Musc dis- Polymyositis Flashcards
what is polymyositis
idiopathic inflammatory myopathy that causes symmetrical, proximal muscle weakness.
risk factors (3)
women (2:1 ratio)
older than 20 years
45-60 years
pathogenesis (2)
T-cell–mediated cytotoxic process directed against unidentified muscle antigens.
CD8 T cells, along with macrophages, initially surround healthy nonnecrotic muscle fibers and eventually invade and destroy them.
presentation/ symptoms
symmetrical, proximal muscle weakness in the upper and lower extremities.
insidious in onset
commonly noticed as difficulty with particular activities e.g. climbing stairs. Some patients have myalgia.
Dysphagia secondary to oropharyngeal and esophageal involvement occurs in about one third of patients with polymyositis and is a poor prognostic sign.
Interstitial lung disease occurs in 5-30% of patients ( especially those positive for anti-Jo-1 antibody).
investigations- antibodies/ bloods
Inflammatory markers are often raised.
Serum creatine kinase (CK) level is usually raised, often more than 10 times the normal level.
Autoantibodies include ANA, anti-Jo-1 and anti-SRP.
investigations- scans/ other tests diagnosis (3)
MRI show signal intensity abnormalities of muscle due to inflammation, oedema, or scarring.
Electromyographic (EMG) abnormal in almost all patients (90%) with polymyositis.
DIAGNOSIS- Muscle biopsy shows muscle fibres in varying stages of inflammation, necrosis, and regeneration.
management (4)
prednisolone (initially around 40mg) combined with immunosuppressive drugs such as methotrexate or azathioprine.
30% of patients are left with some residual weakness, however.