Polymyositis and dermatomyositis Flashcards Preview

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Polymyositis (PM)

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



If there is skin involvement in polymyositis it is 'Dermatomyositis'


Causes of polymyositis

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


Clinical features of adult polymyositis (PM)

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


Clinical features of adult dermatopolymyositis

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


Heliotrope Rash

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


Gottron's Papules

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


Dermatomyositis/Polymyositis and other ARDs

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


Antisynthetase syndrome

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


Cancer risk with PM/DM

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


Childhood Dermatomyositis

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


Blood tests in PM/DM

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


EMG in myositis

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


Other tests for myositis

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


Management of PM/DM

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


Treatment of childhood PM/DM

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


Inclusion body myositis

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


Inclusion bodies

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