Polymyositis and dermatomyositis

Question 1

Polymyositis (PM)

Answer 1

A rare idiopathic disorder characterised by striated muscle inflammation causing proximal muscle weakness

Question 2

Dermatomyositis

Answer 2

If there is skin involvement in polymyositis it is ‘Dermatomyositis’

Question 3

Causes of polymyositis

Answer 3

The incidence is 2-10/million and it occurs in all ages and races – aetiology is unknown but viruses (Coxsackie, rubella, influenza) have been implicated
HLA-B8/DR3 are genetically predisposed

Question 4

Clinical features of adult polymyositis (PM)

Answer 4

M:F/1:3, insidious (months) or acute onset
proximal muscle weakness – shoulder and pelvic girdle muscles may become wasted (but not tender)
can progress to pharyngeal, laryngeal & respiratory muscle weakness
Also malaise, weight loss, fever

Question 5

Clinical features of adult dermatopolymyositis

Answer 5

Heliotrope rash, Gottron’s papules, nailfold erythema.
25% have ulcerative vasculitis and subcut calcinosis
Also myalgia, polyarthritis and Raynaud’s
Long term –> muscle fibrosis and contractures can occur

Question 6

Heliotrope Rash

Answer 6

Purple discolouration of the eyelids which may be accompanied by periorbital oedema
Also pathognomonic for Detmatomyositis

Question 7

Gottron’s Papules

Answer 7

Raised purple-red vasculitic patches on the hands and knuckles which occur in 70% of patients with dermatomyositis – by very specific for the disease

Question 8

Dermatomyositis/Polymyositis and other ARDs

Answer 8

There is an association with other ARDs and both co-mobidities can occur and overlap syndromes

Question 9

Antisynthetase syndrome

Answer 9

20-30% of patients with DM or PM have autoantibodies to tRNA synthetase enzymes (anti-Jo) –> increased risk of pulmonary fibrosis, Raynaud’s, arthritis and ‘mechanic’s hands’’
50% will also have oesophageal involvement
This is a variant syndrome with a poor prognosis due to the combination of pulmonary fibrosis and weakened respiratory muscles

Question 10

Cancer risk with PM/DM

Answer 10

2.4x relative risk for men and 3.4x for women if they have PM/DM –> wide variety of cancers reported
Ca may predate the onset or lag behind it by years but recurrent disease should be investigated for occult malignancy

Question 11

Childhood Dermatomyositis

Answer 11

commonly affects 4-10yrs –> Typical DM rash with muscle weakness –> this can lead to widespread muscle atrophy, subcut calcification and contractions
Ulcerative vasculitis is common as is recurrent abdo pain from vasculitis

Question 12

Blood tests in PM/DM

Answer 12

Muscle enzymes (ALT AST LDH CK aldolase) raised
ESR – not usually raised
Autoantibodies – ANA is often positive as is RF (50%)
Myositis specific antibodies have been recognised as well

Question 13

EMG in myositis

Answer 13

Classic triad of changes: spontaneous fibrilation potentials at rest, polyphasic/short-duration potentials on voluntary contraction and salvoes of repetitive potentials on mechanical stimulation of the nerve

Question 14

Other tests for myositis

Answer 14

MRI – abnormally inflamed muscle
Needle muscle biopsy –> fibre necrosis & regeneration with inflammatory cell infiltrate - can do open biopsy
PET and other imaging to screen for malignancies

Question 15

Management of PM/DM

Answer 15

Prednisolone
Immunosuppressives if resistant: azathioprine, methotrexate, cyclophosphamide, ciclosporin.
Hydroxychlorquine and tacrolimus for skin

Question 16

Treatment of childhood PM/DM

Answer 16

Similar to adults but more aggressive with steroid-sparing immunosuppressants used earlier

Question 17

Inclusion body myositis

Answer 17

Occurs in men over 50yrs – slowly progressive distal muscle weakness with dysphagia from pharyngeal muscle weakness in 50%
EMG shows myopathic and neuropathic changes
Biopsy shows inclusion bodies

Question 18

Inclusion bodies

Answer 18

Under LM – inflammation and basophilic rimmed vacuoles
Under EM – filamentous inclusions and vacuoles
Corticosteroids can be trialed but response is generally poor