Idiopathic inflammatory myopathy
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- 1. Inflammatory myopathies are rare diseases. Incidence range from 2.27.7 cases per million. Age at onset has a bimodal distribution with peaks observed between ages 10 and 15 years in children and between 45 and 60 years in adults.
2. Women are affected twice as commonly as men, with the exception of inclusion body myositis, in which men are affected more often. 3. Clinical Classification of the IdiopathicInflammatory MyopathiesPolymyositisDermatomyositisJuvenile dermatomyositisMyositis associated with neoplasiaMyositis associated with connective tissue diseaseInclusion body myositis 4. CRITERIA muscle weakness1. Symmetric proximal2. Muscle biopsy evidence of myositis3. Increase in serum skeletal muscle enzymes4. Characteristic electromyographic pattern5. Typical rash dermatomyositis 5. Presentation 6. Clinical Features Proximal and symmetric muscle weakness is thecardinal clinical feature of the inflammatorymyopathies. Weakness of the proximal muscles of the legs isusually noted first and results in difficulty arising froma chair or climbing stairs. Weakness of the proximal arm muscles may limit theability to lift heavy items, to brush ones hair, or toreach up to shelves. 7. The detection of muscle weakness on physicalexamination typically relies on manual musclestrength testing and is usually rated on a scale of 0 to5. Functional measurements of muscle strength are oftenhelpful. These include determining how long it takes thepatient to arise ten times from a chair without use ofthe arms or to walk 10 meters. The patients ability torise from a squat or stand on his or her toes and heelscan also be assessed 8. Pelvic and shoulder girdle musculature are affectedmost, but weakness of neck muscles, particularly theflexors, is also common. Ocular and facial muscles are virtually never involved. Dysphagia may develop secondary to esophagealdysfunction or cricopharyngeal obstruction. 9. Pharyngeal muscle weakness may cause dysphonia anddifficulty swallowing. Pulmonary and cardiac manifestations may precedethe onset of muscle weakness or develop at any timeduring the course of disease. 10. The clinical features of dermatomyositis include all thosedescribed for polymyositis plus a variety of cutaneousmanifestations. Two cutaneous manifestations are consideredpathognomonic.1. Gottron papules (symmetric lacy pink or violaceous raised lesions typically found on the dorsal and lateral aspects of the interphalangeal and metacarpophalangeal joints)2. Gottron sign (symmetric macular violaceous erythema overlying the dorsal aspects of the interphalangeal and metacarpophalangeal joints, olecranon processes, patellae, and medial malleoli) 11. Gottron papules 12. Gottron sign 13. Characteristic cutaneous findings :1. Heliotrope (violaceous) discoloration of the eyelids.2. Macular erythema of the posterior shoulders and neck (shawl sign).3. Anterior neck and upper chest (V sign).4. Dystrophic cuticles; and5. Periungual telangiectases and nailfold capillary changes. 14. Heliotrope rash of dermatomyositis demonstrating both erythemaand diffuse periorbital edema. 15. Heliotrope rash 16. V-neck rash in a patient with dermatomyositis demonstratingphotosensitive nature over anterior chest. 17. Shawl sign in a patient with dermatomyositis featuring anerythematous rash across the upper back and extending onto the neckin thedistribution of where a shawl is worn. 18. Cuticular overgrowth with periungual erythema and capillarydilatation in a patient with dermatomyositis. 19. "Mechanics hands" refers to darkened or dirty-appearing horizontal lines and fissures that are seenacross the lateral and palmar aspects of the fingers. This skin lesion can be seen in both dermatomyositisand the anti-synthetase syndrome subset ofpolymyositis. 20. Mechanics hands. Note the erythema and hyperkeratotic changesand cracking of the skin on the lateral aspects of the fingers in thispatient with the anti-Jo-1 autoantibody. 21. Juvenile dermatomyositis 22. In juvenile dermatomyositis, the skin lesions andweakness are almost always coincidental, but theseverity and progression of each varies greatly frompatient to patient. Juvenile variant differs from the adult form because ofthe coexistence of vasculitis, ectopic calcification, andlipodystrophy. 23. Vasculitic ulcers 24. Gastrointestinal ulcerations resulting from vasculitiscan cause hemorrhage or perforation of a viscus. Ectopic calcification may occur in the subcutaneoustissues or in the muscles. 25. Amyopathic dermatomyositis : Biopsy-confirmed,classic cutaneous findings of dermatomyositis havenormal muscle strength, muscle enzymes,electromyograms (EMGs). Dermatomyositis sine myositis: Above findings plusnormal muscle histology 26. Muscle weakness associated with an underlyingmalignancy develops in a subset of patients withinflammatory myopathies. Malignancy may precede, or develop after, the onset ofmuscle weakness, usually the two are diagnosed within a 1-year period. The sites or types of malignancy that occur in associationwith myositis are those that are expected for the age andgender of the patient. 27. Inclusion body myositis mainly affects persons overthe age of 50 years . It affects men twice as often as women. Symptoms are often present for 58 years before thediagnosis is made. Predominant weakness of the quadriceps, long fingerflexors, and anterior calf muscles is characteristic. 28. Laboratory Findings An abnormal creatine kinase (CK) level is possibly themost sensitive indicator of skeletal muscle damage. Normal levels of CK may be found1. Very early in the course of polymyositis.2. Dermatomyositis.3. In advanced cases with significant muscle atrophy.4. In myositis associated with a malignancy.5. Inclusion body myositis. 29. Tests of acute phase reactants, the erythrocytesedimentation rate and C-reactive protein levels, areabnormal in only some patients with myositis. The erythrocyte sedimentation rate is normal in abouthalf of patients with polymyositis and is elevatedabove 50 mm/h (Westergren method) in only 20%. 30. Certain autoantibodies are found almost exclusively inpatients with idiopathic inflammatory myopathies,and therefore are termed myositis-specificautoantibodies . Antinuclear antibodies (ANAs) may be found in theserum of over 50% of patients with inflammatorymuscle disease 31. Most myositis-specific autoantibodies are directedagainst amino acyl-tRNA synthetase activities. The most common of these is anti-histidyl-tRNAsynthetase (Jo-1), present in approximately 20% ofpatients with polymyositis 32. Patients with these autoantibodies typically manifestmyositis (polymyositis more commonly thandermatomyositis) plus several extramuscular featuresincluding interstitial lung disease, arthritis,mechanics hands, and Raynaud phenomenon. The combination of these features and aninflammatory myopathy has been termed"antisynthetase syndrome." 33. EMG EMG is quite effective for :1. Differentiating between myopathic and neuropathicconditions.2. Localizing a neurologic lesion to the central nervoussystem, spinal cord anterior horn cell, peripheral nerves,or neuromuscular junction.3. In addition, knowledge of the distribution and severityof abnormalities can guide selection of the mostappropriate site to biopsy if MRI is not available. 34. In polymyositis and dermatomyositis, EMG classically reveals the following triad:1.Increased insertional activity, fibrillations, and positive sharp waves.2. Spontaneous, bizarre high-frequency discharges.3. Polyphasic motor unit potentials of low amplitude and short duration. 35. Muscle histology In classic polymyositis, muscle biopsies reflect a T-cellmediated autoimmune process. The lymphocytic cell infiltrate is found predominantlyin endomysial locations. T lymphocytes, especially CD8+ cytotoxic T cells, canbe seen surrounding and invading non-necrotic fibersexpressing class I major histocompatibility antigen. 36. The muscle biopsy in inclusion body myositis closelyresembles that of polymyositis, with endomysialinflammatory infiltrates and CD8+ T-cell invasion of non-necrotic muscle fibers. However, a characteristic feature of inclusion body myositisis the presence of intracellular vacuoles. The vacuoles contain basophilic (red on Gomori trichromestain) granules in their center or along their walls, leadingto their "red-rimmed" appearance. 37. Treatment Glucocorticoids are the standard first-line medicationfor any idiopathic inflammatory myopathy. Initially, prednisone is usually given in a single dose of1 mg/kg/d, but in severe cases, the daily dose can bedivided or intravenous methylprednisolone can beused. 38. If a patient does not respond to glucocorticoid therapy,another agent is added, usually either azathioprine ormethotrexate. Intravenous immune globulin is often beneficial in thetreatment of dermatomyositis and polymyositis, butits effect is short-lived and repeat infusions aregenerally necessary every 68 weeks. 39. Other immunosuppressive agents or therapeutic modalities have been used in treatment-resistant patients, including1) Cyclophosphamide,2) Cyclosporine3) Tacrolimus4) Rituximab5) Etanercept6) Infliximab7)Mycophenolate mofetil8)Plasmapheresis9) Total-body (or total-nodal) irradiation.