Myalgia

Background

• Myalgia refers to muscle pain, which may be localized or diffuse
• Extremely common complaint — most cases are benign (viral illness, overexertion, medication side effect)
• Key EM concern: differentiate benign myalgia from rhabdomyolysis, myositis, and necrotizing fasciitis
• Diffuse myalgias may indicate systemic disease (viral infection, autoimmune, endocrine, toxicologic)
• Statin-induced myopathy is one of the most common medication-related causes

Clinical Features

History

• Localized vs. diffuse
• Onset: acute (trauma, overexertion, infection) vs. chronic (fibromyalgia, hypothyroidism, statin use)
• Recent exercise or immobility (rhabdomyolysis)
• Recent illness (viral myalgia)
• Medications: statins, fibrates, colchicine, zidovudine, corticosteroids (chronic)
• Drug/toxin exposure: alcohol, cocaine, amphetamines (rhabdomyolysis)
• Weakness (true weakness suggests myositis or myopathy vs. pain-limited weakness)
• Dark urine (myoglobinuria from rhabdomyolysis)
• Fever, rash, arthralgias (systemic inflammatory/infectious process)
• Weight changes, fatigue, cold intolerance (hypothyroidism)

Physical Exam

• Localized tenderness, swelling, induration
• Muscle strength testing (distinguish weakness from pain)
• Skin: rash (dermatomyositis — heliotrope rash, Gottron papules), erythema, crepitus (necrotizing fasciitis)
• Compartment assessment if concern for compartment syndrome (tense compartment, pain with passive stretch)
• Joint exam (distinguish articular from muscular pain)
• Thyroid exam

Red Flags

• Dark (tea/cola-colored) urine → rhabdomyolysis
• Severe localized pain + swelling + fever → necrotizing fasciitis or deep abscess
• Progressive proximal weakness → inflammatory myositis (dermatomyositis, polymyositis)
• Diffuse myalgias + fever + rash → consider toxic shock syndrome, viral hemorrhagic fever, vasculitis
• Pain out of proportion to exam + crepitus → necrotizing soft tissue infection

Differential Diagnosis

Myalgia

• Infection:
  • Viral infection (e.g. Influenza)
  • Bacterial infection
  • Spirochete infection (E.g. Dengue fever; Trichinella)
• Drugs:
  • Statins
  • Bisphosphonates
  • Corticosteroids
  • Ciprofloxacin
  • Clofibrate
  • Colchicine
  • Chloroquine
  • Emetine
  • Aminocaproic acid
  • Zidovudine
  • Bretylium
  • Penicillamine
  • Drugs causing hypokalemia
• Metabolic disorders:
  • Vitamin D deficiency
  • Mitochondrial myopathy
  • Scurvy
  • Osteomalacia
• Fibromyalgia
• Endocrine:
  • Hypothyroidism
  • Hyperthyroidism
  • Cushing’s syndrome
  • Adrenal insufficiency
  • Hyperparathyroidism
• Polymyalgia rheumatica
• Rhabdomyolysis
• Myositis
  • Polymyositis
  • Dermatomyositis
  • Myositis (peds)
• Systemic lupus erythematosus
• Rheumatoid arthritis
• Inclusion body myositis
• Sarcoidosis
• Scleroderma
• Sjögren’s syndrome
• Psychiatric (e.g. somatic manifestations of depression)
• Domestic abuse
• Crush injury
• Lyme disease
• Ehlers-Danlos syndrome(hypermobility syndrome)
• HIV myopathy
• Hypophosphatemia
• Hypokalemia
• Hypothermia
• Prolonged immobility
• Strenuous exercise (overuse) or heat stroke
• Seizure
• Severe volume contraction
• Alcoholism
• Muscular dystrophy
  • Duchenne
  • Becker
  • Limb-girdle
  • Facioscapulohumeral
  • Myotonic dystrophy
  • Myotonia congenita
• Compartment syndrome; Muscle infarction
• Neuropathic
• Chronic fatigue syndrome
• Vasculitis
• Sarcocystosis
• Spinal stenosis
• Diabetic lumbosacral plexopathy

Localized

• Muscle strain/overuse
• Contusion
• Compartment syndrome
• Necrotizing fasciitis
• Abscess/pyomyositis
• Stress fracture

Diffuse

• Viral illness (influenza, COVID-19, EBV, dengue, enterovirus — most common cause)
• Rhabdomyolysis (exertional, traumatic, drug-induced)
• Medication-induced: statins, fibrates, ACE inhibitors, colchicine
• Inflammatory myopathy: dermatomyositis, polymyositis, inclusion body myositis
• Endocrine: hypothyroidism, adrenal insufficiency, vitamin D deficiency
• Electrolyte abnormality: hypokalemia, hypocalcemia, hypomagnesemia, hypophosphatemia
• Autoimmune/rheumatologic: SLE, polymyalgia rheumatica, vasculitis
• Toxicologic: alcohol, cocaine, serotonin syndrome, neuroleptic malignant syndrome
• Fibromyalgia (diagnosis of exclusion)

Evaluation

When Workup is Needed

• Diffuse myalgias with red flags (dark urine, weakness, fever)
• Localized myalgias with signs of infection or compartment syndrome
• Mild myalgias from viral illness or overexertion typically need no workup

Laboratory

• CK (creatine kinase): key test — markedly elevated in rhabdomyolysis (>5x normal), moderately elevated in myositis
• BMP: renal function (rhabdomyolysis can cause AKI), potassium, calcium, phosphate
• Urinalysis: positive for blood on dipstick with no RBCs on microscopy = myoglobinuria
• CBC: infection, leukemia
• TSH if chronic or unexplained myalgias
• LFTs, aldolase if inflammatory myopathy suspected
• ESR/CRP if inflammatory process suspected
• Toxicology screen if drug-related rhabdomyolysis suspected

Imaging

• Not routinely needed for diffuse myalgia
• CT or MRI if abscess, deep space infection, or compartment syndrome suspected
• X-ray if stress fracture or bony pathology considered

Management

General

• Analgesics: NSAIDs, acetaminophen
• Rest, ice for localized strains
• Discontinue offending medication if drug-induced (statins — discuss with PCP)

Rhabdomyolysis

• Aggressive IV fluid resuscitation (NS at 200-300 mL/hr initially)
• Monitor CK, electrolytes, renal function serially
• Correct electrolyte abnormalities (especially hyperkalemia, hypocalcemia)
• See Rhabdomyolysis for detailed management

Myositis/Inflammatory

• Rheumatology consultation
• May require corticosteroids or immunosuppressive therapy

Disposition

Admit

• Rhabdomyolysis with CK >5,000 or renal impairment
• Necrotizing fasciitis or deep space infection
• Compartment syndrome
• Severe electrolyte derangements
• Inflammatory myopathy with respiratory muscle weakness

Discharge

• Viral myalgias with normal labs
• Mild statin myopathy (coordinate medication change with PCP)
• Muscle strain with pain control
• Return precautions: dark urine, severe worsening pain, weakness, fever, decreased urine output

See Also

• Rhabdomyolysis
• Compartment syndrome
• Polymyalgia rheumatica
• Monoarticular arthritis