Polymyostitis is severe inflammation of proximal striated muscle. DM – when skin is also affected
Etiology
- Virus – coxsachie, rubella, influenza
- HLA DR3 (others = Myasthenia gravis, Hashimoto, T1DM, primary sclerosing cholangitis)
- Can be associated w/ sjogrens, SSc, SLE
CF
- Adult PM
- Female, insidious, malaise, fever, WL, proximal muscle weakness (shoulder)
- Face and distal limbs spared. Larynx/pharynx/respire muscles in advanced disease
- Adult DM
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- Characteristic rash – eyes have purple discolouration and periorbital edema. Gottrons papules – vasculitis patches over knuckles
- Myalgia, polyarthritis, raynauds
- Ulcerative vasculitis and calcinosis of subcutaneous tissue
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- Antisynthase syndrome
- tRNA synthase antibody = poor prognosis, pts develop pulmonary interstitial fibrosis and hand contractures. Dysphagia is also common.
- Childhood DM
- 4-10y, features same as above
Diagnosis
- Creatinine kinase, LDH, aldolase – muscle damage
- Antibodies – tRNA-ab, ANA, RF
- EMG – triad for myositis = 1. spontaneous fibrillations at rest, 2.short PO on contraction, 3. repetitive PO on mechanical nerve stimulation
- PET/malignancy screening
DDx
- All haematological conditions. Auto antibodies and EMG strong evidence for diagnosis.
Treatment
- Prednisolone [0.5-1 mg/kg] until no myositis
- If advanced features use methylprednisolone 1g/day for 3 days
- Steroid sparring – methotrexate [25mg/week], azathioprine, cyclosporin, mycophenolate
- IVIG