Muscle Pain Myalgia

💪 Muscle pain (myalgia) is a common symptom with a wide differential - ranging from benign self-limiting causes to medical emergencies. The clinical task is to distinguish mechanical or viral pain from inflammatory, metabolic, or toxic muscle injury, and to recognise red flags that mandate urgent investigation.

🚨 High-Risk Causes of Muscle Pain

• Rhabdomyolysis 💥 A medical emergency caused by skeletal muscle breakdown with release of myoglobin → acute kidney injury. Key features: Severe muscle pain and swelling, proximal weakness, dark “cola-coloured” urine, reduced urine output. Triggers: Trauma, prolonged immobilisation, extreme exercise, statins, alcohol, illicit drugs, seizures. Action: Immediate admission, aggressive IV fluids, CK monitoring, U&E (especially K⁺), treat precipitant.
• Inflammatory Myositis 🔬 (e.g. polymyositis, dermatomyositis) Immune-mediated muscle inflammation causing weakness ± pain. Key features: Proximal weakness (difficulty climbing stairs, rising from chair), myalgia, raised CK; rash in dermatomyositis. Action: CK, autoantibodies, EMG, MRI, ± muscle biopsy. Treat with corticosteroids ± immunosuppressants.
• Polymyalgia Rheumatica (PMR) ⏳ Inflammatory condition in adults >50 years causing stiffness rather than true weakness. Key features: Bilateral shoulder and hip girdle pain, morning stiffness >45 minutes, raised ESR/CRP. Critical association: Giant cell arteritis → risk of sudden irreversible blindness. Action: Prompt oral steroids, inflammatory marker monitoring, urgent escalation if visual symptoms.

📋 Other Common Causes of Myalgia

• Muscle Strain / Overuse 🏋️ Localised pain after exertion or trauma.
  Management: Rest, ice, simple analgesia, graded return to activity.
• Fibromyalgia 🌐 Central pain sensitisation syndrome.
  Key features: Widespread pain, fatigue, poor sleep, cognitive “fog”. CK normal.
  Management: Education, exercise, sleep optimisation, CBT ± neuromodulators.
• Infection-Related Myalgia 🦠 Common with viral illness (influenza, COVID-19, EBV).
  Key features: Diffuse muscle pain with fever and systemic symptoms.
  Management: Supportive; investigate if severe or prolonged.
• Medication-Induced Myopathy 💊 Most commonly statins, corticosteroids, antiretrovirals.
  Key features: Symmetrical proximal pain ± weakness; CK may be normal or raised.
  Management: Stop or switch drug; monitor CK.
• Systemic Autoimmune Disease 🧬 (e.g. SLE, vasculitis, sarcoidosis).
  Key features: Myalgia with rash, arthritis, fatigue, organ involvement.
  Management: Autoimmune screen and specialist referral.

🩺 Clinical Assessment – A Practical Approach

• 🔍 History:
  • Onset (acute vs chronic), distribution (focal vs generalised)
  • Weakness vs pain vs stiffness
  • Recent exercise, trauma, infection
  • Drug history (statins, steroids)
• 🧪 Investigations:
  • CK (key discriminator)
  • U&E, LFTs, CRP/ESR
  • Urine dip (blood with no RBCs → myoglobin)
  • Autoimmune screen if inflammatory features
• ⚖️ Risk Factors:
  • Statins, alcohol, illicit drugs
  • Autoimmune disease
  • Recent viral illness

🚨 Red Flags – Do Not Miss

• 🩸 Dark urine or oliguria
• 💪 Rapidly progressive weakness
• 🌡️ Fever with severe myalgia
• 🧠 Visual symptoms or jaw claudication (PMR/GCA)
• 📈 Markedly raised CK

💡 Teaching Pearls

• Pain ≠ weakness - always clarify which the patient means. • Rhabdomyolysis = pain + weakness + dark urine until proven otherwise. • PMR causes stiffness, not true weakness - and think GCA. • Normal CK makes inflammatory myopathy unlikely. • Myalgia is common, but red flags demand urgent action.