Inflammatory myositis

Question 1

What are the inflammatory myositis diseases?

Answer 1

disorders characterized by chronic, symmetrical proximal muscle weakness and inflammation. Often associated with elevated serum levels of skeletal muscle enzymes: CK, aldolase, ALT, AST, and LDH

Question 2

What are the true myositis diseases?

Answer 2

polymyositis and dermatomyositis

Question 3

epidemiology of myositis disease

Answer 3

bimodal age distribution: 10-15 yrs and 45-60. inclusion body and maligancy associated myositis more common after 50
women > men
highest levels in African Americans

Question 4

Risk factors of myositits

Answer 4

genetics, though we don’t know the genes; environmental (more in winter and spring)- maybe related to infectious agents like flu, coxsackie, picorna virus, echovirus. may also be related to foods, drugs, toxins, biologics, and medical devices

Question 5

general pathogenesis of myosititis

Answer 5

inflammation , degeneration, and necrosis of myofibrils; phagocytosis of necrotic cells and myofibril regeneration in polymyositis and inclusion body myosititis. destroyed fibers are replaced by fibrous CT and fat.
pro-inflammatory cytokines
incr. IL-1 and TNF-alpha in DM and PM
upregulation of MHC I molecs on myocytes

Question 6

clinical features of polymyositis: most common features

Answer 6

insidious onset w/o a precipitating event; bilateral, symmetric and proximal.
pelvic and shoulder girdle muscle involvement cardinal
may involve neck flexors, pharyngeal muscles (pneumonia risk), intercostals
see fatigue and post-exertional aches, cramps, and pains with objective muscle weakness

Question 7

polymyositits: what should I look for once I’ve made the dx?

Answer 7

arthralgia
interstitial lung disease
arrhythmias, CHF
esophageal disease/GERD
Renal: focal and mesangial proliferative glomerular nephritis

Question 8

Histology of polymyositis

Answer 8

focal inflammatory CD8+ T cells, plus macrophages that surroudn and invade initially non-necrotic fibers. inflammation in the muscle tissue.
T cells invade and destroy non-necrotic muscle fibers that express class I MHC molecs

Question 9

dermatomyositis: clinical features

Answer 9

features of polymyositis (insidious onset, bilateral, symmetric, and proximal, pelvic and shoulder girdle) PLUS cutaneous involvement like heliotropic rash, gottron’s papules, gottron’s sign, mechanics hands.
raynauds, periorbital edema, calcinosis more common in dermatomyositis

Question 10

What are Gottron’s papules/sign?

Answer 10

scaly red lesions over small joints. may be thickened.

Question 11

What is heliotropic rash? What other rashes are seen in dermatomyositis?

Answer 11

red face that does NOT spare the nasal/oral area; on the eyelids. Gottron’s papules, rash in shawl distribution, mechanic’s hands with dry palmar aspect and greasy type stains

Question 12

What are the peringual abnormalities of dermatomyositis?

Answer 12

abnormal, dilated vessels with loops and drop offs- highly suggestive of autoimmune disease

Question 13

histology of dermatomyositis

Answer 13

intramuscualr microangiopathy mediated by complement MAC. destruction of endothelial cells, loss of capillaries, muscle ischemia, muscle fiber necrosis.
inflammatory infiltrate is perivascular and composed of B and CD4+ lymphocytes
small vessel vasculopathy

Question 14

juvenile dermatomyositis

Answer 14

like adult disease but also has vasculitis, ectopic calcification, joint contractures, lipodystrophy; maybe hypertrichosis (too much hair)
more perifascicular atrophy
somewhat more severe picture

Question 15

Inclusion body myositis: clinical features and epi

Answer 15

may look very similar to polymyositis
weakness may be focal, distal, or asymmetric
mostly older ppl, more men
pts may have excess falling and difficulty making a fist
this is not an inflammatory myositis

Question 16

inclusion body myositis prognosis, histology, tests

Answer 16

normal or minimal CK elevation
slow and steady progression
may have neurogenic or mixed neurogenic/myopathic change
intracellular rimmed vacuoles that contain abnormal deposits of amyloid.

Question 17

approach to myositis associated with malignancy

Answer 17

controversial
don’t search extra, just do age appropriate screens
exception may be ovarian CA, which may be over represented

Question 18

amyopathic dermatomyositis

Answer 18

biopsy confirmed classic cutaneous findings of DM but no clinical evidence of muscle disease. fatigue may be prominent complaint

Question 19

antisynthetases

Answer 19

myositis antibody that is seen in 1/3 pts with polymyositis or dermatomyositis
cause acute onset with constitutional symptoms
often have interstitial lung disease, arthritis, Raynaud’s mechanic’s hands. immuniprecipitation of tRNA to inhibit enzyme function. esp. Anti-Jo-1 ab in pm (more than DM)

Question 20

anti-signal recognition particle antibodies

Answer 20

uncommon
get PM of rapid onset and are relatively treatment resistant
may develop cardiomyopathy and distal muscle weakness

Question 21

anti-Mi-2

Answer 21

very rare, seen in younger pts, suggests good response to therapy. seen in dermatomyositits

Question 22

myositis diagnosis modalities/tools

Answer 22

blood tests (CK)
anemia of chronic disease
emg can help
mri can show areas of inflammation and guide biopsy location
muscle biopsy needed to confirm dx

Question 23

tx of myositis

Answer 23

glucocorticoids as first line. 50-75% get remission- and the earlier you start, the better
then, try methotrexate (or, second line azathioprine, or even stronger antimetabolites. hydroxychloroquine for the skin)
other options: IVIG, plasmapharesis, PE, rituxiumab for dermatomyositits