What is the difference between myalgia and myopathy?

Myalgia versus Myopathy: Comparison

Myalgia and myopathy are distinct muscle conditions with different pathophysiological mechanisms, clinical presentations, and management approaches, with myalgia referring to muscle pain without structural damage while myopathy involves actual muscle tissue damage with potential weakness.

Comparison Table

Feature	Myalgia	Myopathy
Definition	Muscle pain or aches without objective weakness or tissue damage [1]	Disease of muscles with structural or functional impairment [1]
Pathophysiology	Pain sensation without actual muscle damage	Actual damage to muscle tissue (inflammation, degeneration, etc.)
Creatine Kinase (CK) Levels	Normal	Elevated (often >ULN) [1]
Muscle Strength	Preserved	Often reduced (proximal > distal) [1]
Clinical Presentation	Pain, tenderness, discomfort without weakness	Weakness (often proximal), possible pain, functional impairment [1]
EMG Findings	Normal	Abnormal - polyphasic motor unit potentials of short duration and low amplitude [1]
Muscle Biopsy	Normal	Abnormal - specific findings based on type of myopathy [1]
Duration	Often transient	May be chronic or progressive
Examples	Statin-associated myalgia, viral myalgia, fibromyalgia	Inflammatory myopathies (dermatomyositis, polymyositis), toxic myopathies, metabolic myopathies [1]
Treatment Approach	Symptomatic relief, address underlying cause	Treat underlying disease, immunosuppression for inflammatory causes [2]
Prognosis	Usually good with resolution after addressing cause	Variable depending on type and severity

Key Distinguishing Features

Myalgia

• Characterized by muscle pain without objective weakness 1
• Normal muscle enzyme levels (CK, aldolase) 1
• No structural damage to muscle fibers
• Normal EMG and muscle biopsy findings
• Often resolves with removal of triggering factors 3

Myopathy

• Involves actual muscle damage with potential weakness 1
• Elevated muscle enzymes (CK often >ULN) 1
• May include inflammatory infiltrates (myositis), necrosis, or other structural changes 1
• Abnormal EMG findings with myopathic pattern 1
• May require specific treatment based on underlying cause 2

Clinical Relevance

Diagnostic Approach

• Distinguish between simple myalgia and true myopathy to guide appropriate management
• For suspected myopathy, perform:
  • Muscle enzyme tests (CK, aldolase, transaminases)
  • EMG to confirm myopathic process
  • MRI of affected muscles
  • Muscle biopsy in selected cases 1, 2

Common Causes

• Statin therapy can cause both myalgia (more common, 1-5% in RCTs) and myopathy (rare) 1
• Inflammatory conditions like dermatomyositis can cause myopathy 1
• Drug-induced cases may present as either myalgia or myopathy 3

Management Implications

• Myalgia: Often managed with symptomatic treatment and addressing underlying cause
• Myopathy: May require specific therapies (e.g., immunosuppression for inflammatory myopathies, drug discontinuation for toxic myopathies) 2, 3

Pitfalls and Caveats

• Myalgia may be an early symptom of developing myopathy - monitor for progression 3
• Some conditions can present with both (e.g., statin-associated muscle symptoms) 1
• Drug-drug interactions can increase risk of progression from myalgia to myopathy 3
• Certain drugs like statins require monitoring for progression from myalgia to myopathy 1
• Inflammatory myopathies may have extramuscular manifestations that aid diagnosis 1