• Inflammatory myopathies:
o Dermatomyositis DM
o Polymyositis PM
o Immune-mediated necrotizing myopathy IMNM
o Anti synthetase syndrome ASS
o Myositis with inclusion bodies IBM
Laboratory Findings
• Muscle enzymes
o The most sensitive muscle enzyme is creatinine kinase (CK), which often parallels disease activity
o Sometimes in DM, aldolase can be found to be high while CK is normal.
• EMG
o Myopathic findings reflecting muscle damage are detected.
• Muscle biopsy
o It is the most sensitive and specific diagnostic method.
o Perimiscial inflammation and perifascicular atrophy (pathognomonic) are seen in dermatomyositis.
o In polymyositis, endomysial inflammation is seen.
o Biopsy findings of inclusion body myositis are similar to PM. In addition, Congo red positive (amyloid-containing) vacuoles are seen.
specific diseases
• Dermatomyositis (DM);
o Muscle weakness shows a subacute (weeks to months) course.
o Proximal muscles (especially hip and shoulder muscles) are predominantly involved.
o Therefore; There is difficulty in getting up from a chair, climbing stairs, combing hair, etc.
o Characteristic skin findings distinguish DM from other myositis.
o Skin manifestations;
Heliotrop rash (blue-purple spot and edema around the eyelid) Pathognomonic
Gottron papules (Pink-purple plaques on the dorsal side of the hand) Pathognomonic
V sign (erythema spreading from the front of the neck to the chest)
Shawl sign (erythema spreading from the neck to the back of the shoulder)
o DM can be seen as paraneoplastic, especially in adult patients.
o Myositis-specific antibodies;
Anti-MDAS: Associated with amyopathic DM (no muscle involvement; severe palmar rash, finger ulcers, and rapidly progressive interstitial lung disease).
Anti-Mi2: Associated with very good treatment response and good prognosis.
• Polymyositis (PM);
o It is similar to DM in terms of muscle involvement (bilateral, symmetrical, proximal) and course (week-month).
o It may be associated with malignancy such as DM (paraneoplastic).
DM and PM other muscle involvement
Pharynx-larynx muscles (dysarthria-dysphonia), upper esophageal muscles (dysphagia) and heart muscles may also be involved.
Dyspnea may occur due to respiratory muscle involvement or interstitial lung disease.
Ocular and mimic muscles are not expected to be involved.
• Inclusion body myositis (IBM);
o Patients are usually over 50 years old and mostly male.
o Muscle weakness progresses slowly (over years).
o Unlike other myositis, the muscles are kept asymmetrically (not proximal muscle).
o CK levels may be normal or slightly increased (< 10 times).
o IBM-associated autoantibody is anti-cNlA antibody.
Treatment
• It is usually started with oral steroid therapy.
• If muscle weakness develops under steroid therapy, there are 2 possible situations:
o Steroid myopathy (low CK, muscle weakness associated with high steroid dose)
o Myositis relapse (high CK, muscle weakness associated with low steroid dose)
• Immunosuppressives such as methotrexate, azathioprine, mycophenolate mofetil, etc. can be used in second-line treatment.