This is an inflammatory myopathy characterized by inflammation in the muscles leading to weakness in the affected muscles.
The main difference between Dermatomyositis and Polymyositis is presence of a skin rash. Hence the term Dermato- myositis (dermato = skin, myo = muscle, itis = inflammation) versus Poly-myositis (Poly = many, Myo = muscle, itis = inflammation).
The hallmark of these illnesses is significant muscle weakness in the proximal group of muscles meaning the group of muscles nearer the trunk. Hence thighs arms are affected along with muscles of the shoulder and pelvic girdle, back, neck etc.
As in many other rheumatic diseases, here also women tend to be more affected than men by this illness.
Usually these illnesses come on gradually and there may be muscle pains and tenderness which is gradually progressive in intensity. Most patients will have fatigue. Some will also have lack of appetite, weight loss and fever.
In some patients intercostal muscles (muscles between the ribs which help in breathing, by expanding the chest wall) may be involved causing breathing difficulty. Additionally this disease can also have associated inflammation in the lungs known as interstitial lung disease (ILD). Either one or both in combination if not treated in time can lead to respiratory failure which constitutes an emergency requiring hospitalization in the ICU and ventilation.
In others the muscles of the pharynx may be affected causing difficulty in swallowing. At times the esophagus or the food pipe is also affected causing reflux. This can result in aspiration of food leading to a life threatening Pneumonia.
The skin rash of Dermatomyositis is typical with raised areas which are scaly red, scaly in appearance. This is present over the knuckles and the elbows and front of the knees and is known as Gottrons Papules.
Red rash often affects the face as well and is hard to miss. Quite often this rash is present over back of the neck as if a red shawl is covering the area hence called the “shawl sign”.
The rash also commonly occurs over the upper chest over the exposed part in the shape of the alphabet “V” hence the “V sign” etc.
A purplish discoloration around the eyelids is called “heliotrope” and is another classical feature.
DM/PM can occur along with other rheumatic disease as well making their management all the more difficult.
DM/PM can also be associated with Malignancy and in fact may be the presenting feature at times particularly in women above the age of 40 years and should be actively looked for in this age group. The malignancies commonly associated are of the genitourinary tract (meaning breasts, ovaries, Uterus etc).
Sometimes malignancy can manifest after the onset of this disease and hence periodic investigations this out is mandatory particularly if the disease does not seem to be responding despite using the best of treatment available currently. In other words the disease is refractory to treatment.
The diagnosis of this group of disease is based on certain criteria: 1) The main clinical feature is weakness of the shoulder and pelvic girdle muscles along with involvement of either the lungs or the gastrointestinal tract or both. 2) Presence of typical rash as described above in cases of Dermatomyositis. 3) Abnormalities in the levels of enzymes of the muscles such as the CPK, LDH, SGOT, SGPT, Aldolase. 4) Evidence of muscle weakness on a test called the EMG/NCV ( Electromyogram and nerve conduction studies) 5) Presence or absence of other connective tissue disease such as SLE or Sjogrens syndrome etc. 6) Radiology in terms of an MRI of the muscles may be helpful in confirming the diagnosis by showing inflammation in the muscles which have been imaged. 7) Biopsy of one of the areas out of the affected muscle followed by examination of the tissue will confirm the diagnosis.
The initial treatment of these diseases begins with cortico steroids at relatively higher doses to cut off the process of on-going inflammation before the muscles get damaged by the inflammation in the muscles.
Additionally Immunosuppressants such as Methotrexate, Azathioprine, cyclosporine Mycophenolate Mofetil etc. are added to the steroids simultaneously since their effect will only begin after about 6 weeks of treatment after which, gradual tapering of the dose of steroids can begin. Hence Immunosuppressants are also called steroid sparing drugs as they help in reducing the dose of the steroid while simulating their effect.
Sometimes the immunosuppressants are unable to control the disease entirely in which case Intravenous Immunoglobulins are given in a hospital setting. These are very effective in the treatment of DM/PM but are quite expensive.
Sometimes Plasmapheresis is also done which is a process by which the blood of the patient is filtered to remove the antibodies and thus the components of inflammation from the blood which may help in controlling the disease process.
In case of involvement of the internal organs such as the oesophagus, heart or the lungs appropriate supportive treatment would need to be initiated.
Finally once again here also, Physiotherapy exercises are invaluable and their usefulness cannot be overemphasized. Inflamed muscles remain weak even after the inflammation has been treated adequately and physiotherapy will help these. Additionally toning the unaffected muscles will compensate for the lost power in the affected muscles.
DM/PM can be a devastating disease if treatment is not started on time. In case of organ involvement such as the lungs, oesophagus or even the heart the outcome is quite poor. Malignancy should be ruled out in every case, with extensive investigations at the onset itself and at periodic intervals even after starting treatment because malignancy can manifest after onset of the DM/PM.
Having said the above, the outcome of this disease has significantly improved, in the last few years, with the advent of newer modalities of treatment mentioned above.