Inflammatory Myositis Flashcards
What is the epidemiology of idiopathic inflammatory myositis?
- Female to male ratio: 2:1
- DM bimodal distribution of onset, highest in 2nd and 4th decade
- PM peaks in 4th decade
- IBM typically affects men >50yo
What is the pathophysiology of DM/PM/IBM (muscle biopsy findings)
- DM is typically associated with a mixed B and CD4- positive T-cell perivascular infiltrate, vasculitis with microinfarction and grouping of muscle fibers, and perifascicular muscle atrophy.
- PM infiltrates primarily consist of CD8- positive T cells, involving all layers of muscle fibers with invasion and myophagocytosis.
- The primary target seems to be the vascular endothelium in DM and the myofibrils themselves in PM.
- IBM demonstrates a mild T-cell predominant inflammatory infiltrate (similar to PM), along with the presence of rimmed vacuoles and eosinophilic and basophilic inclusions within muscle fibers. Filamentous tubules seen on electron microscopy are highly specific for IBM.
Characterisitics of anti-synthetase syndrome
Anti-jo positive plus 2 of the following features
- Raynauds
- Mechanics hands
- ILD
- Non erosive inflammatory arthritis
Features of DM vs PM vs IBM
Epidemiology
- DM: bimodal, 2nd + 4th decade, female > male, no familial association
- PM: female > male, <50yo, no familial association
- IBM: male > female, >50yo, familial association
Clinical Presentation
- DM + PM: acute + subacute onset, proximal weakness (deltoids, arm/hip flexors, neck flexors), rapid course. Have systemic features (fever, fatigue, weight loss)
- DM has skin features: helioptrope rash, gottrons papules, shawl sign
- IBM: insidious onset, proximal + distal weakness (difficulty gripping objects), slowly progressive course, nil skin rash. Rarely associated with extra-muscular manifestations.
Diagnostic Findings
- DM + PM: CK >10 times normal, myopathic on EMG
- IBM: CK <10 times noormal, myoneuropathic on EMG
Muscle Biopsy
- DM: microinfarctions, myofibril grouping
- PM: myofibril necrosis
- IBM: rimmed vacuoles, inclusions
Tx
- DM+ PM: good response
- IBM: poor response
What weakness is involved in PM and DM
Proximal weakness especially affecting the deltoids, arm/hip flexors, neck flexors - classic triad of hair/chair/stair - difficulty combing hair, rising from chair and climbing stairs.
What weakness is involved in IBM?
- Proximal and distal weakness
- Normally symmetrical but can be asymmetrical
- Onset insidious and slowly progressive
Cutaneous manifestations of DM
DM is associated with multiple cutaneous manifestations.
- Gottron sign/papules are symmetric erythematous/violaceous macules, patches, or papules located on the extensor surfaces of the metacarpophalangeal joints
- Common rashes include heliotrope rash (edematous lilac discoloration of periorbital tissue) as well as photodistributed rashes such as the shawl sign (upper back) and V sign (neck/upper chest)
- Poikiloderma (mottled pigmentation, epidermal atrophy, and telangiectasia) can occur in both sun-exposed and unexposed areas.
- Gottron sign/papules and heliotrope rash are considered pathognomonic for DM.
- Nail changes such as cuticular hypertrophy or nailfold capillary abnormalities can occur.
- Amyopathic DM refers to classic cutaneous findings occurring in the absence of muscle involvement.
- Mechanic’s hands, characterized by hyperkeratotic fissuring of the palmar and lateral surfaces of the fingers , is seen in both DM and PM
- The skin is generally uninvolved in PM and IBM
Cardiopulmonary and gastrointestinal involvement in IIM.
Cardiopulmonary:
- All of the IIMs can cause chest wall and diaphragm muscle weakness, resulting in shortness of breath and occasionally respiratory failure
- ILD in PM/DM
- Myocarditis, AV block, heart failure in PM/DM
GIT:
- Weakness of the striated muscle of the upper esophagus or oropharynx is common in IIM and can lead lo dysphagia, aspiration, regurgitation. and associated pneumonitis.
Esophageal disease is more common among older patients and those with inclusion body myositis.
ILD in IIM.
ILD is commonly in DM and PM and may precede muscle symptoms.
Often associated with antisynthetase syndrome (anti-jo1) and is associated with poor prognosis.
In which IIM is there a risk of malignancy?
Both DM and PM increases the risk of malignancy, especially DM!
- Breast/pelvic/prostate exam
- Mammography
- Colonoscopy
Cancers associated with DM and PM are similar to those seen in the general population. including adenocarcinomas of the bladder, cervix, lung, ovaries, pancreas, and stomach.
Ovarian cancer risk may be especially increased.
Does the degree of CK rise correlate to disease in DM/PM?
In DM and PM, muscle enzyme elevation is dramatic (usually 10- to 50-fold the upper limit of normal) but may or may not correlate with degree of weakness.
What is amyopathic DM?
Amyopathic DM refers to DM with cutaneous involvement and normal muscle enzyme levels in the absence of muscle manifestations.
What is mixed connective tissue disease?
Usually combination of SLE and cleroderma
Anti-RNP
EMG findings of IIM
The characteristic triad of EMG findings includes short duration small, low-amplitude polyphasic potentials; fibrillation potentials at rest; and bizarre, high frequency, repetitive discharges
What is the gold standard ix for IIM?
Muscle biopsy
• DM: CD4 T cells, microinfarctions, myofibril grouping
Is typically associated with a mixed B and CD4- positive T-cell perivascular infiltrate, vasculitis with microinfarction and grouping of muscle fibers, and perifascicular muscle atrophy.
• PM: CD8 T cells, myofibril necrosis
Infiltrates primarily consist of CD8- positive T cells, involving all layers of muscle fibers with invasion and myophagocytosis.
• The primary target seems to be the vascular endothelium in DM and the myofibrils themselves in PM.
• IBM: rimmed vacuoles, influsions
Demonstrates a mild T-cell predominant inflammatory infiltrate (similar to PM), along with the presence of rimmed vacuoles and eosinophilic and basophilic inclusions within muscle fibers. Filamentous tubules seen on electron microscopy are highly specific for IBM.
