Overview of Inclusion Body Myositis
Inclusion body myositis (IBM) is an inflammatory myopathy characterized by the presence of rimmed vacuoles in the submuscular membrane or in the center of muscle fibers under light microscopy, and the presence of tubular filamentous inclusion bodies in the myoplasm or nucleus of the muscle under electron microscopy, which progresses slowly and has a specific location in the affected muscle, which may be related to immune-mediated or may be a muscle degeneration disease. IBM is the most common inflammatory myopathy in people over 50 years of age, and can occur in both sexes, but is more common in middle-aged and elderly men, with a male to female ratio of 3:1.
Etiology
The pathogenesis of this disease is unclear, but it may be an immune-mediated, multifactorial, genetic susceptibility-associated muscle degenerative disease with a secondary inflammatory response.
Symptoms
The disease is often of insidious onset, with chronic progression, and is characterized by painless muscle weakness and atrophy. Proximal or distal muscles may be involved, with the quadriceps being the most commonly involved. Patients start with unilateral or bilateral localized muscle weakness, such as quadriceps, finger flexors, wrist flexors, or dorsiflexors of the foot, which then extends to other muscle groups within months or years, with selective muscle weakness of the flexor digitorum longus being the most characteristic. About 1/3 of the patients have facial muscle weakness, and most of the extraocular muscles are not involved. Due to the involvement of pharyngeal muscles, many patients may have dysphagia. Physical examination reveals atrophy of the forearm muscles and quadriceps with loss of knee reflexes, while other tendon reflexes are initially normal, but may be weakened with the progression of the disease. In a few patients, cardiovascular disease may be combined.
Examination
1. Laboratory examination
Serum CK can be normal or elevated several times, but not more than 12 times the upper limit of normal value; erythrocyte sedimentation rate is normal. Serum immunoglobulin and autoimmune indexes are not abnormal.
2. Electromyography
Suggests myogenic and neurogenic damage.
3. Muscle biopsy
It shows that the size of muscle fibers varies, atrophic muscle fibers are small rounded and small angular shape, and necrosis of muscle fibers can be seen, especially more muscle fibers can be seen to appear rimmed with vacuoles and more basophilic granules, and monocytes can be seen to infiltrate the non-necrotic muscle fibers. Electron microscopy reveals tubular filamentous or medullary inclusions under the myofibrils or in the nucleus.
Diagnosis
1. In patients over 50 years of age, the disease has a chronic course, with weakness of the proximal and distal extremities, as well as dysfunction and muscle atrophy, especially of the quadriceps;
2. laboratory tests showing moderately elevated serum CK levels and electromyography suggestive of myogenic and neurogenic damage;
3. muscle biopsy, showing muscle fibers of different sizes, atrophied muscle fibers in small round and small angular shapes, visible necrosis of muscle fibers, especially more muscle fibers are seen to appear rimmed with vacuoles, mononuclear cells are also seen to infiltrate the non-necrotic muscle fibers. Electron microscopy revealed tubulo-filamentous or myeloid inclusion bodies under the muscle membrane or in the nucleus.
Treatment
At present, there is no specific treatment, if the disease develops rapidly, and the pathology suggests that there are inflammatory cells infiltration, glucocorticoids and immunosuppressive therapy can be tried, but also can be used in large doses of immunoglobulin intravenous treatment, with a certain effect.