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Inflammatory Myositis Muscle Strength

MMT-8
Manual Muscle Testing - 8 Muscle Groups

Standardized manual muscle testing of 8 bilateral proximal, distal, and axial muscle groups using the validated IMACS 0–10 grading scale. Maximum 80 points. The objective muscle strength component of the IMACS core outcome set. Required for the 2016 ACR/EULAR myositis response criteria (minimal, moderate, and major improvement thresholds).

Original Development
Rider LG, Giannini EH, Harris-Love M, et al. (IMACS)
Arthritis Care Res, 2003 & Miller et al. 2001
Important: The MMT-8 assesses 8 muscle groups on the dominant side only per the IMACS protocol (with the exception of neck flexors and hip flexors, which are tested bilaterally in some protocols). Use the standardized IMACS grading scale (0–10) below, not the traditional MRC 0–5 scale.
Grading Scale (IMACS 0–10)
10
Normal (10) - Active movement against gravity with full resistance. No palpable lag or give-way.
9
Near normal (9) - Active movement against gravity with nearly full resistance. Slight weakness.
8
Good (8) - Active movement against gravity with moderate resistance. Mild weakness.
7
Good- (7) - Active movement against gravity with some resistance.
6
Fair+ (6) - Active movement against gravity with slight resistance.
5
Fair (5) - Active movement against gravity only, no resistance.
4
Poor+ (4) - Active movement with gravity eliminated and moderate resistance.
3
Poor (3) - Active movement with gravity eliminated.
2
Trace (2) - Visible or palpable contraction, no movement.
1
Zero with test (1) - No palpable contraction; patient states aware of deficit.
0
Zero (0) - No contraction, no awareness. Complete paralysis.
Rate Each Muscle Group (Dominant Side)
Muscle Group Test Grade (0–10)
📋 About MMT-8

The MMT-8 was developed by the International Myositis Assessment and Clinical Studies (IMACS) group to provide a standardized, reproducible measure of muscle strength in inflammatory myopathy. It tests 8 muscle groups that are representative of the proximal, distal, and axial muscles affected in IIM: deltoid, biceps, wrist extensors, quadriceps, hip flexors, ankle dorsiflexors, neck flexors, and hip abductors.

The MMT-8 is one of the six core set measures in the IMACS outcome set for IIM, alongside physician global disease activity (MDGA), patient global disease activity (PDGA), functional ability (HAQ-DI), laboratory enzymes (CK, aldolase, LDH, AST, ALT), and global extramuscular disease activity. The 2016 ACR/EULAR myositis response criteria (IMACS) require all six measures for the response calculation.

📊 Interpreting the Score

The MMT-8 maximum is 80 (10 per muscle × 8 muscles). In active inflammatory myositis, MMT-8 scores are typically 40–70 at baseline in clinical trials. Response thresholds from the 2016 ACR/EULAR criteria:

IMACS Response Criteria (ACR/EULAR 2016)
Minimal improvement: ≥ 20% improvement in 3 of 6 core measures (≤2 worsening by >25%)
Moderate improvement: ≥ 20% improvement in 3 of 6 core measures (≤2 worsening by >25%), with at least one being MMT-8 or physician global
Major improvement: ≥ 40% improvement in 3 of 6 core measures
💡 Pearls and Pitfalls
✓
Use the IMACS 0–10 scale, not MRC 0–5. The MMT-8 uses a 0–10 scale that subdivides the traditional MRC scale. Using MRC grades and multiplying by 2 produces a similar number but not an equivalent score - the two scales weight moderate weakness differently. Standardization with the IMACS protocol is required for valid scoring.
✓
MMT-8 must be combined with the other 5 IMACS core measures for response criteria. The MMT-8 alone does not define treatment response. The 2016 ACR/EULAR criteria require all 6 core outcome measures (MMT-8, MDGA, PDGA, HAQ-DI, enzyme, extramuscular activity) to calculate minimal, moderate, or major improvement.
⚠
Inclusion body myositis (IBM) has a distinct muscle testing pattern. In IBM, finger flexors and quadriceps are disproportionately affected - a pattern that differs from PM/DM (which shows proximal > distal). Consider testing the IBM-specific pattern alongside the standard MMT-8 in patients with clinical features of IBM.
🔬 Evidence

The MMT-8 and its grading scale were developed and standardized by the IMACS group, published by Miller and colleagues in 2001, and subsequently refined by Rider and colleagues in 2003. The 0–10 grading system provides greater sensitivity to change than the traditional MRC scale, particularly in the 4–8 range where most clinical change in treated myositis patients occurs.

View References▾
1
Miller FW, Rider LG, Chung YL, et al. Proposed preliminary core set measures for disease outcome assessment in adult and juvenile idiopathic inflammatory myopathies. Rheumatology. 2001;40(11):1262-1273.
2
Rider LG, Giannini EH, Brunner HI, et al. International consensus on preliminary definitions of improvement in adult and juvenile myositis. Arthritis Rheum. 2004;50(7):2281-2290.
3
Aggarwal R, Rider LG, Ruperto N, et al. 2016 American College of Rheumatology/European League Against Rheumatism criteria for minimal, moderate, and major clinical response in adult dermatomyositis and polymyositis. Ann Rheum Dis. 2017;76(5):792-801.
For clinical decision support only. MMT-8 requires physical examination by a trained clinician using the standardized IMACS protocol. Scores should be interpreted in the context of all 6 IMACS core outcome measures. The MMT-8 alone does not define myositis response or remission.
🔗 Related Calculators
🩺
MDGA / PDGA
Physician and patient global disease activity VAS
→ 💪
2017 EULAR/ACR Myositis Classification
Classification criteria for IIM subtypes
→ 🦽
HAQ-DI
Functional disability - also part of IMACS core set
→
MMT-8 Total
80
/ 80
040607280
Normal Strength
Clinical Interpretation
Grade each of the 8 muscle groups above using the IMACS 0–10 scale.
Reviewed by Mahiar Rabie, MS, MD · AutoimmuneCalc