Idiopathic Inflammatory Myopathies

Question 1

What are IMMs?

Answer 1

Autoimmune disorder where there is inflammation within the muscles

Polymyositis- chronic inflammation of muscles

Dermatomyositis- inflammation of skin and muscles

Question 2

What are the symptoms of polymyositis?

Answer 2

Proximal muscle weakness
No pain
Muscle wasting 
Acute/insidious onset
Weight loss
Fever

Difficulty squatting and climbing stairs

Question 3

What are symptoms of dermatomyositis?

Answer 3

Gottrons lesions
-scaly erythematous patches on knuckles/elbows/knees

Heliotropic rash

Photosensitive rash on back/shoulders/neck

Periorbital oedema

Sc calcinosis

PLUS polymyositis symptoms

Question 4

What investigations are needed?

Answer 4

Bloods
-Serum CK >1000 due to muscle damage

ANA- most +ve
RF- 50% +ve

Myositis specific antibodies

• Anti- Jo1= polymyositis
• Anti-Mi 2= dermatomyositis
• ANA= dermatomyositis

EMG

MRI for abnormal muscle

Muscle biopsy- fibre necrosis with inflammatory infiltrate

Question 5

How is it diagnosed?

Answer 5

The following must be present

• Clinical presentation
• Elevated CK
• Autoantibodies
• Supportive EMG

Question 6

What is the management?

Answer 6

Steroids e.g. prednisolone
Other therapies if steroid response is poor
-DMARDs e.g. azathioprine 
-IV immunoglobulins
-Biological therapy e.g. infliximab

Must screen for appropriate cancers as increased risk

If untreated polymyositis can affect resp muscles causing resp failure

Question 7

What is inclusion body myositis?

Answer 7

Affects white males>50

Insidious onset of proximal and distal muscle wasting- can be asymmetrical

Muscle biopsy shows inflammatory infiltrate and vacuoles containing beta amyloid

Rarely responses to steroids etc.