Dermatomiositis Y Polimiositis

Dermatomiositis y poliomiositis

Essentials of Diagnosis * Proximal muscle weakness, elevated serum levels of enzymes derived from skeletal muscle, myopathic changes demonstrated by electromyography, and muscle biopsy evidence of inflammation are diagnostic criteria for polymyositis and other idiopathic inflammatory myopathies. * Dermatomyositis is defined by the additional presence of acharacteristic skin rash. * These manifestations can occur in a variety of combinations or patterns, and no single feature is specific or diagnostic. * The diagnosis is made by fulfilling these criteria in combination and excluding other potential causes for these abnormalities. * Inclusion body myositis is an inflammatory myopathy that must be distinguished from polymyositis,especially in patients 50 years or older. Distinctive features of this disease include an asymmetric pattern of muscle weakness that includes distal muscle groups and characteristic histopathologic features. |

General ConsiderationsInflammatory myopathies are rare diseases. Estimates of incidence range from 2.2–7.7 cases per million. The incidence appears to be increasing, although this may simplyreflect increased awareness and more accurate diagnosis. Six types of myositis are currently classified as "idiopathic inflammatory myopathies" (Table 28–1). Table 28–1. Clinical Classification of the Idiopathic Inflammatory Myopathiesa |
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Polymyositis |
Dermatomyositis |
Juvenile dermatomyositis |
Myositis associated with neoplasia |
Myositis associated with connective tissue disease|
Inclusion body myositis |
|
aIn the past, the terms "idiopathic inflammatory myopathy" and "polymyositis" have been used interchangeably. Today, idiopathic inflammatory myopathy is used to represent the spectrum of these conditions; polymyositis represents one of these diseases. |
These diseases are seen in all age groups, but overall the age at onset has a bimodal distribution withpeaks observed between ages 10 and 15 years in children and between 45 and 60 years in adults. However, the mean ages for specific types of myositis differ. Both myositis associated with malignancy and inclusion body myositis are more common after age 50 years. The age at onset for myositis occurring with an established connective tissue disease is similar to that for the associated condition. Womenare affected twice as commonly as men, with the exception of inclusion body myositis, in which men are affected more often. |

Clinical FeaturesSymptoms and SignsProximal and symmetric muscle weakness is the cardinal clinical feature of the inflammatory myopathies. Muscle pain and tenderness are infrequent. Weakness of the proximal muscles of the legs is usually noted first and results indifficulty arising from a chair or climbing stairs. Weakness of the proximal arm muscles may limit the ability to lift heavy items, to brush one's hair, or to reach up to shelves. Neck and axial muscles are also commonly involved. The detection of muscle weakness on physical examination typically relies on manual muscle strength testing and is usually rated on a scale of 0 to 5. However, thistesting may miss subtle degrees of weakness and not be sufficiently sensitive or objective to detect changes in muscle strength with therapy. Accordingly, functional measurements of muscle strength are often helpful. These include determining how long it takes the patient to arise ten times from a chair without use of the arms or to walk 10 meters. The patient's ability to rise from a squat or stand onhis or her toes and heels can also be assessed.Polymyositis usually has an insidious onset over 3–6 months with no identifiable precipitating event. Pelvic and shoulder girdle musculature are affected most, but weakness of neck muscles, particularly the flexors, is also common. Ocular and facial muscles are virtually never involved. Dysphagia may develop secondary to esophageal dysfunction or...