Polymyositis and Dermatomyositis

Question 1

What is polymyositis?

Answer 1

An idiopathic inflammatory myopathy causing symmetrical, proximal muscle weakness

Question 2

How does dermatomyositis differ from polymyositis?

Answer 2

Dermatomyositis includes cutaneous manifestations in addition to muscle weakness

Question 3

What is the common age and gender affected by polymyositis/dermatomyositis?

Answer 3

Females (2:1 ratio), peak incidence ages 40-50

Question 4

What is the key autoimmune mechanism in polymyositis?

Answer 4

T cell-mediated attack on muscle antigens, involving CD8+ T cells and macrophages

Question 5

What are the main clinical features of polymyositis?

Answer 5

(1) Symmetrical
(2) proximal muscle weakness with gradual onset

Question 6

What is Gottron’s sign?

Answer 6

A rash over the knuckles, characteristic of dermatomyositis

Question 7

Name an antibody associated with interstitial lung disease in myositis patients

Answer 7

Anti-Jo-1 antibody

Question 8

First-line investigation for polymyositis and dermatomyositis?

Answer 8

Blood test for creatine kinase (CK)
= typically elevated

Question 9

What is the gold standard diagnostic test for polymyositis/dermatomyositis?

Answer 9

Muscle biopsy

= shows perivascular inflammation and necrosis

Question 10

What is the primary treatment for polymyositis/dermatomyositis?

Answer 10

Prednisolone (first-line)

with the possible addition of methotrexate or rituximab if unresponsive

Question 11

What are common cutaneous signs in dermatomyositis?

Answer 11

Gottron’s sign
Heliotrope rash
Shawl sign

Question 12

What are the first and second-line treatments for polymyositis and dermatomyositis?

Answer 12

First-line: Prednisolone +/- methotrexate

Second-line: Rituximab or other immunosuppressive therapies

Question 13

Name a syndrome associated with myositis and its key features

Answer 13

Anti-synthetase syndrome

= includes mechanic’s hands, Raynaud’s phenomenon, myositis, interstitial lung disease, and polyarthritis

Question 14

What symptom may suggest early dermatomyositis involvement?

Answer 14

Difficulty with activities like brushing hair or climbing stairs due to proximal muscle weakness

Question 15

What physical tests assess muscle strength in myositis?

Answer 15

(1) Confrontational testing (direct power)

(2) Isotonic testing (e.g., 30-second sit-to-stand)

Question 16

What is the “shawl sign” in dermatomyositis?

Answer 16

A reddish-purple rash over the shoulders and upper back

Question 17

Which muscle enzyme is a key indicator of disease activity in polymyositis and dermatomyositis?

Answer 17

Creatine kinase (CK)

Question 18

How can dermatomyositis be present on the hands?

Answer 18

Gottron’s papules (scaly, erythematous knuckle lesions)

Question 19

Name two myositis-specific autoantibodies.

Answer 19

Anti-Jo-1 and anti-SRP

Question 20

What is the significance of a high creatine kinase (CK) level in myositis?

Answer 20

Diagnostic for muscle inflammation, often 10x the normal limit

Question 21

Which antibodies are characteristically associated with dermatomyositis?

Answer 21

Anti Mi-2 and ANA (more common)

Question 22

What is the antibody associated with the extra-muscular features of dermatomyositis?

Answer 22

anti-Jo1

Question 23

Which antibodies are characteristically associated with polymyositis?

Answer 23

anti-Jo1

Question 24

What are the features of polymyositis?

Answer 24

Diffuse proximal muscle weakness.

Question 25

Second-line investigation for polymyositis and dermatomyositis?

Answer 25

Autoantibodies:

= Myositis specific - Anti-Jo-1, anti-SRP
= Non-specific - ANA, anti-RNP

Question 26

2nd line test after muscle biopsy

Answer 26

MRI