Inflammatory myopathies

Question 1

Classification of inflammatory myopathies

Answer 1

• Idiopathic inflammatory myopathies (most of them): polymyositis (almost exclusively adults), dermatomyositis (both adults and children), inclusion body myositis, myositis associated w/ malignancy
• Peak incidence is 40-50, all have higher incidence in women except inclusion body myopathies (3:1 male:female)
• Infectious myopathies
• Drug and toxin induced myopathies
• Metabolic, endocrine, hereditary

Question 2

Dx and testing for myopathies

Answer 2

• Dx based on 5 Sx: proximal muscle weakness, elevated muscle nz (CK, aldolase, ALT, AST, LDH), myopathic EMG, muscle biopsy w/o inflammation, skin rash if dermatomyositis (DM)
• Testing includes PE (strength assessment; 3 is gravity only), labs (CK, aldolase, AST, ALT, LDH)
• Myoglobinuria is not seen in myopathies, but is seen in rhabdomyolitis
• Use MRI for imaging purposes

Question 3

Polymyositis (PM)

Answer 3

• Insidious onset over several months, usually systemic Sx
• Weakness of shoulder and pelvis and neck muscles (50% w/ pain/tenderness)
• Occasional involvement of pharyngeal muscles
• Pulmonary involvement: interstitial fibrosis
• There can be antisynthetase syndrome (anti-Jo1 Abs) associated w/ it, Sx include interstitial lung disease, fever, mechanic’s hands (thickened cracked hands), raynauds phenomenon
• CD8 cells to endomysium

Question 4

Biopsy results for myopathies

Answer 4

• PM: inflammation of the endomysium by CD8 cells (w/ fibrosis)
• DM: perivascular B cells and CD4 cells, fiber atrophy @ margins of fascicles (perimysium)
• Inclusion body myositis (IBM): similar to PM, w/ “ragged red” fibers, inclusion bodies

Question 5

Dermatomyositis (DM)

Answer 5

• PM clinical findings plus cutaneous changes, perivascular CD4 and B cells to perimysial blood vessels
• Gottrons papules: erythematous lesion over knuckles and elbows
• Discoloration of eyelids
• Shawl sign (rash on back of neck)
• V sign (rash on chest)
• There can be antisynthetase syndrome (anti-Jo1 Abs) associated w/ it, Sx include interstitial lung disease, fever, mechanic’s hands (thickened cracked hands), raynauds phenomenon

Question 6

Juvenile dermatomyositis

Answer 6

• Similar to adult DM but w/ vasculitis, calcification and lipodystrophy
• Often autoAbs involved
• There can be antisynthetase syndrome (anti-Jo1 Abs) associated w/ it, Sx include interstitial lung disease, fever, mechanic’s hands (thickened cracked hands), raynauds phenomenon

Question 7

Inclusion body myositis (IBM)

Answer 7

• Up to 1/4 of inflammatory myopathies, rare if pt is under 40
• Inclusion bodies of neurodegenerative proteins
• Poor response to Rx, slower onset
• Can affect proximal and distal muscles and can be asymmetric
• Mildly elevated CPK

Question 8

Rx of inflammatory myopathies

Answer 8

• Corticosteroids are 1st line
• Goal is normalization of muscle nzs and increased strength
• PT is a must
• Better outcomes w/ early Rx
• Pharyngial/lung involvement has poor outcomes, as does IBM