Dermatomyositis & Polymyositis
Inflammatory myopathies causing proximal muscle weakness. DM has characteristic skin findings (heliotrope rash, Gottron papules). Elevated CK. Associated with malignancy (DM). EMG and muscle biopsy confirm diagnosis. Steroids first-line.
🔍 Overview
Dermatomyositis vs Polymyositis
| Feature | Dermatomyositis | Polymyositis |
|---|---|---|
| Skin findings | Heliotrope rash (purple eyelid discoloration), Gottron papules (papules over MCP/PIP/knuckles), V-sign, shawl sign, mechanic's hands | None |
| Muscle weakness | Proximal, symmetric, progressive | Proximal, symmetric, progressive |
| Histology | Perimysial inflammation, perifascicular atrophy | Endomysial inflammation, CD8+ T cells invading fibers |
| Malignancy | Strong association -screen for ovarian, lung, breast, GI, lymphoma | Weaker association |
| Antibodies | Anti-Mi-2, anti-MDA5, anti-TIF1-γ (malignancy-associated) | Anti-Jo-1 (antisynthetase syndrome: ILD, arthritis, mechanic's hands) |
DM in adults requires age-appropriate malignancy screening. Anti-TIF1-γ antibody is specifically associated with malignancy-associated DM. Screen with CT chest/abdomen/pelvis, mammogram, colonoscopy, and pelvic exam.
Inclusion Body Myositis (IBM)
| Feature | Inclusion Body Myositis |
|---|---|
| Age | >50 years. Most common inflammatory myopathy in elderly. |
| Pattern | ASYMMETRIC, distal + proximal. Finger flexors, wrist flexors, quadriceps ("Can't grip, can't walk"). |
| CK | Mildly elevated or normal |
| Key feature | Does NOT respond to immunosuppression (unlike DM/PM) |
| Histology | Endomysial inflammation + rimmed vacuoles + amyloid deposits |
| Treatment | No effective treatment. PT/OT. IVIG may help swallowing. |
Skin Findings in Detail (Dermatomyositis)
- Heliotrope rash: Purple/lilac discoloration of eyelids, often with periorbital edema. Pathognomonic for DM.
- Gottron papules: Erythematous/violaceous papules over MCP, PIP, DIP joints and knuckles. Pathognomonic.
- Gottron sign: Flat erythematous patches over elbows, knees, medial malleoli.
- V-sign: Erythema over anterior neck/chest in V-distribution.
- Shawl sign: Erythema over upper back and shoulders.
- Mechanic's hands: Rough, cracked, hyperkeratotic skin on radial side of fingers. Associated with antisynthetase syndrome.
- Holster sign: Erythema over lateral thighs.
- Periungual erythema: Dilated nailfold capillaries.
- Calcinosis cutis: Calcium deposits under skin, more common in juvenile DM.
Mnemonic: HELIOGRAMS
Heliotrope rash, Erythema (V-sign), Limbs (Gottron), Interstitial lung disease, Other autoimmune, Gottron papules, Raynaud, Arthritis, Mechanic's hands, Shawl sign
🚨 Management
Treatment
- First-line: Prednisone (Deltasone) 1 mg/kg/day × 4–6 weeks, then taper
- Steroid-sparing: Methotrexate (Trexall) or Azathioprine (Imuran)
- Refractory: Rituximab (Rituxan), IVIG, Mycophenolate (CellCept)
- ILD management: If antisynthetase syndrome -mycophenolate, rituximab, or cyclophosphamide
- Physical therapy -maintain function during and after treatment
- Malignancy screening -age-appropriate, especially in DM
📋 Case 1, Classic Dermatomyositis
Patient: 42F presents with progressive proximal weakness × 2 months, cannot climb stairs or lift arms overhead. Purple discoloration of eyelids, papules over knuckles. CK 8,500.
Action:
- Classic dermatomyositis. Heliotrope rash + Gottron papules + proximal weakness + elevated CK.
- Order: Myositis-specific antibodies (including anti-TIF1-γ), EMG, MRI thighs, age-appropriate malignancy screening.
- Start prednisone 1 mg/kg/day.
- Anti-TIF1-γ positivity → intensive cancer screening: CT chest/abdomen/pelvis, mammogram, colonoscopy, pelvic exam.
- PFTs at baseline for ILD screening.
📋 Case 2, Antisynthetase Syndrome with ILD
Patient: 58F with DM, anti-Jo-1 positive. Develops progressive dyspnea, dry cough. PFTs show restrictive pattern. HRCT: ground-glass opacities, NSIP pattern.
Diagnosis: Antisynthetase syndrome with ILD.
Action:
- ILD is the main driver of mortality in antisynthetase syndrome -not the myopathy.
- Treatment: Steroids + mycophenolate or rituximab for ILD.
- Avoid methotrexate (can cause drug-induced ILD).
- Serial PFTs q3–6 months to monitor progression.
- Look for other features: mechanic's hands, Raynaud, arthritis, fever.
📋 Case 3, Inclusion Body Myositis
Patient: 72M with 2-year history of progressive difficulty opening jars, frequent falls. Asymmetric weakness, finger flexor weakness, quadriceps atrophy. CK 450 (mildly elevated). Failed 6-month trial of prednisone.
Biopsy: Rimmed vacuoles.
Diagnosis: Inclusion body myositis.
Action:
- No effective immunosuppressive treatment -IBM does not respond to steroids, MTX, or azathioprine.
- PT/OT for functional maintenance and fall prevention.
- Swallowing evaluation -dysphagia is common. IVIG may help swallowing.
- Key distinguishing features: age >50, asymmetric, distal involvement (finger flexors), quadriceps atrophy, failed immunosuppression, rimmed vacuoles on biopsy.
🧪 Workup
- CK -elevated (usually > 10× normal). Primary marker of muscle damage.
- Aldolase -elevated (more specific for muscle, also elevated)
- Myositis-specific antibodies -Anti-Jo-1, anti-Mi-2, anti-MDA5, anti-SRP, anti-TIF1-γ
- EMG -myopathic pattern (short, small, polyphasic motor units, fibrillation potentials)
- MRI of thighs -STIR sequences show edema in affected muscles. Can guide biopsy site.
- Muscle biopsy -gold standard for diagnosis and classification
- PFTs -ILD screening (anti-Jo-1)
- Malignancy screening -CT, mammogram, colonoscopy
💊 Medications
| Drug | Dose | Role |
|---|---|---|
| Prednisone (Deltasone) | 1 mg/kg/day | First-line. Taper over months once CK normalizes and strength improves. |
| Methotrexate (Trexall) | 15–25 mg weekly | Steroid-sparing. Give with folic acid. Avoid in ILD (can cause drug-induced ILD). |
| Azathioprine (Imuran) | 2–3 mg/kg/day | Steroid-sparing alternative. Check TPMT. |
| IVIG | 2 g/kg over 2–5 days monthly | Refractory cases, especially DM |
| Rituximab (Rituxan) | 375 mg/m² × 4 weekly | Refractory myositis, antisynthetase-associated ILD |
📋 On Rounds
Pimp Questions
How do you distinguish myositis from steroid myopathy during treatment?
This is a critical clinical challenge. Both cause proximal weakness. Myositis flare: CK is elevated/rising, inflammatory markers up. Steroid myopathy: CK is NORMAL, no inflammatory markers. Steroid myopathy is painless. If CK is normal but weakness persists/worsens, consider reducing steroids. If CK is rising, the myositis is active and steroids may need to be increased or a steroid-sparing agent added.
What is antisynthetase syndrome?
A clinical syndrome associated with anti-aminoacyl-tRNA synthetase antibodies (most commonly anti-Jo-1). Features: (1) ILD (interstitial lung disease -often the dominant and most life-threatening feature), (2) Inflammatory myopathy, (3) Mechanic's hands (cracked, rough skin on palms/fingers), (4) Arthritis, (5) Raynaud phenomenon, (6) Fever. ILD drives prognosis -PFTs and CT chest are essential at diagnosis.
How do you differentiate DM/PM from inclusion body myositis?
IBM: age >50, ASYMMETRIC weakness (unlike DM/PM which is symmetric), involves DISTAL muscles (finger flexors, wrist flexors -"can't make a fist"), quadriceps atrophy ("falls going downstairs"), CK only mildly elevated or normal, does NOT respond to steroids or immunosuppression. Biopsy: rimmed vacuoles + amyloid. Most common inflammatory myopathy in elderly men.
What antibody is most associated with cancer in dermatomyositis?
Anti-TIF1-γ (anti-p155/140). This antibody has the strongest association with malignancy-associated DM. Patients with anti-TIF1-γ need intensive cancer screening: CT chest/abdomen/pelvis, mammogram, colonoscopy, pelvic exam, and age-appropriate screening. Some guidelines recommend repeating screening annually for 3–5 years.
⚡ Summary
The Shared Feature
Proximal, symmetric, progressive muscle weakness: difficulty rising from a chair, climbing stairs and lifting the arms overhead. Weakness rather than pain is the complaint, and a patient whose main symptom is muscle pain with normal strength usually has something else.
Dermatomyositis Is Recognized by the Skin
Heliotrope rash, violaceous discoloration of the eyelids with periorbital edema. Gottron papules over the knuckles (the extensor surfaces, which is what distinguishes them from the lupus rash that spares them). Also the shawl and V signs, mechanic's hands, periungual telangiectasia and calcinosis. Polymyositis has no skin findings.
Confirm It in Four Steps
CK, aldolase, LDH and transaminases raised (a raised AST and ALT from muscle is often mistaken for liver disease). EMG shows an irritable myopathy. MRI identifies edema and the right site to biopsy. Muscle biopsy is definitive. Histology separates them: dermatomyositis shows perimysial inflammation with perifascicular atrophy, a complement-mediated microangiopathy; polymyositis shows endomysial CD8 T cells invading intact fibers.
Screen Adults With DM for Cancer
Dermatomyositis carries a strong malignancy association, and the myositis can precede the cancer by months. Anti-TIF1-gamma antibody specifically marks malignancy-associated disease. Do age-appropriate screening plus CT chest, abdomen and pelvis, mammography, colonoscopy and a pelvic examination, repeated over the first few years. Ovarian, lung, breast, gastrointestinal and lymphoma are the usual suspects.
Let the Antibodies Predict the Complications
Anti-Jo-1 and the other antisynthetases mean antisynthetase syndrome: interstitial lung disease, arthritis, mechanic's hands, Raynaud and fever. Anti-MDA5 means rapidly progressive ILD, often with little muscle involvement and normal CK, and it carries high mortality, so it needs aggressive early treatment. Anti-Mi-2 predicts classic skin disease and a good treatment response.
Screen the Lungs and the Swallow
Interstitial lung disease is the leading cause of death, so get PFTs with DLCO and a high-resolution CT at baseline, not only when the patient is breathless. Dysphagia from pharyngeal and esophageal muscle involvement causes aspiration and predicts a worse outcome, so ask about it directly and get a swallow evaluation.
Treat With Steroids Plus a Sparing Agent From the Start
Prednisone 1 mg/kg/day, tapering slowly over months. Add methotrexate or azathioprine early rather than waiting for steroid failure, because the required steroid course is long and the toxicity is what limits it. IVIG for refractory disease, severe dysphagia and for dermatomyositis skin disease; rituximab and mycophenolate for resistant cases, mycophenolate being preferred where there is ILD. Add sun protection and hydroxychloroquine for the rash, plus physical therapy from the outset, and PJP prophylaxis with prolonged high-dose steroids.
Consider Inclusion Body Myositis in the Non-Responder
Older than 50, slowly progressive, asymmetric, with distinctive involvement of finger flexors and quadriceps. It does not respond to immunosuppression, so a patient labeled as refractory polymyositis often has IBM instead. Biopsy shows rimmed vacuoles. Also exclude the commoner mimics before committing to long-term steroids: statin myopathy (including anti-HMGCR immune-mediated necrotizing myopathy, which does respond to treatment), hypothyroidism, and hereditary myopathy.
📄 One Pager
Text version
RHEUMATOLOGY · One Pager
Dermatomyositis & Polymyositis
Proximal, symmetric, progressive weakness with a high CK. The skin decides DM vs PM, the antibody tells you what else to look for, and in adult DM that means looking for cancer.
Skin Findings: What Separates DM from PM
- Heliotrope rash: purple/lilac discoloration of the eyelids, often with periorbital edema. Pathognomonic for DM.
- Gottron papules: erythematous/violaceous papules over MCP, PIP, DIP joints and knuckles. Pathognomonic.
- Gottron sign: flat erythematous patches over elbows, knees, medial malleoli (a patch, not a papule).
- V-sign, shawl sign, holster sign: erythema over anterior neck/chest, upper back/shoulders, lateral thighs.
- Mechanic's hands: rough, cracked, hyperkeratotic skin on the radial fingers. Points you toward antisynthetase syndrome, so check PFTs.
- Polymyositis: no skin findings at all. Histology also splits them: DM is perimysial with perifascicular atrophy, PM is endomysial with CD8+ T cells invading fibers.
Myositis Antibodies: What Each Predicts
- Anti-TIF1-γ (anti-p155/140): strongest association with malignancy-associated DM. A positive result changes the workup, not just the label: it triggers intensive cancer screening.
- Anti-Jo-1: antisynthetase syndrome, ILD + inflammatory myopathy + mechanic's hands + arthritis + Raynaud + fever. The ILD, not the myopathy, drives prognosis.
- Anti-Mi-2, anti-MDA5: DM-associated myositis-specific antibodies; send with the panel at diagnosis.
- Anti-SRP: part of the myositis-specific antibody panel sent at workup.
- Seronegative does not exclude: the panel is for phenotyping and risk-stratifying, biopsy remains the gold standard for diagnosis and classification.
Workup and Treatment, Step by Step
1
Confirm muscle injury: CK, usually > 10× normal, is the primary marker of muscle damage. Aldolase is also elevated and is more specific for muscle.
2
Localize it: EMG shows a myopathic pattern (short, small, polyphasic motor units with fibrillation potentials). MRI thighs on STIR shows edema in affected muscles and can guide the biopsy site so you do not sample uninvolved muscle.
3
Muscle biopsy: the gold standard for both diagnosis and classification, and the only way to catch the rimmed vacuoles of IBM before you commit someone to months of immunosuppression.
4
Start prednisone 1 mg/kg/day × 4–6 weeks, then taper over months once CK normalizes and strength improves. Taper by response, not by calendar.
5
Add a steroid-sparing agent: methotrexate or azathioprine, to get the patient off high-dose steroids. Add physical therapy to maintain function during and after treatment.
6
Screen in parallel: age-appropriate malignancy screening (especially in DM) and baseline PFTs for ILD. Do not wait until the myopathy is controlled to do these.
Key Drugs
Prednisone (Deltasone)1 mg/kg/day, first-line; taper over months once CK normalizes and strength improves
Methotrexate (Trexall)15–25 mg weekly, steroid-sparing; give with folic acid; avoid in ILD (can cause drug-induced ILD)
Azathioprine (Imuran)2–3 mg/kg/day, steroid-sparing alternative; check TPMT first
IVIG2 g/kg over 2–5 days monthly, for refractory disease, especially DM
Rituximab (Rituxan)375 mg/m² × 4 weekly, for refractory myositis and antisynthetase-associated ILD
Mycophenolate (CellCept)refractory disease and antisynthetase ILD, where methotrexate is the wrong choice
Monitoring
- CK plus bedside strength together: CK alone can mislead. Rising CK means active myositis; a normal CK with worsening weakness means the steroids, not the disease, are the problem.
- Serial PFTs q3–6 months if antisynthetase syndrome or any ILD, because ILD is the main driver of mortality and progresses quietly.
- Baseline PFTs at diagnosis in every DM patient to have a comparison before dyspnea appears.
- TPMT before azathioprine, and folic acid with methotrexate.
- Repeat malignancy screening if anti-TIF1-γ positive; some guidelines recommend annually for 3–5 years because the cancer can surface after the myositis.
Pitfalls
- Calling steroid myopathy a flare. Both cause proximal weakness. Myositis flare: CK elevated/rising, inflammatory markers up. Steroid myopathy: CK normal, painless, no inflammatory markers. If CK is normal and weakness is worsening, reduce the steroid instead of escalating it.
- Methotrexate in a patient with ILD: MTX can itself cause drug-induced ILD. Use mycophenolate, rituximab, or cyclophosphamide for antisynthetase ILD instead.
- Missing IBM. Age > 50, asymmetric weakness, distal involvement (finger flexors, wrist flexors, "can't grip"), quadriceps atrophy ("can't walk"), CK only mildly elevated or normal, and no response to immunosuppression. Biopsy shows rimmed vacuoles plus amyloid. It is the most common inflammatory myopathy in the elderly.
- Skipping cancer screening in adult DM because the muscles responded to steroids. The malignancy association is with the disease, not with treatment failure.
Malignancy Screening in DM
- DM carries the strong association, PM a weaker one. Adult DM requires age-appropriate malignancy screening at diagnosis.
- Where to look: ovarian, lung, breast, GI, lymphoma.
- Anti-TIF1-γ positive means intensify: CT chest/abdomen/pelvis, mammogram, colonoscopy, pelvic exam.
- Repeat, do not treat as a one-time box: some guidelines recommend annual screening for 3–5 years.
Escalate / Refer When
- Anti-Jo-1 positive, or new dyspnea and dry cough: get PFTs and HRCT chest. In antisynthetase syndrome the ILD, not the myopathy, is what kills.
- Refractory to prednisone plus a steroid-sparing agent: escalate to rituximab, IVIG, or mycophenolate.
- Asymmetric distal weakness that failed a 6-month steroid trial: stop escalating immunosuppression and rebiopsy for rimmed vacuoles. IBM has no effective immunosuppressive treatment; the plan becomes PT/OT and fall prevention.
- Dysphagia: formal swallowing evaluation. It is common in IBM, and IVIG may help swallowing even when it does nothing for strength.
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