Term
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Definition
Idiopathic Inflammatory Myopathy (IIM):
-Polymyositsis
- Dermatomysitis
-Juvenile dermatomyositis
Malignancy associated myositis
Inclusion body myositis (IBM)
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Term
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Definition
0.5 - 8.4 cases /million (rare)
Peak age at onset:
in children- 10-15 yrs
in adults- 45 and 60 yrs
Malignancy associated myositis-age > 50 yrs
Inclusion body myositis- age > 50 yrs
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Term
IIM: Genetics and Epidemiology |
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Definition
IIM
Men:Women = 1:2
Highest incidence in Blacks
Lowest incidence in Japanese
Inclusion body myositis
Men:Women = 2:1
HLA-DR3 is associated with an increased risk of the development of PM and Juvenile DM.
High prevalence of HLA-138, HLA-DR3, and DR6 in caucasian patients.
Anti-synthetase antibody syndrome (a subset of IIM) is associated with the presence of HLA DR-52.
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Term
Diagnostic Criteria for PM/DM |
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Definition
Peter/Bohan criteria
1. Symmetric proximal muscle weakness
2. Elevated serum muscle enzymes
3. Myopathic changes on EMG
4. Characteristic muscle biopsy abnormalities
5. Typical rash of dermatomyositis ( for DM )
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Term
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Definition
IIMs are immune-mediated processes, believed to be triggered by environmental factors in genetically susceptible individuals.
The specific causes or triggering events of IIM remain unknown, but viruses have been strongly implicated.
Autoantibodies may be present but are of unknown pathogenic significance.
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Term
Approach to the diagnosis of PM/DM
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Definition
1. A patient with a compatible history and proximal weakness initially be evaluated by measuring muscle enzymes.
2.If the muscle enzymes are elevated, an objective evaluation of muscle inflammation is performed (unilateral EMG or bilateral thigh MRI) to document muscle abnormality and to identify a site for biopsy (the muscle biopsy is a definitive test to establish the diagnosis).
3. Once that site is identified, a biopsy is performed (prior to treatment) to document the presence of active myositis.
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Term
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Definition
The biopsy should be obtained from a weak or objectively inflamed muscle as identified by the EMG or MRI,usually quadriceps or deltoid.
Avoid muscle with atrophy,especially chronic.
Open biopsy is preferred to a close needle biopsy.
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Term
Common histologic features of PM/DM
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Definition
Muscle fiber necrosis
Muscle fiber degeneration
Muscle fiber regeneration
Inflammatory cell infiltrate (lymphocytic)
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Term
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Definition
Cell-mediated disorder
Cellular infiltrate is predominantly within the fascicle with inflammatory cells invading individual muscle fibers. There are increased numbers of cytotoxic CD8+ T cells.
No signs of vasculopathy.
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Term
Dermatomyositis Pathology |
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Definition
Humorally-mediated disorder.
Primary lesion is vasculitis within/around the muscle.
Predominantly perifascicular and often perivascular inflammatory infiltrate, mostly composed of B lymphocytes and an increased ratio of CD4/CD8
T cells.
Perifascicular atrophy and fibrosis
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Term
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Definition
Onset of symptoms usually occurs over 3-6 months
Symmetric proximal muscle weakness
(shoulder, pelvic girdle, neck muscles, and upper 1/3 of esophagus)
Dysphagia, aspiration and reflux
Dysphonia
Ocular and facial muscles are spared
Pain and tenderness are mild (if present at all) and occurs in only 25-50% of patients
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Term
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Definition
Fever
Weight loss
Non-erosive inflammatory polyarthritis
Raynaud’s phenomenon
Myocarditis with asymptomatic ECG changes or
SVT resulting in CHF
Aspiration pneumonia
Interstitial lung disease associated with anti- synthetase antibodies
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Term
Rashes in Dermatomyositis |
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Definition
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Gottron’s papules
Most common and considered pathognomonic.
Symmetric scaly, erythematous eruption over the extensor surfaces of MCP, IP joints, elbows , knees and medial malleoli.
Heliotrope rash
Reddish-violaceous eruption on the upper eyelids, often accompanied by swelling of the eyelid.
Most specific.
Seen in a minority of patients.
Biopsy reveals vascular ectasia alternating with areas of vascular dropout.
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Term
Other cutaneous manifestations of DM |
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Definition
Abnormal nail bed capillary loops
Calcinosis cutis rarely
Diffuse flat erythema over forehead, malar region involving nasolabial folds, chin.
Dystrophic cuticles
“Mechanic’s hands”
Panniculitis
Periungual erythema
Photosensitivity
Shawl sign
V-sign
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Term
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Definition
Elevated muscle-associated enzymes
( CPK, AST, ALT, LDH, Aldolase )
CPK level usually correlates with severity of muscle inflammation but can be normal.
Serial muscle enzyme measurements are useful in following myositis activity (however do not replace serial strength testing).
If CPK is normal (due to circulating inhibitors) the other muscle enzymes may be abnormal.
Elevated levels of CPK or AST,ALT,LDH may cause confusion with an underlying diagnosis of MI or hepatitis.
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Term
Other Laboratory Findings |
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Definition
Heme + urine without RBCs indicates myoglobinuria which may be nephrotoxic.
Leukocytosis and thrombocytosis may occur in some patients.
Elevated ESR and/or CRP occurs in <50% of patients, therefore is not useful.
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Term
Myositis specific antibodies
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Definition
Are directed against cytoplasmic RNA synthetases, other cytoplasmic proteins and nuclear antigens.
They serve as markers for a discrete subgroup of patients with characteristic clinical manifestations and prognosis.
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Term
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Definition
Classic Triad, seen in only 40% of patients
1.Increased insertional activity, fibrillations and sharp positive waves.
2.Spontaneous, bizarre, high frequency discharges.
3.Polyphasic motor unit potentials of low amplitude and short duration.
EMG findings distinguish myopathic from neuropathic disorders and assists in identifying the site for a muscle biopsy.
Unilateral EMG is crucial to avoid biopsy of muscle with electrical burn artifact.
10-15% of patients with IIM have a normal EMG
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Term
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Definition
MRI
Identifies areas of muscle edema (interpreted as inflammation) in muscles with active myositis.
Also identifies muscle fibrosis and calcification.
Noninvasive, can assess large areas of muscle and can avoid problems with sampling error.
Can be repeated serially to assess the course and response to therapy.
Potentially an alternative to EMG.
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Term
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Definition
0.2/100K
F:M 5:1
Juvenile DM occurs 10-20 times more often than Juvenile PM
More prominent vasculitis with GI ulceration, bleeding, perforation.
Ectopic calcification
Lipodystrophy
Skin lesions and weakness are almost always coincidental.
Histology similar to adult form although perifascicular atrophy is much more prevalent.
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Term
Inclusion Body Myositis (IBM) |
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Definition
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Male, usually >50 years old.
Associated with HLA DR1, DR6, and DQ1.
Symptoms begin insidiously and progress slowly. Symptoms are often present for 5-6 years before diagnosis.
May be focal, distal, asymmetric weakness.
Neurogenic and myopathic changes on EMG.
Dysphagia, atrophy, diminished tendon reflexes.
Resistant to conventional therapy.
On muscle biopsy:
Intracellular vacuoles lined with basophilic granules on frozen sections.
Electron microscopy reveals tubular or filamentous intracytoplasmic or intranuclear inclusions (or inclusion bodies).
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Term
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Definition
Supportive Treatment:
Avoidance of sunlight/use of sunscreens in DM Physical therapy
Aspiration precautions
Prevention of Osteoporosis
Medications:
Prednisone 1 mg/kg/day (IBM is resistant)
Methotrexate
Azathioprine
IV IgG.
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Term
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Definition
80-90% - 15 yr survival
Higher Morbidity and Mortality in black females especially when the age at onset > 45 years.
There may be an increased prevalence of neoplasia in patients with PM and DM at older age onset (malignancy associated myositis).
Therefore adults > 50 years old with new onset IIM should be screened for an underlying malignancy.
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