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rheum.idiopathic-inflammatory-myopathy.core.v1PRODUCTION
rheum.idiopathic-inflammatory-myopathy.core.v1

Idiopathic inflammatory myopathy (myositis)

rheumatologyacutechronicadult
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Detailed

Confirmed/suspected idiopathic inflammatory myopathy in an adult. Pure rhabdomyolysis routes elsewhere; isolated CK without weakness/skin is screened for mimics first

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IIM scope confirmed; not a pure metabolic/toxic rhabdomyolysis presentation

Patient inputs (13)

Detects interstitial lung disease — the leading cause of death (esp anti-MDA5, antisynthetase)

FVC + DLCO baseline + serial; declining FVC = respiratory-muscle weakness or progressive ILD

DM (anti-TIF1γ/NXP2) is paraneoplastic — age-appropriate + targeted screen at diagnosis and surveillance

IBM (>50, treatment-refractory) vs juvenile/adult DM; older age + DM raises malignancy probability

Anti-HMGCR IMNM is statin-associated and PERSISTS after statin stop; excludes toxic/drug myopathy mimic

Symmetric PROXIMAL = DM/PM/IMNM/ASS; asymmetric DISTAL + finger-flexor/quad = IBM (do NOT immunosuppress aggressively)

Gottron/heliotrope/shawl/V/mechanic’s hands/calcinosis define DM and ASS subtypes

Disease activity + subtype clue: very high CK (IMNM), low/normal CK (anti-MDA5 amyopathic DM)

Muscle-source transaminitis/LDH mistaken for liver disease; tracks activity

MSA/MAA define subtype + risk: anti-MDA5 (RP-ILD), anti-Jo1/PL7/PL12 (ASS), anti-SRP/HMGCR (IMNM), anti-TIF1γ/NXP2 (cancer/calcinosis), anti-Mi2 (classic DM)

Pharyngeal/esophageal weakness → aspiration risk; mandates swallow eval + airway precautions

Myocarditis/arrhythmia is a killer; troponin elevation may be cardiac or skeletal-muscle source

Complements CK; can be elevated when CK normal/borderline

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Severity triggers (6)

6 need judgement
  • informationallife_threateningrapidly_progressive_anti_mda5_ild
    Anti-MDA5 (often amyopathic, low CK) with rapidly progressive ILD and hypoxemic respiratory failure
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationallife_threateningrespiratory_muscle_weakness_declining_fvc
    Respiratory-muscle weakness — declining FVC, paradoxical breathing, rising CO2
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationallife_threateningmyositis_myocarditis_arrhythmia
    Myocarditis or significant arrhythmia (elevated cardiac troponin, conduction disease, reduced EF)
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationalseveresevere_dysphagia_aspiration
    Severe pharyngeal/esophageal weakness with aspiration / aspiration pneumonia
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationalsevereparaneoplastic_malignancy_detected
    Malignancy detected at diagnosis/surveillance (esp DM, anti-TIF1γ / anti-NXP2)
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationalmoderateinclusion_body_myositis_misimmunosuppressed
    Asymmetric distal (finger-flexor/quadriceps) treatment-refractory weakness in older patient — IBM mistaken for PM
    Trigger could not be auto-evaluated — needs clinician judgement.

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Recommended regimen

Myositis — severity/subtype triage → GC backbone → steroid-sparer → IVIG → rituximab → anti-MDA5 triple therapy → IBM supportive → cancer-directed
axis: iim_severity_subtype_basedstep 1 - Severity/subtype triage + high-dose glucocorticoid backbone (± pulse MP)
Selected step "Severity/subtype triage + high-dose glucocorticoid backbone (± pulse MP)" — Confirmed IIM (DM / PM / IMNM / antisynthetase) — NOT IBM. Pulse MP reserved for severe: RP-ILD, severe dysphagia, myocarditis, profound weakness
  • methylprednisolone (pulse)
    first line
    corticosteroid
    0.5–1 g IV daily × 3 days • IV • daily × 3 d
    triggers: rapidly_progressive_ILD, severe_dysphagia, myocarditis, profound_proximal_weakness
    2024 IIM management reviews — pulse induction for organ-threatening / severe disease before oral taper
    rxcui 6902
  • prednisone
    first line
    corticosteroid
    1 mg/kg/day (max ~80 mg/d) PO • PO • daily, slow taper over 6–12 months
    triggers: confirmed_IIM_not_IBM
    2017 EULAR/ACR-classified IIM — high-dose oral GC backbone; minimise cumulative dose with early steroid-sparer
    rxcui 8640

outpatient playbook — drug actions (4)

  1. 1. prednisone
    1 mg/kg/d PO, slow taper over 6–12 months • PO • daily, taper
    trigger: Confirmed non-IBM IIM, mild (no organ threat)
    GC backbone (2017 EULAR/ACR IIM)
  2. 2. steroid-sparer (MTX or AZA; MMF if ILD)
    MTX 15–25 mg weekly + folate OR AZA 1.5–2.5 mg/kg/d OR MMF 1–1.5 g BID • PO/SC • weekly/daily/BID
    trigger: Start early to spare steroid
    Early steroid-sparing (2024 reviews)
  3. 3. IVIG
    2 g/kg per cycle monthly • IV • monthly
    trigger: Active DM refractory to GC + steroid-sparer / pregnancy
    ProDERM NEJM 2022
  4. 4. PJP prophylaxis + bone/GIOP protection
    TMP-SMX SS daily if pred >=20 mg >=4 wk; Ca/vit D ± bisphosphonate • PO • daily
    trigger: Prolonged/high-dose steroid
    Infection + bone protection (ACR)

Auto-drafted A&P note

outpatient

Subjective

- Possible entry pathways: Subacute symmetric proximal muscle weakness (difficulty rising from chair, climbing stairs, arms overhead); Elevated CK / aldolase / AST-ALT / LDH without hepatobiliary cause; Gottron papules / heliotrope rash / shawl-V sign / mechanic’s hands.

Objective

- No vitals, labs, or imaging entered for this encounter.

Assessment

**Idiopathic inflammatory myopathy (myositis)** (rheum.idiopathic-inflammatory-myopathy.core.v1).
Phenotype framing: Assign subtype (DM incl. amyopathic/anti-MDA5; PM by exclusion; IMNM anti-SRP/HMGCR; antisynthetase anti-Jo1/PL7/PL12; IBM). Exclude mimics: statin/drug/toxic myopathy, hypothyroid myopathy, metabolic/mitochondrial myopathy, muscular dystrophy, motor neuron disease, myasthenia gravis, rhabdomyolysis, overlap/MCTD
Scope: Confirmed/suspected idiopathic inflammatory myopathy in an adult. Pure rhabdomyolysis routes elsewhere; isolated CK without weakness/skin is screened for mimics first

No severity triggers fired against current inputs.

Plan

Regimen axis: **Myositis — severity/subtype triage → GC backbone → steroid-sparer → IVIG → rituximab → anti-MDA5 triple therapy → IBM supportive → cancer-directed** — step "Severity/subtype triage + high-dose glucocorticoid backbone (± pulse MP)".
1. methylprednisolone (pulse) 0.5–1 g IV daily × 3 days IV daily × 3 d (corticosteroid, first line) — 2024 IIM management reviews — pulse induction for organ-threatening / severe disease before oral taper
2. prednisone 1 mg/kg/day (max ~80 mg/d) PO PO daily, slow taper over 6–12 months (corticosteroid, first line) — 2017 EULAR/ACR-classified IIM — high-dose oral GC backbone; minimise cumulative dose with early steroid-sparer

Setting playbook (outpatient) — Diagnose and treat mild IIM without organ-threatening features (no significant ILD, no dysphagia, no myocarditis), or maintain stable disease/IBM, with steroid-sparing immunosuppression, surveillance, and rehabilitation
3. prednisone 1 mg/kg/d PO, slow taper over 6–12 months PO daily, taper — Confirmed non-IBM IIM, mild (no organ threat) (GC backbone (2017 EULAR/ACR IIM))
4. steroid-sparer (MTX or AZA; MMF if ILD) MTX 15–25 mg weekly + folate OR AZA 1.5–2.5 mg/kg/d OR MMF 1–1.5 g BID PO/SC weekly/daily/BID — Start early to spare steroid (Early steroid-sparing (2024 reviews))
5. IVIG 2 g/kg per cycle monthly IV monthly — Active DM refractory to GC + steroid-sparer / pregnancy (ProDERM NEJM 2022)
6. PJP prophylaxis + bone/GIOP protection TMP-SMX SS daily if pred >=20 mg >=4 wk; Ca/vit D ± bisphosphonate PO daily — Prolonged/high-dose steroid (Infection + bone protection (ACR))

Non-pharmacologic actions:
- Physical + occupational therapy + graded exercise (central in IBM)
- IBM: supportive/assistive devices, dysphagia management — NO aggressive immunotherapy
- Non-live vaccination program
- Cancer surveillance schedule (esp DM anti-TIF1γ/NXP2, first ~3 years)
- Pregnancy planning on compatible agents (AZA / IVIG; avoid MTX/MMF/CYC)

AVOID / contraindication checks:
- Do not aggressively immunosuppress inclusion body myositis — immunotherapy futile/harmful, divert to supportive + exercise (2024 IIM reviews)
- Anti HMGCR IMNM is statin associated and PERSISTS after statin stop — discontinue statin but treat with immunosuppression; do not rechallenge statin (2024 IIM reviews)
- Methotrexate caution/avoid with myositis associated ILD (pneumonitis confounds ILD) and in pregnancy — prefer azathioprine/MMF (2024 IIM reviews)
- Live vaccines contraindicated on immunosuppression (ACR vaccination guidance)
- Cyclophosphamide gonadotoxicity — fertility counselling + MESNA + hydration uroprotection (ACR)
- Azathioprine TPMT/NUDT15 testing before initiation (CPIC/ACR)
- Rituximab HBV screen before dosing (reactivation risk) (2024 IIM reviews)
- PJP prophylaxis when prednisone >=20 mg >=4 weeks or on rituximab/cyclophosphamide/anti MDA5 triple therapy (2024 IIM reviews)

Monitoring

Regimen monitoring:
- CK + manual muscle testing (MMT-8) every 2–4 weeks during induction then per response (2017 EULAR/ACR IIM)
- serial PFTs (FVC + DLCO) + HRCT for ILD activity (2024 IIM reviews)
- repeat swallow evaluation if dysphagia (aspiration risk) (2024 IIM reviews)
- ECG + troponin + echo if cardiac involvement (myocarditis/arrhythmia) (2024 IIM reviews)
- CBC + LFTs for methotrexate/azathioprine/MMF myelo-/hepatotoxicity (ACR)
- infection surveillance on immunosuppression; ferritin + CRP trend in anti-MDA5 RP-ILD (anti-MDA5 ILD evidence)
- ongoing malignancy surveillance — especially DM anti-TIF1γ/NXP2 for the first ~3 years (2024 IIM reviews)

Setting (outpatient) monitoring:
- CK + MMT-8 every 4–8 weeks then per stability (2017 EULAR/ACR IIM)
- PFTs (FVC/DLCO) q3–6 months if ILD; annually if at-risk antibody (2024 reviews)
- CBC + LFTs for steroid-sparer q4–8 weeks (ACR)
- Annual malignancy surveillance for high-risk DM phenotypes × ~3 years (2024 reviews)

Follow-up plan: Lifelong rheumatology/neuromuscular continuity; steroid minimisation + bone/PJP protection; pulmonary follow-up for ILD; cancer surveillance schedule; PT/OT + speech therapy; vaccination (non-live on immunosuppression); pregnancy planning on compatible agents; IBM disability/assistive-device planning
- Close-out criterion: long-term immunosuppression, surveillance, and rehabilitation plan documented

Monitoring phase: CK + manual muscle testing (MMT-8) trend, serial PFTs (FVC/DLCO) + HRCT for ILD, repeat swallow eval, ECG/troponin if cardiac involvement, infection surveillance on immunosuppression, anti-MDA5 ferritin/CRP trend, ongoing cancer surveillance (esp DM anti-TIF1γ/NXP2, first 3 years)

Disposition

Current setting: outpatient — Diagnose and treat mild IIM without organ-threatening features (no significant ILD, no dysphagia, no myocarditis), or maintain stable disease/IBM, with steroid-sparing immunosuppression, surveillance, and rehabilitation

Disposition criteria:
- Continue outpatient unless organ-threatening feature emerges; lifelong rheumatology/neuromuscular continuity (2024 reviews)

Escalation triggers (move to higher acuity):
- New/worsening dyspnea or falling DLCO → urgent HRCT, escalate (RP-ILD risk) (anti-MDA5 ILD evidence)
- New dysphagia → admit + swallow eval + escalate therapy (2024 reviews)
- Cardiac symptoms / troponin rise → ED + cardiology (2024 reviews)
- Rapidly progressive weakness / hypoxemia → ED/ICU (2024 reviews)

Earlier-Return Triggers

Return-precaution thresholds (watch for):
- [LIFE_THREATENING] Anti-MDA5 (often amyopathic, low CK) with rapidly progressive ILD and hypoxemic respiratory failure
- [LIFE_THREATENING] Respiratory-muscle weakness — declining FVC, paradoxical breathing, rising CO2
- [LIFE_THREATENING] Myocarditis or significant arrhythmia (elevated cardiac troponin, conduction disease, reduced EF)

Citations

- 2017 EULAR/ACR IIM classification criteria + 2024 IIM management reviews; ProDERM IVIG NEJM 2022; anti-MDA5 ILD combination-immunosuppression evidence [PMID:29106061](https://pubmed.ncbi.nlm.nih.gov/29106061/)
- Cited evidence (PMID 36198179) [PMID:36198179](https://pubmed.ncbi.nlm.nih.gov/36198179/)
- Cited evidence (PMID 33258553) [PMID:33258553](https://pubmed.ncbi.nlm.nih.gov/33258553/)
- Cited evidence (PMID 32276271) [PMID:32276271](https://pubmed.ncbi.nlm.nih.gov/32276271/)
- Cited evidence (PMID 23124935) [PMID:23124935](https://pubmed.ncbi.nlm.nih.gov/23124935/)

Last reconciled with current guidelines: 2026-05-22.
References
  • 2017 EULAR/ACR IIM classification criteria + 2024 IIM management reviews; ProDERM IVIG NEJM 2022; anti-MDA5 ILD combination-immunosuppression evidence — PMID:29106061
  • Cited evidence (PMID 36198179) — PMID:36198179
  • Cited evidence (PMID 33258553) — PMID:33258553
  • Cited evidence (PMID 32276271) — PMID:32276271
  • Cited evidence (PMID 23124935) — PMID:23124935