myopathies

Question 1

what is inclusion body myositis?

Answer 1

it is an inflammatory insidious degenerative myopathy leading to muscle weakness over years

it is unusual for myositis - it causes a distal upper limb weakness (but proximal lower limb)

cK is usually elevated, but usually less than 2000, often less than 1000

there seems to be an accumulation of amyloid protein in rimmed vacuoles, and later a T cell response leading to inflammation

limited treatment options

Question 2

what are the typical skin findings of patients with dermatomyositis?

Answer 2

Gottron’s papules and heliotrope rash over the face (a violaceous rash)

Question 3

what is the clinical presentation of dermatomyositis and polymyositis

Answer 3

slow onset proximal muscle weakness

can have cutaneous signs
Raynaud's 
cK elevation
elevated AST/LDH from muscle
can have associated ILD (and associated signs/Sx)

Question 4

what is the difference pathogeically between polymyositis and dermatomyositis?

Answer 4

DM - immune complex deposition in the perivascular region

PM - direct CD8+ T cell

so they are actually quite different

Question 5

what is the anti-synthetase syndrome?

Answer 5

this is a myositis that is associated with antisynthetase antibodies.

Anti-Jo1 is one such Ab

it is clinically:

• autoimmune myositis
• interstitial lung disease
• inflamm arthritis and fever
• “mechanic’s hands”
• cutaneous vasculitis

Question 6

Are there any dermatomyositis specific antibodies?

Answer 6

anti-MI2 - more severe skin rash, but more responsive to therapy
anti-p155/140 - increased cancer risk

anti-MDA5 - inc. risk of severe ILD

Question 7

What syndrome is associated with anti-SRP (signal recognition peptide)?

Answer 7

necrotising autoimmune myositis syndrome (idiopathic myopathy with nectrotisation)

rapidly progressive

SEVERE muscle weakness

this Ab has also been associated with an anti-HMG-CoA Ab following statin myopathy

Question 8

what is the treatment of myositis?

Answer 8

limited clinical trials

based on expert opinion

often trial steroids; antimetabolites (esp MTX, aza, MMF); cyclophosphamide; cyclosporin

IVIg

rituximab?

rehab eventually

MDT planning

Question 9

what is the association between dermatomyositis (and polymyositis) and malignancy?

Answer 9

it seems to be about 30% for DM and 10% for PM

therefore, when you diagnose someone with these conditions, you should think about CT c/a/p and MMG/breast USS and upper/lower scopes and PSA

Question 10

facial weakness/involvement occurs in which of the myositides?

Answer 10

inclusion body myositis

there is sparing of the face in PM and DM