Myositis

GRADE 1

Mild pain , mild muscle weakness
Or
CK value < 2,5 ULN

>GRADE 2

• Signs of muscle weakness
• Respiratory symptoms
• Swallowing problems (dysphagia)
• Diplopia possible
• Or CK > 2,5 ULN or elevated troponin

In case of doubt withhold ICPI

Initiate paracetamol/NSAID

If symptom severity increases despite NSAID consider treatment cfr grade 2

Control CK after one week, if increasing: discuss with local myositis specialist

Stop ICPI

Start corticoids 1mg/kg after discussion with internist/rhumatologist/neuromuscular specialist, continue for at least 1 month even if clinical imporvement after 1 week. If needed add other immunsuppressants so corticoids can be tapered after one month

If no improvement after 48h (pain or CK): 2 mg/kg; if still no improvement 48h later, other immunosuppressants should be discussed with experienced organ specialist

Consider IVIG (no reimbursment in Belgium) or bolus steroids if severe life threatening weakness, less evidence for plasma exchange

Complete history of all organ systems

Perform examination of joints and skin

Exclude cardiac origin (CKMB/troponin/pro-BNP and ECG) and in case of doubt perform cardiac IRM

Troponin I is more specific of cardiac involvement than troponin T

Exclude other causes of elevated CK: IM injection, physical activity, …

In addition to analysis for grade I:

Perform EMG to evaluate myopathic features Assesment of diaphragm motion: X ray and perform respiratory tests both in upright and horizontal position

Perform MRI of affected muscle Consider muscle biopsy before start steroids (should be done by experienced specialist)

Analyze serology before start of steroids (ANF (+further subanalysis), myositis specific antibodies / myositis associated antibodies) (according to local practice) Perform spirometry in order to assess restrictive syndrom (due to paralysis of intercostal muscles)