Muscle pathology – Patient unstable
October 17, 2026Myocarditis algorithm - Patient is stable
Assess severity + IC-OS diagnostic criteria for myocarditis
Diagnostic confirmation (IC-OS criteria) ?
IC-OS myocarditis diagnostic criteria:
- Histological diagnosis
OR
- Clinical diagnosis (Troponin elevation AND 1 major criteria OR 3 minor criteria)
- Major criteria: positive MRI (Lake Louise criteria)
- Minor criteria
- Cardiomuscular symptoms
- Ventricular arrythmia or new conduction block
- Decline in LVEF
- Presence of myositis or other irAE
- suggestive MRI
Severe if any of:
- Symptomatic patients.
- Troponin > 32* ULN.
- New LVEF degradation.
Is the patient severe ? YES
Severe definitive myocarditis
Treat immediately
- Telemetry/ICU + urgent specialist input
- Permanently stop ICI
- Prednisone 1–2 mg/kg within 24 h
- Reassess Troponin levels after +/- 12, 24 and 36h
- Consider ruxolitinib or MMF
No response at 48 h: pulse steroids ± abatacept/ruxolitinib
Slow taper if improving
Severe possible myocarditis
Treat rapidly and reassess diagnosis
- Consider telemetry/ICU
- Withhold ICI pending diagnosis
- Consider prednisone 1–2 mg/kg if no alternative diagnosis
- Reassess Troponin levels after +/- 12, 24 and 36h
- Consider ruxolitinib or MMF
No response at 48 h: reassess diagnosis before escalading to 2mg/kg prednisone and/or add ruxolitinib or MMF
Slow taper if improving
Is the patient severe ? NO
Non-severe and smoldering definitive
- Withhold ICI
- Prednisone 1 mg/kg
- + reassess troponin levels after +/- 24 and 48h
No response at 48 h: reassess then escalate to 1–2 mg/kg and/or add ruxolitinib or MMF
Slow taper if improving
Isolated Troponin
of unknown significance
- Seek alternative diagnosis
- Consider withholding ICI pending diagnosis
- Repeat CK and troponin I or T in 24 h
Monitor troponin levels at each subsequent ICI cycle.