Should I Order This Test?

Should I Order a
Myositis Panel?

Primary care screening tool for idiopathic inflammatory myopathies. Use when evaluating unexplained muscle weakness, elevated CK, or systemic autoimmune features suggesting dermatomyositis or polymyositis.

📋 Adapted from EULAR/ACR IIM Classification Criteria · Includes CK Elevation Interpreter
Clinical decision support only. This tool is intended to assist clinicians in identifying patients who may warrant further evaluation for inflammatory myopathies. It does not establish a diagnosis and should not replace clinical judgment. Myositis is a rare disease — clinical context and specialist input are essential before initiating treatment.
1
Muscle Symptoms
Objective or convincing muscle weakness — distinguish from fibromyalgia or fatigue-related weakness
Progressive proximal muscle weakness
Difficulty climbing stairs, rising from chair without using arms, or getting up from floor
+3
Difficulty lifting arms above shoulders
Shoulder girdle weakness — unable to lift arms to wash/comb hair or reach overhead shelves
+2
Dysphagia or choking on food / liquids
Pharyngeal or esophageal involvement — symptom of pharyngeal muscle weakness in PM/DM; aspiration risk
+2
Neck flexor weakness
Patient cannot lift head from pillow; chin-to-chest maneuver — characteristic of PM/DM, IBM
+1
Muscle pain accompanied by weakness
Myalgias alone are non-specific; significant when occurring alongside objective weakness
+1
IBM pearl: Inclusion body myositis (IBM) — the most common inflammatory myopathy over age 50 — classically involves asymmetric distal + proximal weakness, especially finger flexors and knee extensors. Consider IBM if weakness is slowly progressive and asymmetric.
2
Skin Findings — Dermatomyositis
Pathognomonic cutaneous features of DM — presence of any of these significantly raises pre-test probability
Gottron's papules
Scaly, erythematous papules over the dorsal MCPs and PIPs — pathognomonic for dermatomyositis
+3
Heliotrope rash
Violaceous (purple-lilac) discoloration of eyelids, sometimes with periorbital edema — pathognomonic for DM
+3
Mechanic's hands
Hyperkeratosis, cracking, and fissuring of lateral fingers and palmar surface — strongly associated with anti-Jo-1 and antisynthetase syndrome
+2
Shawl sign or V-sign rash
Photodistributed erythema across upper back/shoulders (shawl) or anterior chest (V-sign)
+1
Amyopathic dermatomyositis (CADM): Up to 20% of DM patients have skin findings with little or no muscle weakness. Anti-MDA5 is strongly associated with CADM and rapidly progressive ILD — do not dismiss pathognomonic skin findings even without elevated CK.
3
Laboratory Findings
Muscle enzyme elevations — objective markers of myocyte injury
CK elevated >2× upper limit of normal
Most sensitive lab in PM/DM; CK can be normal in IBM and DM (especially amyopathic) — use the CK tool on this page
+3
AST/ALT elevated without liver disease
Transaminases are also muscle-derived — "hepatitis" in myositis is frequently misdiagnosed; check GGT/ALP to differentiate hepatic from muscle source
+1
Aldolase elevated
Less specific than CK but may be elevated when CK is normal in DM — useful when CK is unexpectedly low
+1
LDH elevated
Non-specific; supports muscle/tissue injury pattern when elevated alongside other enzyme elevations
+1
4
Systemic Features
Extramuscular involvement — raises overall suspicion and guides urgency of referral
Interstitial lung disease (ILD)
Dyspnea, reduced DLCO, or ILD on chest CT — present in ~40% of IIM; anti-Jo-1 and anti-MDA5 most associated
+2
Raynaud's phenomenon
Triphasic color changes of digits — associated with antisynthetase syndrome and overlap myositis
+1
Inflammatory arthritis
Non-erosive joint inflammation — common in antisynthetase syndrome; helps distinguish from IBM
+1
Unexplained fever
Systemic inflammation — more common in anti-MDA5+ CADM and aggressive DM
+1
Age >40 with new DM features
DM has strong paraneoplastic association — malignancy screen is indicated in all adult-onset DM (anti-TIF1-γ most strongly linked)
+1
ILD urgency: Anti-MDA5 is associated with rapidly progressive ILD — mortality up to 50% in some series without prompt immunosuppression. If ILD is suspected in a patient with DM features, this warrants urgent rheumatology and pulmonology evaluation, not a routine referral.
−
Alternative Explanations
Points are subtracted when alternative causes of CK elevation or muscle symptoms are present
Active statin use
Most common cause of CK elevation in primary care — hold statin and recheck CK in 4–6 weeks; note IMNM is a rare statin-triggered autoimmune myopathy (anti-HMGCR)
−2
Known or suspected hypothyroidism
Hypothyroidism causes proximal myopathy AND elevated CK — check TSH before ordering myositis panel; treat first and recheck
−2
Recent strenuous exercise (<72 hours)
Exercise-induced rhabdomyolysis — CK peaks 24–72 hrs post-exercise; recheck after 5+ days of rest
−1
Electrolyte abnormalities
Hypokalemia, hypomagnesemia, and hypophosphatemia can all cause muscle weakness and elevated CK
−1
IMNM exception: If statin use is present but the clinical picture is severe (very high CK, rapid progression, no improvement after stopping statin) — consider immune-mediated necrotizing myopathy (anti-HMGCR antibody). This is a statin-triggered autoimmune myopathy that does NOT resolve with statin cessation.
📋
Myositis Antibody Panel — What's Included?
Myositis-specific antibodies (MSA) and myositis-associated antibodies (MAA) — each predicts distinct clinical phenotypes
Antisynthetase
Anti-Jo-1
Most common MSA. Antisynthetase syndrome: PM + ILD + mechanic's hands + Raynaud's + arthritis. Predicts ILD strongly.
DM-specific
Anti-Mi-2
Classic DM with florid skin features. Low ILD risk. Good treatment response. Paraneoplastic association lower than TIF1-γ.
IMNM
Anti-SRP
Immune-mediated necrotizing myopathy. Severe muscle weakness, very high CK, poor treatment response. Not statin-triggered.
IMNM · Statin
Anti-HMGCR
Statin-triggered IMNM. Does NOT improve with statin cessation — requires immunosuppression. Critical to distinguish from statin myopathy.
DM · Cancer
Anti-TIF1-γ
Most strongly associated with cancer-associated DM in adults. Prompt age-appropriate malignancy screen indicated. Amyopathic DM common.
DM · Rapid ILD
Anti-MDA5
Amyopathic DM with rapidly progressive ILD. High mortality without urgent treatment. Skin ulcers and palmar papules common.
Antisynthetase
Anti-PL-7 / Anti-PL-12
Antisynthetase syndrome variants. Prominent ILD, often with less muscle involvement than anti-Jo-1.
Juvenile DM
Anti-NXP2
Commonest MSA in juvenile DM. Associated with calcinosis and edema. In adults, paraneoplastic association present.
Clinical decision support only. CK elevation has a broad differential. This tool helps stratify concern and guides the diagnostic workup — it does not establish a diagnosis. Always consider the full clinical picture including medication history, exercise, and muscle symptoms.
Enter the patient's CK result
ULN: 200 U/L (male) · Enter CK result below
U/L
Reference ranges: Male 39–308 U/L · Female 26–192 U/L (lab-specific; use your lab's ULN)
i
CK Elevation — Quick Reference
Degree of elevation guides the differential — most inflammatory myopathies present with CK >10× ULN
Level Fold × ULN Common Causes
Mild 1–3× Exercise, statins, hypothyroidism, alcohol, African American race (higher baseline), DM (amyopathic)
Moderate 3–10× Statin myopathy, inflammatory myositis, viral myositis, hypothyroid myopathy, muscular dystrophy
High 10–50× PM/DM, IMNM, muscular dystrophy, rhabdomyolysis, crush injury, cocaine or alcohol myopathy
Very High >50× Rhabdomyolysis — acute renal failure risk; trauma, crush, seizure, drug toxicity, IMNM (anti-SRP)
Race/ethnicity note: CK values are physiologically higher in individuals of African descent — mean CK may be 1.5–2× higher than published reference ranges. Adjust interpretation accordingly and avoid over-investigation of mild elevations in asymptomatic patients.

Frequently Asked Questions

Common questions clinicians and patients ask after using this tool — and after receiving these results.

What is inflammatory myositis and how common is it? ▼
Inflammatory myositis (idiopathic inflammatory myopathy / IIM) is a group of autoimmune conditions that cause muscle inflammation, leading to weakness, elevated muscle enzymes, and — in dermatomyositis — characteristic skin findings. The main subtypes are dermatomyositis (DM), polymyositis (PM), immune-mediated necrotizing myopathy (IMNM), and inclusion body myositis (IBM). IIM is rare, affecting approximately 1 in 100,000 people. Despite this, it is important not to miss — untreated inflammatory myositis can cause progressive disability, aspiration pneumonia, interstitial lung disease, and in DM, is associated with underlying malignancy in adults.
What is the difference between dermatomyositis and polymyositis? ▼
Both are inflammatory myopathies, but dermatomyositis has pathognomonic skin findings that distinguish it from polymyositis: Gottron's papules (scaly red-purple plaques over the knuckles) and heliotrope rash (violaceous discoloration around the eyelids). PM lacks these features and is increasingly recognized as a diagnosis of exclusion. Amyopathic dermatomyositis (CADM) is a DM variant with skin findings but minimal or no muscle involvement — CK can be normal. Anti-MDA5 antibody in CADM is associated with rapidly progressive interstitial lung disease, which can be fatal without prompt treatment.
What is inclusion body myositis (IBM)? ▼
IBM is the most common inflammatory myopathy in patients over 50, but it is frequently misdiagnosed as polymyositis or statin myopathy. Key distinguishing features of IBM: insidious onset over years (not months), asymmetric weakness (unusual for PM/DM), prominent involvement of finger flexors (can't grip) and knee extensors (difficulty climbing stairs), dysphagia from pharyngeal muscle involvement, and relatively modest CK elevation. IBM responds poorly to immunosuppressive therapy — unlike PM and DM — which makes accurate diagnosis critical before initiating treatment. IBM requires neuromuscular specialist evaluation and muscle biopsy for confirmation.
Which myositis antibody is associated with lung disease? ▼
Several myositis-specific antibodies (MSAs) are associated with interstitial lung disease (ILD), but anti-MDA5 carries the highest risk of rapidly progressive ILD with mortality rates up to 30–50% without prompt treatment. Other ILD-associated antibodies include the antisynthetase antibodies: anti-Jo-1 (most common, ~80% ILD risk), anti-PL-7, anti-PL-12, anti-EJ, and anti-OJ. These form the antisynthetase syndrome: myositis + ILD + mechanic's hands + Raynaud's + arthritis. Any myositis patient with dyspnea or reduced exercise tolerance requires chest CT and pulmonary function testing with DLCO.
What is the connection between dermatomyositis and cancer? ▼
Dermatomyositis has a well-established association with malignancy — approximately 15–25% of adult-onset DM is paraneoplastic. The risk is highest in the first 1–3 years after DM diagnosis. Common associated cancers include ovarian, lung, colorectal, breast, and nasopharyngeal carcinoma. Anti-TIF1-γ antibody is most strongly associated with cancer-associated DM and should prompt thorough malignancy screening. All adults newly diagnosed with dermatomyositis should undergo age-appropriate cancer screening (CT chest/abdomen/pelvis, gynecologic evaluation, colorectal screening). The skin findings can precede or follow cancer diagnosis.
Why might the CK be normal in dermatomyositis? ▼
Up to 20% of dermatomyositis patients have a normal or near-normal CK, particularly in amyopathic dermatomyositis (CADM) where muscle involvement is minimal. This is because the primary pathology in DM is a complement-mediated microangiopathy affecting blood vessels rather than direct muscle fiber destruction — the mechanism differs from polymyositis. A normal CK does not exclude dermatomyositis. If pathognomonic skin findings (Gottron's papules or heliotrope rash) are present, refer to rheumatology regardless of CK level. Aldolase may be elevated when CK is not, making it a useful complementary test.
References
  1. Lundberg IE, et al. 2017 European League Against Rheumatism/American College of Rheumatology classification criteria for adult and juvenile idiopathic inflammatory myopathies. Ann Rheum Dis. 2017;76(12):1955–1964.
  2. Rider LG, et al. Update on outcome assessment in myositis. Nat Rev Rheumatol. 2018;14(5):303–318.
  3. Allenbach Y, et al. 224th ENMC International Workshop: Clinico-sero-pathological classification of immune-mediated necrotizing myopathies. Neuromuscul Disord. 2018;28(1):87–99.
  4. Connors GR, et al. Interstitial lung disease associated with the idiopathic inflammatory myopathies. Chest. 2010;138(6):1464–1474.
  5. Fiorentino D, et al. Most patients with cancer-associated dermatomyositis have antibodies to nuclear matrix protein NXP-2 or transcription intermediary factor 1γ. Arthritis Rheum. 2013;65(11):2954–2962.
  6. Pinal-Fernandez I, et al. Anti-MDA5 autoantibody-associated interstitial lung disease in dermatomyositis: clinical characteristics, treatment response, and outcomes. Arthritis Care Res. 2020;72(2):267–272.