Symptoms of inflammatory myopathy

In dermatomyositis, especially in children, the disease begins with systemic manifestations such as fever and malaise. A characteristic rash then appears, which accompanies or, more commonly, precedes the development of proximal muscle weakness. The cheeks become flushed; a purplish rash appears on the eyelids, especially the upper ones, often accompanied by edema and telangiectasias. An erythematous rash appears on exposed areas of the chest and neck. Discoloration and thickening of the skin is noted on the extensor surfaces of the knees and elbows. An erythematous rash is also found in the area of the interphalangeal joints of the hands. Discoloration of the nail beds is also observed, followed by telangiectasias and edema. Over time, muscle weakness progresses, accompanied by pain and stiffness. The proximal muscles of the upper and lower extremities are involved to a greater extent than the distal ones. Children with dermatomyositis may develop flexion contracture in the ankle joints.

The progression and duration of the disease vary considerably. In children, dermatomyositis may present as an acute attack, ending in recovery even in the absence of immunosuppressive therapy. In others, the disease takes on a remitting course with alternating exacerbations and remissions or a steadily progressive course. With rapid progression, all muscles may be involved, including the muscles of the larynx and pharynx, as well as the respiratory muscles. In approximately 70% of affected children, calcifications are found in the subcutaneous tissues. Mortality in dermatomyositis in children ranges from 5 to 10%.

In adults, dermatomyositis presents with a rash in the malar arches, heliotropic discoloration and swelling of the eyelids, and erythema in the knees, elbows, anterior neck, and chest, as in dermatomyositis in children. Over time, the skin becomes brownish and thickened or depigmented. Skin changes usually accompany or precede the development of proximal muscle weakness. However, cases have been reported in which the skin changes characteristic of dermatomyositis were not accompanied by muscle involvement.

Approximately 40% of adult patients with dermatomyositis develop a malignancy, whereas cancer is much less common in patients with polymyositis. The clinical picture of a malignancy may precede or delay the onset of myopathy. Removal of a tumor, such as an ovarian tumor, may result in regression of muscle weakness. In such cases, the malignancy itself may be life-threatening. The true prevalence of malignancy in patients with polymyositis and dermatomyositis remains unknown, since published reports have included only a small number of patients, and tumor detection may precede or lag behind the onset of myopathy by a year or more.

In polymyositis, the distribution of muscle weakness is similar to that in dermatomyositis, but some other clinical manifestations are different. Polymyositis usually develops gradually over weeks to months, predominantly involving the proximal muscles of the upper and lower extremities. However, muscle weakness can develop with remarkable rapidity. The disease typically develops in the second decade of life, but occasionally occurs in childhood. The eye muscles and facial muscles are usually spared. However, dysphagia is common. The rash characteristic of dermatomyositis is usually absent, but other systemic manifestations, such as arthritis, occur in about 50% of patients with polymyositis. Respiratory dysfunction may be caused by weakness of the respiratory muscles, aspiration pneumonia (a complication of dysphagia), or interstitial pneumonitis. Involvement of the heart with dysfunction of the conduction system, development of cardiomyopathy and heart failure is possible with both polymyositis and dermatomyositis.

Inclusion body myositis is characterized by generalized muscle weakness. It usually manifests itself after the age of 50, more often in men than in women. The diagnosis of inclusion body myositis is often delayed due to the clinical similarity of inclusion body myositis and polymyositis. The hallmark of inclusion body myositis may be early involvement of the distal muscles of the upper extremities with the development of weakness of the flexors of the fingers and atrophy of the muscles of the forearm, as well as involvement of the proximal and distal muscles of the lower extremities with the development of weakness of the quadriceps femoris and extensors of the plantar fascia. One study, which included 21 randomly selected patients with histologically confirmed inclusion body myositis, demonstrated the specificity of involvement of the flexor muscles of the fingers and demonstrated the differential diagnostic value of MRI. In 20 of 21 patients, a relatively specific sign was detected - a heterogeneous increase in the signal intensity of the deep flexor of the fingers on T1-weighted images.

Inclusion body myositis is difficult to diagnose based on clinical data alone. Like polymyositis, inclusion body myositis may present in the second to fourth decade of life and involve the shoulder girdle muscles and facial muscles. Transient myalgias are possible in the early stages of the disease. Clinical signs of peripheral neuropathy in the form of weakened tendon reflexes may be noted. Inclusion body myositis has not been associated with cancer. Even with asymmetric involvement of the flexors of the fingers and extensors of the legs, the most important clinical sign that distinguishes inclusion body myositis from dermatomyositis and polymyositis is the absence of a pronounced response to immunosuppressive therapy in patients with inclusion body myositis. Although most cases of inclusion body myositis are sporadic, familial cases of the disease have been described, with some clinical overlap with hereditary distal myodystrophies. In familial cases of inclusion body myositis, the genetic defect has been mapped to chromosome 9 (9pl-ql), but the nature of the genetic defect has not yet been clarified.

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