Polymyositis – symptoms, diagnosis and treatment

Polymyositis comprises of a number of conditions where muscles are damaged by a variety of pathological agents ranging from virus, toxic degenerative or to an autoimmune disorder.

The term polymyositis refers to involvement of muscles while in dermatomyositis, there is in addition involvement of skin. All these conditions are now identified to be of autoimmune origin and these are genetically associated with HLADR.

Polymyositis means inflammation of the muscles and is the most common of inflammatory myopathy. It may be present in primary idiopathic form or associated with dermatomyositis.

The disease starts insidiously and involves all age groups and both sexes, though females Out number males. The peak incidence of the disease is generally in middle age.

The disease generally presents with weakness of muscles especially proximal limb muscles and pain of aching type and tenderness of the muscles. There may be non specific symptoms such as low grade fever, fatigue, weight loss and morning stiffness.

In 25% of cases there is involvement of pharynx and esophagus leading to dysphagia.Significant respiratory impairment occurs in small percentage of cases. As the disease progresses patient finds difficulty in walking and riding stairs.

But there is no involvement of ocular muscles. Cardiac abnormalities in the form of myocarditis, cardiac arrhythmias and even congestive heart failure develops in 25-30% of cases. Distal muscle weakness, may develop at a later stage. Diagnosis of polymyositis is based on:

1. Elevation of enzymes such as C.K., aldolase, SGOT, SGPT and lactic acid dehydrogenase (LDH).

2. Electromyography (EMG): Abnormal

3. Muscle biopsy. There is destruction of muscle fibres with infiltration of inflammatory cells.

4. ECG: Features of myocarditis

Polymyositis

Prognosis and treatment

The disease progresses over a period of weeks to several months and goes into a subacute or chronic form. Prognosis is good if polymyositis is due to idiopathie causes but it is different, when it is associated with collagen disorders, sarcoidosis, and malignancy.

Treatment in acute stage is prednisone 1-2 mg/ kg body weight per day. Patients in acute or subacute form improve rapidly as compared to chronic form of disease. Cytoloxic drugs (cyclophosphamide and methotrexate) are employed when the disease is severe. Majority of patients improve with treatment and make full recovery though some degree of functional weakness may persist.

Acute dermatomyositis

It occurs at all ages but mainly involves children and is characterized by muscular weakness of the proximal group of muscles which become swollen, tender and weak.

The onset may or may not be accompanied by fever but characteristic signs of acute dermatomyositis are skin changes which may precede or follow the muscle weakness. There may be diffuse erythema, maculopapular eruption and dermatitis. There is helitropic rash on the face, chest and extremities with itching which may be troublesome.

Skin lesions are variable and as the disease progresses other group of muscles become involved. Oedema and swelling of the muscles gradually subsides. Other structures in the body like heart and respiratory muscles may be involved.

Characteristic pathological changes are fragmentation of muscle fibers with inflammatory reaction and active phagocytosis. Skin is involved with dermis being swollen and thickened. There is infiltration of lymphocytes, plasma cells etc beneath the epidermis and around blood vessels.

Diagnosis

It is based on muscle weakness with skin lesions. Serum levels of enzymes are elevated. Myoglobin may be found in urine in acute cases indicating muscle destruction. Further confirmation is by electromyography and muscle biopsy.

Treatment is by prednisone 60 mg/per day in divided doses. There is rapid improvement. The drug may have to be continued for long time and slowly tapered off.

Muscular dystrophies

These are a group of muscular disorders which are inherited as X-linked condition characterized by hereditary and familial nature and progressive degeneration of muscles. Each type of muscle dystrophy has its own genetic features and phenotype.