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Toronto Notes 2019 Connective Tissue Disorders Idiopathic Inflammatory Myopathy
Definition
• autoimmunediseasescharacterizedbyproximalmuscleweakness±pain
• musclebecomesdamagedbyanon-suppurativelymphocyticinflammatoryprocess • associatedwithmalignancy
■ increased risk of malignancy: age >50, DMM>PM, normal CK, refractory disease
• associatedwithotherconnectivetissuedisease,Raynaud’sphenomenon,autoimmunedisorders
Classification
• PM/DMM
• adultandjuvenileform
Inclusion Body Myositis
• age>50,M>F,slowlyprogressive,vacuolesincellsonbiopsy • suspectwhenpatientunresponsivetotreatment
• distalaswellasproximalmuscleweakness
• musclebiopsypositiveforinclusionbodies
POLYMYOSITIS/DERMATOMYOSITIS
Table 19. Classification Criteria for PM/DMM*
Rheumatology RH15
Criteria
1. Symmetric proximal muscle weakness 2. Elevated muscle enzymes
3. EMG changes
4. Muscle biopsy
Description
Typical involvement of shoulder girdle and hip girdle
CK, aldolase, LDH, AST, ALT
Short polyphasic motor units, high frequency repetitive discharge, insertional irritability
Segmental fibre necrosis, basophilic regeneration, perivascular inflammation (DMM), endomysial inflammation (PM) and atrophy
5. Typical rash of dermatomyositis *Definite if 4 present, probable if 3 present
Required for diagnosis of DMM (see below) NEJM 1975;292:403-407
Etiology and Pathophysiology
• PMisCD8cell-mediatedmusclenecrosis,foundinadults
• DMMisΒ-cellandCD4immunecomplex-mediated,andcausesperi-fascicularvascularabnormalities
Signs and Symptoms
• progressivesymmetricalproximalmuscleweakness(shoulderandhip)developingoverweeksto months
■ difficulty lifting head off pillow, arising from chair, climbing stairs
• dermatological
■ DMM has characteristic dermatological features (F>M, children and adults) ◆ Gottron’s papules
– pink-violaceous, flat-topped papules overlying the dorsal surface of the interphalangeal joints
◆ Gottron’s sign
– erythematous, smooth or scaly patches over the dorsal IPs, MCPs, elbows, knees, or medial
malleoli
◆ heliotrope rash: violaceous rash over the eyelids; usually with edema
◆ shawl sign: poikilodermatous erythematous rash over neck, upper chest, and shoulders
◆ mechanic’s hands: dry, crackled lesions on palmar and lateral surface of digits, especially over the
pulp space
◆ periungual erythema
• cardiac
■ arrhythmias, CHF, conduction defect, ventricular hypertrophy, pericarditis
• gastrointestinal
■ oropharyngeal and lower esophageal dysphagia, reflux
• pulmonary
■ weakness of respiratory muscles, ILD, aspiration pneumonia
Investigations
• bloodwork:CK,ANA,anti-Jo-1(DMM),anti-Mi-2,anti-SRP
• imaging:MRImaybeusedtolocalizebiopsysite
• EMG:characteristicfindingsofmuscleinflammationanddamage
■ muscle biopsy can aid in diagnosis, however not needed in those with classic skin findings and muscle weakness
Signs of DMM
Gottron’s papules and Gottron’s sign are pathognomonic of DMM (occur in 70% of patients)
Malignancies Associated with DMM
• Breast • Lung
• Colon • Ovarian