Idiopathic Inflammatory Myopathy (Investigation (ACR Diagnostic Criteria (…
Idiopathic Inflammatory Myopathy
An inflammatory process of unknown etiology affecting predominantly the muscles, though it can also involve the skin and internal organs.
1.Polymyositis (PM) 2.Dermatomyositis (DM)
3.Inclusion Body Myositis (IBM) 4.Juvenile Dermatomyositis (JDM)
5.Myositis associated with malignancy (paraneoplastic syndrome)
6.Myositis associated with other connective tissue disorders
in all races
in all ages (bi-modal distribution of onset: childhood, around the age of 40)
women – three times more
unknown, viruses (Coxsackie, rubella, influenza), HLA-B8/DR3
Signs and Symptoms
proximal muscle weakness:
involvement of pharyngeal, laryngeal and respiratory muscle can lead to dysphagia, dysphonia and respiratory failure,
possibly leading to aspiration pneumonia.
muscle pain and tenderness.
arthritis and arthralgia
Raynaud's phenomenon is common
Fatigue, Low-grade fevers
Morning stiffness, Weight loss
dysrhythmias, heart failure, ventricular hypertrophy, pericarditis.
CK-MB often elevated, but is produced by regenerating skeletal muscle
Jo-1 antibody is most common anti-synthetase Ab.
Interstitial lung disease, Mechanic’s hands
skin eruption (heliotrop rash, periorbital oedema, Gotron’s papules, Gottron’s sign, V sign, mechanic’s hands, shawl sign: erythematous rash over neck), polyarthritis.
DM is associated with cancer ~32%, PM ~15%.
Most common CA: ovarian, lung, breast, GI, NHL.
commonly affect the children between the age of 4 -10 years.
Muscle weakness is usually associated with typical rash of dermatositis.
differs from adult form because of co-existence of vasculitis and ectopic calcification.
Inclusion body myositis
usually in men over 50 years.
Weakness of the pharyngeal muscles causes difficulty in swallowing in over 50%.
slowly progressive weakness of mainly distal muscles.
Creatine kinase is only slightly elevated
EMG shows both myopathic and neuropathic changes
MRI, the changes are often more distal but can be similar to polymyositis.
A muscle biopsy shows inflammation and basophilic rimmed vacuoles with diagnostic filamentous inclusions and vacuoles on electro microscopy.
ACR Diagnostic Criteria
Symmetrical weakness – Limb-girdle and neck flexors, with or without dysphagia/respiratory problems
Elevation of muscle enzymes in serum – CK, aldolase, LDH, AST, ALT
Dermatologic features – Gottron’s sign, heliotrope rash, shawl sign, photosensitivity.
Definite 4 criteria, no rash
Probable 3 criteria, no rash
Possible 2 criteria, no rash
Definite Rash + 3 criteria
Probable Rash + 2 criteria
Possible Rash + 1 criteria
The diagnosis of polymyositis is made on the basis of 3 tests, 2 of which at least should be positive
1.Muscle enzyme: serum creatinine phosphokinase (CPK) and aldolase are raised , ALT , AST , LDH.
2.Electromyography (EMG) : show tried of changes of myositis :
A- spontaneous fibrillation potential at rest
B- polyphasic or short duration potential on voluntary contraction
C- salvos of repetitive potential on mechanical stimulation of the nerves .
necrosis and fibrosis of muscle fiber
swelling and disruption of muscle cells
inflammatory cell within muscle fascicule in polymyositis
and surrounding muscle fascicule in dermatomyositis
Myositis-specific Ab’s (30-40% sensitivity):
– Anti-synthetase: Jo-1, Anti-PL7 (threonyl-tRNA synthetase), Anti-PL-12 antibodies (anti- alanyl-tRNA synthetase)
– Non-synthetase antibodies: Mi2, Anti-SRP (Anti-signal recognition particle)
high-dose corticosteroids is the initial treatment of choice for the inflammatory myopathies
Second-line therapies vary, almost every immunomodulator has been used:
– MTX – CsA – Azathioprine – MMF – Infliximab,etanercept,rituximab – IVIg – Plasma exchange
Failure to respond to therapy may suggest:
-Inclusion body myositis
-Steroid-resistance or steroid-induced myopathy
May also indicate:
-Inadequate dose of prednisone or early taper
-Early discontinuation of prednisone without keeping a maintenance low dose therpay
• PM is CD8 cell-mediated muscle necrosis, found in adults
• DMM is Β-cell and CD4 immune complex-mediated peri-fascicular vascular abnormalities