Inflammatory myopathy

Inflammatory Myopathy
Home
Overview
Classification
Differentiating Inflammatory myopathy from other Diseases

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Sadaf Sharfaei M.D.[2]

Classification

• The 2017 European League Against Rheumatism and American College of Rheumatology (EULAR/ACR) classified idiopathic inflammatory myopathy into 6 subtypes:
  • Polymyositis
  • Dermatomyositis
  • Inclusion body myositis
  • Immune−mediated necrotizing myopathies (IMNM)
  • Amyopathic dermatomyositis
  • Juvenile dermatomyositis

The 2017 EULAR/ACR classification criteria for adult and juvenile idiopathic inflammatory myopathy	Score
Variable	No muscle biopsy	With muscle biopsy
Age of onset ≥ 18 and < 40 years	1.3	1.5
Age of onset ≥ 40 years	2.1	2.2
Objective symmetric weakness, usually progressive, of the proximal upper extremities	0.7	0.7
Objective symmetric weakness, usually progressive, of the proximal lower extremities	0.8	0.5
Neck flexors are relatively weaker than neck extensors	1.9	1.6
In the legs, proximal muscles are relatively weaker than distal muscles	0.9	1.2
Heliotrope rash	3.1	3.2
Gottron’s papules	2.1	2.7
Gottron’s sign	3.3	3.7
Dysphagia or esophageal dysmotility	0.7	0.6
Anti−Jo1 autoantibody present	3.9	3.8
Elevated serum levels of CK or LDH* or ASAT/AST/SGOT* or ALAT/ALT/SGPT*	1.3	1.4
Endomysial infiltration of mononuclear cells surrounding, but not invading, myofibers on muscle biopsy		1.7
Perifascicular atrophy		1.9
Rimmed vacuoles		3.1

Probability of IIM including muscle biopsy=1/[1+exponential (5.33–score)]

Probability of IIM without muscle biopsy=1/[1+exponential (6.49–score)]

To use the calculator to assess the probability of IIM, click here.

Classification algorithm for subgroups of IIM

Abbreviation: ACR, American College of Rheumatology; EULAR, European League Against Rheumatism; IIM, idiopathic inflammatory myopathies;

A patient meets the EULAR/ACR classification criteria for IIM (probability of IIM ≥55%)

Age of onset 0-17 years old

No

Yes

Skin manifestations include Heliotrope rash, Gottron's papules, or Gottron's sign

Skin manifestations include Heliotrope rash, Gottron's papules, or Gottron's sign

No

Yes

No

Yes

Clinical features include finger flexor weakness, or no treatment response, or Muscle biopsy includes rimmed vacuoles

Muscle weakness manifested as objective progressive symmetric muscle weakness of proximal upper or lower extremities, neck flexors relatively weaker than extensors, or in the legs proximal muscles relatively weaker than distal

Juvenile myositis other than juvenile dermatomyositis

Juvenile dermatomyositis

No

Yes

No

Yes

Polymyositis, or immune-mediated necrotizing myopathy

Inclusion body myositis

Amyopathic dermatomyositis

Dermatomyositis

Differentiating Inflammatory Myopathy from other Diseases

Organ system	Disease	Age of onset	Muscle weakness	Fever	Myalgia	Contractures	Gait abnormality	Neuropathy	Atrophy	Stiffness	Myoglobinuria	Other features	History	Physical Examination	Laboratory Findings	Creatine Kinase	Muscle Biopsy	Electromyogram
Inflammatory/ Rheumatologic	Dermatomyositis	40s−50s Can affect children	Proximal	+	+	−	−	−	−	+	−	Rash Dyspnea Weight loss Cough	Viral infections Cancer	Heliotrope rash on face and hands Telangiectasia Erythema Mechanic's hands Gottron's sign ( violaceous scaly eruption )	↑↑ ESR ↑↑ CRP	↑↑	Perimysial mononuclear infiltrate	Myopathic
	Polymyositis	> 18 years	Proximal	+	+	−	−	−	−	+	−	Similar to dermatomyositis without mucous and skin involvement	N/A	N/A	↑↑ ESR ↑↑ CRP	↑↑	Endomysial mononuclear infiltrate Patchy necrosis
	Inclusion body myositis	50s	Proximal & distal	−	−	−	−	−	−	−	−	Dysphagia Asymmetric weakness	Retrovirus (most common)	N/A	Antibodies to cytoplasmic 5'−nucleotidase	↑↑	Inflammatory cells Invading muscle cells Vacuolar degeneration Inclusions or plaques	Neurogenic
	Immune−mediated necrotizing myopathies (IMNM)	30s−70s	Proximal	−	−	−	−	−	−	−	−	Severe symmetric weakness Interstitial lung disease Cardiac involvement	Statin use Viral infections (HIV or hepatitis C)	N/A	Anti−SRP and anti−HMGCoAR autoantibodies	↑↑↑	Minimal or no inflammatory infiltrates and marked muscle necrosis	Myopathic
	Amyopathic dermatomyositis	40s−60s	−	−	−	−	−	−	−	−	−	Rash Pruritus Photosensitivity	N/A	Heliotrope rash on face and hands Gottron's sign ( violaceous scaly eruption )	Normal	Normal	Normal	Normal
	Fibromyalgia	40−50s	Generalized	−	−	−	−	+	−	−	−	Anxiety or depression features Fatigue Sleep disturbance Numbness Muscle spasms	History of depression	Tenderness in the soft tissue anatomical location	Normal	Normal	Normal	Normal
	Polymyalgia Rheumatica	50s	Diffuse	+	+	−	−	−	−	+	−	Weight loss	History of joints stiffness, worse in the morning	Restricted shoulder motion	↑↑ ESR ↑↑ CRP	Normal	Normal	Normal
Organ system	Disease	Age of onset	Muscle weakness	Fever	Myalgia	Contractures	Gait abnormality	Neuropathy	Atrophy	Stiffness	Myoglobinuria	Other features	History	Physical Examination	Laboratory Findings	Creatine Kinase	Muscle Biopsy	Electromyogram