders such as inclusion body myopathy.
Making a Diagnosis
No one test can make the diagnosis. So how does a "muscle doctor" look at inflammatory muscle disease? Our approach is different from that of the rheumatologist, who usually focuses on antibodies (substances that fight off disease but can attack healthy tissue in auto-immune disease) because there is an antibody response and inflammation occurs.
Neurologists start by taking an individual and family history, often examining other people in the family. That's important because, in contrast to many other muscular disorders, such as muscular dystrophy, none of these three forms of myositis have a family history. So, with rare exceptions, you don't have to worry that you will transmit this disease to your children. Thus, the first step towards diagnosis is looking for a lack of a family history.
We take a history of the onset, course, and distribution of muscle weakness - all important in trying to make a diagnosis.
For example, it would be rare for a person with muscular dystrophy to say "I was well until the spring and then I suddenly had difficulty walking up stairs." Most muscle disorders don't start like that. If you can date the onset of the weakness, it's almost invariably an inflammatory disorder, and that person must be evaluated quickly.
The distribution of weakness is also revealing. Neck extensor muscles (which hold the head back) are generally normal, while neck flexor muscles (which hold the head down) are usually weak in inflammatory disease. Then there's a major distribution in the proximal vs. the distal muscles. The large muscles around the hip girdle and the shoulder are usually weak, with the hands being spared. Sometimes there is difficulty raising the foot. The exception is in older individuals who have inclusion body myopathy, which is now getting to be the most common type of muscular disorder we see in people over 55; patient often complains of falling because the quadriceps muscle in the thigh are usually involved. Further, in inclusion body myopathy, the finger muscles and those that move your wrist down and up can be weak - in contrast to polymyositis and dermatomyositis where hands are okay
So the negative family history, the onset of weakness, and distribution of weakness yield characteristics of inflammatory disease that are different from the many other types of muscle disease.
We also look for skin manifestations. The vast majority of people I have seen in the past five years in whom I have made a diagnosis of dermatomyositis have hardly noticed they had a rash. The rash that to me is characteristic of dermatomyositis is often misdiagnosed in both children and adults. Dermatomyositis is the most common inflammatory muscle disorder that we see in children.
The skin manifestations can come on months to a year before any muscle weakness develops. It can be on the face, hands, elbows, knees, trunk, shoulders - a lot of different distributions. Even though this is not a rare disease, many doctors have never seen dermatomyositis and don't recognize that a rash and muscle weakness signal the disease. However, you can have dermatomyositis without having a rash; sometimes rash never develops.
Next we proceed to testing. As neurologists, we carry our trusted reflex hammer, but it is not terribly important here because reflexes can be very variable in all the muscular diseases.
Most patients are given an EMG - an electromuscular evaluation. It can be a valuable test but can be confusing if not done by someone with experience. When it comes to inflammatory disease, EMGs do not distinguish between dermatomyositis, mixed connective tissue disease, inclusion body myopathy, and polymyositis. All the EMG says is that there's something going on and it looks like an inflammatory disease. Therefore, in some cases, if I am very sure from the clinical aspect what the patient has, I may not order an EMG - although most rheumatologists do.
Rheumatologists also usually order a sedimentation rate, also known as an ESR or sed rate, which may be an indicator of inflammation. But I consider it so non-specific that I don't use it. It can go up even when you have a cold.
The CPK test and other muscle enzyme tests can be very helpful, but they can also be totally normal in about 20% of people with inflammatory disease. In particular, a lot of women who complain of weakness do not get a full evaluation if their CPK is normal, which is a mistake. Another problem is that if you are put on prednisone, the CPK goes down but the patient may not feel better. Or the CPK may be high but the patient may be fine. Heavy exercise, cholesterol-lowering drugs, and other benign issues can raise CPK. There is nothing bad about walking around with a high CPK if you are functionally doing well; it will not cause you any harm. So I do not consider CPK a reliable measurement, especially for following a patient's progress, in inflammatory disease. This is considerably different from the rheumatology approach
Rather, neurologists use muscle testing to follow the patient's progress. In quantitative muscle testing, such as is offered by the laboratory at Hospital for Special Surgery, you may be sitting on a machine or using a grip strength device. I do manual muscle testing in which I have patients hold their arms up and watch them walk.
The final piece in solving the diagnostic puzzle is a muscle biopsy - and preferably an open biopsy rather than a needle biopsy - and the findings are very different in dermatomyositis, polymyositis, and inclusion body myositis. Almost always, the differences will clarify the situation and make the diagnosis for us in the context of the clinical picture. We try to do it in a moderately involved muscle; if we're not sure where to do it, we can do an MRI scan to see the inflammation and target the right spot.
Focus on Dermatomyositis
Dermatomyositis is a disorder that affects the small blood vessels in the muscle, the skin, the gut, and other areas. In children, we also see subcutaneous deposits of calcium; they can be annoying, but we usually don't remove them unless they are in a joint. Typically, they disappear over time. In older people, we look for underlying malignancy. The average activity of dermatomyositis is two to four years - a long disorder and you can have complications from the disease and its treatment. The vast majority of people will have a full recovery, albeit with thin musculature for the rest of life. But it can go into remission and then return later.
Supplements
The jury is still out on the benefits of creatine supplements to build muscle. It is generally harmless, and I advise my patients to take supplements of it, about 5 grams daily. All the sports people take it. However, there are several studies going on to evaluate creatine in various types of myositis, and the evidence still is not in.
Treatment
Prednisone works very well for polymyositis and dermatomyositis, but it does nothing for inclusion body myopathy, again pointing the importance of an accurate diagnosis. If the patient does not respond to the appropriate medication, then the person must be reassessed to reevaluate the diagnosis.
Although prednisone early on came to be the gold standard in treating these diseases, how we use it 40 years later varies considerably. Most neurologists will use a high (80 to 100 mg) single daily dose to start and then, within a week or two, start tapering that dose on alternate days, and then move to the lowest possible alternate day dose. (Rheumatologists often use twice-daily doses.) The determination of how quickly to lower steroid doses and when to discontinue them completely is totally trial-and-error and must be individualized to patient responses. (A study is now under way trying to use pulse steroids in children.)
If the patient does not respond in a relatively short period of time, we reassess the diagnosis. If we continue to feel confident about the diagnosis, we move on to some of the immunosuppressive agents; rheumatologists tend to use methotrexate, but neurologists are more comfortable with azathioprine (Imuran), which most people can tolerate well in relatively high doses, although it can take six months to a year to work. In people with mild dermatomyositis, we have treated them with intravenous gamma globulin alone every three to four weeks. Azathioprine and IV gamma globulin can also help lower the dose of prednisone needed.
For basic pain management, the most common drugs prescribed are celecoxib (Celebrex) and rofecoxib (Vioxx). However, neuropathic pain does not respond to these and other non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen.
Unfortunately, no fully effective regimen has yet been developed for inclusion body myopathy.
For the long term, we hope that stem cell research will provide us with cells that can be transplanted and stimulated to develop into normal muscle.
More about the Myositis Education and Support Group at HSS
Summary prepared by Diana Benzaia.
