Inflammatory myositis.
Inflammatory myositis is a group of autoimmune muscle diseases: polymyositis (PM), dermatomyositis (DM), immune-mediated necrotizing myopathy (IMNM), and inclusion body myositis (IBM). Most cause progressive proximal muscle weakness with elevated CK. Dermatomyositis adds characteristic skin findings. MDA5 dermatomyositis carries a high risk of rapidly progressive ILD. Treatment uses steroids, IVIG, methotrexate, mycophenolate, rituximab — but the HI-STIM trial showed high-intensity resistance training is safe and effective. Exercise is not the enemy.
The mechanism, the four faces of myositis.
Inflammatory myositis is not one disease — it's a family. The mechanism and treatment depend heavily on which type:
Polymyositis (PM)
T-cell-mediated muscle damage. Proximal weakness with elevated CK. Often associated with anti-synthetase syndrome (anti-Jo-1, anti-PL-7) which carries high ILD risk.
Dermatomyositis (DM)
Complement-mediated microvascular muscle damage. Classic skin findings (Gottron's papules, heliotrope rash, V-sign, shawl sign). MDA5+ subtype is rapidly progressive ILD until proven otherwise.
Immune-mediated necrotizing myopathy (IMNM)
Necrotizing autoantibody-mediated disease. Anti-HMGCR (statin-triggered) or anti-SRP. Very high CK, severe weakness, often less responsive to steroids alone.
Inclusion body myositis (IBM)
Distinct: older onset, distal as well as proximal weakness, finger flexor weakness, falls. Doesn't respond well to immunosuppression — exercise is the foundation.
The 4-step plan, applied to Myositis.
Get the right diagnosis
CK, aldolase, LDH, AST/ALT, myositis-specific antibody panel (Jo-1, PL-7, MDA5, NXP2, TIF1-γ, HMGCR, SRP, Mi-2), MRI of involved muscle, EMG, and muscle biopsy when needed. HRCT chest and PFTs at diagnosis — especially urgent in MDA5+ DM. The myositis antibody panel changes management.
Learn more about labs →Clean up your food
Anti-inflammatory Mediterranean pattern. Adequate protein (1.2–1.6 g/kg/day) supports muscle preservation, especially when on steroids. Monitor swallow function in active disease — pureed diet if dysphagic.
Myositis & diet →Detox your daily life
Statins can trigger anti-HMGCR IMNM — always review with statin exposure in mind. Smoking is associated with anti-synthetase syndrome. UV exposure can flare DM skin disease.
Myositis & environment →Build a stronger body
The HI-STIM trial showed high-intensity resistance training at 80% 1RM × 16 weeks improved MMT8, SF-36, and function in PM/DM/IMNM patients — with zero increase in CK or disease activity. Exercise is safe and effective when supervised. IBM patients especially benefit from structured strength training.
Myositis & exercise →
Go deeper.
Common misconceptions.
"Myositis is just one disease."
It's a family of four distinct entities (PM, DM, IMNM, IBM) with different mechanisms, different antibodies, and different treatments. Calling them all 'myositis' without subtyping leads to wrong treatment. The myositis-specific antibody panel changes management.
"Exercise is dangerous when CK is elevated."
The HI-STIM trial settled this. 60 patients with active PM/DM/IMNM did 16 weeks of high-intensity resistance training at 80% of one-rep max. Zero increase in CK. Zero disease flares. Significant gains in strength, function, and quality of life. Sustained at one-year follow-up. Exercise is medicine.
"Steroids will fix it."
PM and DM often respond to steroids initially, but most patients need a steroid-sparing agent (methotrexate, mycophenolate, rituximab, IVIG). IMNM is often steroid-refractory and requires IVIG plus immunosuppression. IBM doesn't respond to immunosuppression at all — exercise is the foundation.
When to see a rheumatologist.
See a rheumatologist if you have:
- Progressive proximal muscle weakness (difficulty climbing stairs, rising from a chair, lifting arms overhead)
- Elevated CK on a routine lab
- Characteristic dermatomyositis skin findings (Gottron's papules, heliotrope rash, V-sign)
- Unexplained ILD with proximal weakness
- New dysphagia plus muscle weakness
- Statin myopathy that doesn't resolve with statin discontinuation
- Mechanic's hands (cracked, fissured fingertips)
Myositis-specific antibodies guide diagnosis and prognosis. A myositis-suspected workup without the antibody panel is incomplete.
- Jensen KY, et al. High-intensity resistance training in adults with inflammatory myopathy (HI-STIM). Rheumatol Int, 2024. PMC11392978
- Jensen KY, et al. HI-STIM 1-year follow-up. 2025. PMC12003461
- Lundberg IE, et al. 2017 EULAR/ACR classification criteria for idiopathic inflammatory myopathies. Arthritis Rheumatol, 2017. PubMed 29106061
- Allenbach Y, et al. Anti-HMGCR myopathy and statins. Brain.