Inflammatory myopathies

Question 1

Define Idiopathic inflammatory myopathies

Answer 1

Proximal muscle weakness due to autoimmune-mediated inflammation either with (dermatomyositis) or without (polymyositis) a rash

Question 2

What are the groups of Idiopathic inflammatory myopathies

Answer 2

1. Polymyositis (autoimmune pathogenesis) - muscle involvement
2. Dermatomyositis (autoimmune pathogenesis) - muscle and skin involvement
3. Inclusion body myositis (autoimmune and degenerative pathogenesis)

Question 3

Aetiology of Idiopathic inflammatory myopathies

Answer 3

Unknown
Suggested:
- Infection: several viruses, such as coxsackie, influenza, retroviruses, cytomegalovirus, EBV
- Genetic: HLA subtypes increase risk
- Environmental: UV radiation intensity, hydroxyurea
- Immunological: various autoantibodies e.g. antisynthetases anti-Jo-1 antibodies

Question 4

Risk factors for inflammatory myopathies

Answer 4

Children and age >40
Exposure to high intensity of global UV radiation
Genetic predisposition
Female sex and/or black ethnicity (polymyositis and dermatomyositis)
Male sex and/or white ethnicity (inclusion body myositis)
Lipid lowering agents, HIV, viral infections, non-viral infection, vaccination, drugs and toxin

Question 5

Symptoms of Idiopathic inflammatory myopathies

Answer 5

Proximal myopathy:
- Weakness in the upper extremities but NO pain
- Difficulty with motor tasks e.g. getting up from a chair, climbing steps, lifting objects, combing hair
- Frequent falls
Skin:
- Lilac-coloured (heliotrope) rash on eyelids, malar region and naso-labial folds
- Red or purple flat or raised lesions on knuckles (Gottron’s papules)
- Subcutaneous calcinosis
- Mechanic’s hands (fissuring and cracking of skin over finger pads)

Constitutional: weight loss, fatigue, malaise, fever

Dysphagia, myalgia, arthralgia, palpitations, syncope, MI symptoms, facial rash, erythematous rash, nail fold changes, facial muscle weakness, skin calcinosis, joint swelling

Question 6

Signs of Idiopathic inflammatory myopathies

Answer 6

Lilac-coloured (heliotrope) rash on eyelids, malar region and naso-labial folds
Red or purple flat or raised lesions on knuckles (Gottron’s papules)
Subcutaneous calcinosis
Mechanic’s hands (fissuring and cracking of skin over finger pads)
Shawl sign (apparent sunburn in the distribution of a shawl)
Prominent nail fold capillary loops
Symmetrical peri-ungual erythema and erythema on joints
Muscle weakness
Muscle atrophy (quadriceps, distal wrist, finger flexor)

Question 7

Investigations for inflammatory myopathies

Answer 7

CK/CPK: raised (esp. polyM)
Antibodies: anti-Jo1, anti-Mi2, anti-SRP
Muscle: LDH/ALT/AST elevated
Adolase: raised
Myoglobin: raised
ESR: raised
ANA: positive

EMG: myopathic motor units with early recruitment on voluntary activity
Muscle biopsy: definite diagnosis (inflam infiltrates, CD4 (derm) CD8 (poly) necrosis, atrophy)

Question 8

Management for inflammatory myopathies

Answer 8

Screen for malignancy
Immunosuppression (steroids, cytotoxic agents: azathioprine, methotrexate)
- Prednisolone
- Hydroxychloroquine
- Methotrexate

Question 9

Complications of inflammatory myopathies

Answer 9

Malignancy (10-15%)
Pulmonary fibrosis