What are the inflammatory myopathies?

The idiopathic inflammatory myopathies (IIMs) are rare autoimmune conditions causing immune-mediated skeletal muscle damage. Main types: Dermatomyositis (DM): muscle weakness + pathognomonic skin features (Gottron's papules, heliotrope) + high malignancy association. Anti-synthetase syndrome: myopathy + ILD + arthritis (anti-Jo-1 and other synthetase antibodies). IMNM (immune-mediated necrotising myopathy): severe proximal weakness; very high CK; anti-HMGCR (statin-associated) or anti-SRP. IBM: slowly progressive; elderly men; finger flexors + quadriceps; does not respond to treatment.

How is IBM different and why does it matter clinically?

IBM is crucially different: it does not respond to any immunosuppression — treating IBM with high-dose steroids causes significant harm without benefit. IBM features: selective pattern (finger flexors > shoulder abductors; quadriceps > hip flexors — opposite to symmetric proximal pattern of other IIMs); very slow onset over years; age >50, predominantly men; rimmed vacuoles on biopsy; anti-CN1A antibodies in ~30-40%. Once IBM is confirmed: no steroids, no IVIG, no rituximab — supportive care only (physiotherapy, falls prevention, dysphagia management for severe swallowing difficulty).

What is anti-MDA5 dermatomyositis?

Anti-MDA5 positive DM: clinically amyopathic or hypomyopathic (minimal muscle disease) + rapidly progressive ILD — progressing from normal HRCT to respiratory failure within weeks to months with >50% 6-month mortality without aggressive treatment. Skin features: typical DM skin; mechanic's hands; skin ulceration. Requires: immediate anti-MDA5 testing on DM diagnosis; urgent HRCT; triple immunosuppression (steroids + calcineurin inhibitor + MMF) started immediately ± rituximab/plasma exchange for severe RP-ILD.

Why must all DM adults be screened for cancer?

Approximately 25-30% of adult DM patients have an associated malignancy within 3 years. Mandatory at DM diagnosis: CT chest/abdomen/pelvis; colonoscopy; mammography and pelvic US (women); PSA (men >50); upper GI endoscopy (nasopharyngeal carcinoma in Asian populations). Anti-TIF1γ (~40% malignancy rate) and anti-NXP2 have the highest risk. Successful cancer treatment can sometimes lead to DM remission.

How does GMJ News cover inflammatory myopathy?

GMJ News covers IIM classification, Gottron's + heliotrope as pathognomonic DM, anti-MDA5 RP-ILD emergency, IBM non-response to immunosuppression, malignancy screening in DM, IVIG Grade A evidence, myositis antibody panel, anti-synthetase ILD, statin IMNM, rituximab for refractory, and calcinosis in JDM.

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Inflammatory Myopathy

GMJ News knowledge hub · last reviewed September 2026 · Georgian Medical Journal

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The idiopathic inflammatory myopathies (IIMs) — encompassing dermatomyositis (DM), anti-synthetase syndrome, immune-mediated necrotising myopathy (IMNM) and inclusion body myositis (IBM) — are rare autoimmune conditions causing proximal skeletal muscle weakness, with dermatomyositis characterised by its pathognomonic skin changes (Gottron’s papules over the knuckles; heliotrope rash periocularly) and a clinically important malignancy association (approximately 25-30% of DM patients have an underlying cancer within 3 years of diagnosis), while anti-MDA5 antibody-positive dermatomyositis carries a rapidly progressive interstitial lung disease with over 50% mortality without aggressive immunosuppression (WHO). The most critical clinical distinction is recognising inclusion body myositis (IBM) — the most common myopathy in adults over 50 — which does not respond to immunosuppression (unlike the others) and is characterised by its selective pattern: finger flexor weakness greater than shoulder abductor weakness + quadriceps weakness, a pattern opposite to all other inflammatory myopathies.

Key messages

Gottron's papules + heliotrope rash = dermatomyositis — pathognomonic

Gottron's papules (violaceous papules over MCP/PIP joints — pathognomonic for DM) and heliotrope rash (purple-lilac periorbital discolouration with swelling) are the most specific skin findings in medicine for a systemic diagnosis. Their presence confirms DM even without muscle disease (amyopathic DM).

Anti-MDA5 dermatomyositis — rapidly progressive ILD with >50% mortality

Anti-MDA5 antibody-positive DM: clinically amyopathic (minimal muscle weakness) + rapidly progressive ILD — one of the most feared complications in rheumatology, with >50% mortality within 6 months without aggressive triple immunosuppression (high-dose steroids + cyclosporin/tacrolimus + mycophenolate ± rituximab). Must be identified and treated urgently.

Malignancy association — screen all DM adults at diagnosis

DM is associated with underlying malignancy in approximately 25-30% of adult patients within 3 years of diagnosis. All newly diagnosed DM adults: CT chest/abdomen/pelvis; mammography/pelvic ultrasound (women); PSA (men); upper GI endoscopy. Anti-TIF1γ and anti-NXP2 antibodies carry the highest malignancy risk.

IBM does NOT respond to immunosuppression — the critical distinction

Inclusion body myositis (IBM) — the most common myopathy in adults over 50 — does NOT respond to steroids or immunosuppression. Treating IBM with steroids causes harm without benefit. Distinguishing features: selective pattern (finger flexors > shoulder abductors; quadriceps > hip flexors) — opposite to other IIMs; very slow onset; elderly men; anti-CN1A antibodies in ~30-40%.

Myositis-specific antibodies — the diagnostic game-changer

Anti-Jo-1: anti-synthetase syndrome (myopathy + ILD + arthritis). Anti-MDA5: ADM + RP-ILD (see above). Anti-Mi-2: classic DM, good prognosis, low ILD risk. Anti-TIF1γ: DM + malignancy risk. Anti-HMGCR: statin-IMNM (very high CK >10,000; rituximab + IVIG). Anti-SRP: severe IMNM; cardiac involvement. Anti-CN1A: IBM biomarker.

IVIG — Grade A evidence for refractory dermatomyositis

Cochrane review: IVIG significantly improves muscle strength and CK in refractory DM — one of the clearest Level A evidence bases for IVIG in any autoimmune condition. Dose: 2g/kg per course (divided over 2-5 days), monthly. Also effective: IMNM (anti-HMGCR — combine with rituximab); anti-synthetase syndrome with severe ILD.

Key statistics

~10/100K

annual incidence of IIM; DM most common in adults; IBM most common in >50s

EULAR/ACR

>50%

mortality within 6 months of RP-ILD in anti-MDA5 DM without aggressive treatment

EULAR

25-30%

of adult DM patients have underlying malignancy within 3 years

EULAR/ACR

IBM

does NOT respond to immunosuppression — most common myopathy in adults >50

ENMC/EULAR

>10,000

IU/L CK level typical in anti-HMGCR or anti-SRP IMNM

EULAR/Rheumatology

ACR/EULAR 2017

classification criteria for IIM; MSA-based subclassification

ACR/EULAR 2017

Inflammatory myopathy subtypes — key differentiating features (ACR/EULAR)

Source: ACR/EULAR 2017. IBM most common in elderly; only IIM not responding to immunosuppression.

Glossary of key terms

Gottron's papules and heliotrope rash
Dermatology/RheumatologyGottron's papules: flat-topped, violaceous papules over bony prominences of MCP/PIP joints, elbows, knees or medial malleoli — pathognomonic for DM. Distinguished from psoriasis (at webspaces) and sclerodactyly. Heliotrope rash: purple-lilac upper eyelid discolouration ± periorbital oedema — named after the heliotrope flower. Both can occur without muscle disease (amyopathic DM) and mandate: CK; myositis antibody panel; pulmonary function; HRCT; malignancy screen.

Anti-synthetase syndrome
EULARDefined by anti-aminoacyl-tRNA synthetase antibodies: anti-Jo-1 (most common); anti-PL-7, PL-12, EJ, OJ, KS. Triad: inflammatory myopathy + ILD (most dangerous) + inflammatory arthritis; also: Raynaud's; mechanic's hands (hyperkeratosis, fissuring on radial fingers); fever. ILD is the mortality driver — HRCT essential at diagnosis and follow-up.

Inclusion body myositis (IBM)
ENMC/NeurologyMost common acquired myopathy in adults >50. Distinctive pattern: finger flexor > shoulder weakness (difficulty opening jars) + quadriceps atrophy. EMG: mixed myopathic-neuropathic. Biopsy: rimmed vacuoles + 15-18nm tubulofilamentous inclusions. Anti-CN1A antibodies: ~30-40%. No treatment has demonstrated benefit — steroids, IVIG, rituximab, MTX all negative in RCTs. Management: supportive (physiotherapy, falls prevention, dysphagia management).

Anti-HMGCR statin-IMNM
Rheumatology/PharmacologyStatin use upregulates HMGCR expression in regenerating muscle → immune response → IMNM persists even after statin cessation (HMGCR expressed in healing muscle regardless of statin). Very high CK (>10,000). Also occurs without statin exposure. Treatment: stop statin + IVIG + high-dose steroids; rituximab for refractory. Slow response.

Myositis antibody panel
EULAR/LaboratoryLine blot assay detects 16+ specificities: MSAs (myositis-specific antibodies): anti-Jo-1; anti-MDA5 (RP-ILD); anti-Mi-2 (classic DM, good prognosis); anti-TIF1γ (malignancy); anti-NXP2 (malignancy, calcinosis); anti-SRP (severe IMNM, cardiac); anti-HMGCR (statin IMNM). MAAs (myositis-associated): anti-Ro52 (ILD, anti-synthetase co-marker). Essential for subtype classification and prognosis.

Calcinosis in JDM
Paediatrics/RheumatologyCalcinosis (subcutaneous calcium deposits) occurs in approximately 30% of juvenile dermatomyositis (JDM) — much more common than in adult DM. Calcium deposits form in skin, subcutaneous tissue and muscle — can be painful, ulcerate and cause contractures. Associated with anti-NXP2 antibodies. Partially prevented by aggressive early treatment. Management: aluminium hydroxide; probenecid; bisphosphonates; infliximab — all with limited evidence.

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