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Muscle pain/myalgia

Medicine > Neurosciences

Differential Diagnosis Schema 🧠

Infectious Causes

  • Viral Myositis: Commonly caused by influenza, HIV, or other viral infections; presents with diffuse muscle aches and elevated creatine kinase (CK).
  • Bacterial Myositis: Rare, often caused by Staphylococcus aureus; presents with localized muscle pain, swelling, and erythema.
  • Parasitic Infections: Trichinosis or toxoplasmosis can lead to muscle pain, particularly in endemic areas or in immunocompromised patients.

Rheumatologic Causes

  • Polymyalgia Rheumatica: Affects older adults; presents with proximal muscle pain and stiffness, particularly in the shoulders and hips; associated with elevated inflammatory markers.
  • Fibromyalgia: Widespread musculoskeletal pain with associated fatigue, sleep disturbance, and cognitive difficulties; diagnosis of exclusion.
  • Polymyositis/Dermatomyositis: Presents with proximal muscle weakness and pain; dermatomyositis also includes characteristic skin rash.

Metabolic and Endocrine Causes

  • Hypothyroidism: Common cause of myalgia; associated with fatigue, weight gain, and cold intolerance.
  • Electrolyte Imbalances: Hypokalemia, hypocalcemia, or hypomagnesemia can cause muscle cramps and pain.
  • Statin-Induced Myopathy: Muscle pain and weakness due to statin use; associated with elevated CK levels.
  • Chronic Kidney Disease: Uremic myopathy can cause muscle pain, particularly in advanced stages of renal failure.

Neurological Causes

  • Peripheral Neuropathy: Can cause muscle pain or cramps, often associated with diabetes or chronic alcohol use.
  • Multiple Sclerosis: May present with muscle pain or spasms as part of its neurological manifestations.
  • Motor Neuron Disease: Progressive weakness and muscle wasting; may be associated with muscle pain or cramps in advanced stages.

Other Causes

  • Exercise-Induced Myalgia: Common in individuals engaging in unaccustomed physical activity; usually self-limiting.
  • Drug-Induced Myalgia: Apart from statins, other drugs like corticosteroids, antiretrovirals, or alcohol can cause muscle pain.
  • Chronic Fatigue Syndrome: Persistent, unexplained fatigue accompanied by muscle pain; diagnosis of exclusion.
  • Cancer-Related Myalgia: Paraneoplastic syndromes or direct invasion by tumor can cause muscle pain; often associated with other systemic symptoms.

Key Points in History 🥼

Symptomatology

  • Onset and Duration: Acute onset suggests infectious or traumatic causes; chronic, insidious onset may suggest a rheumatologic or metabolic condition.
  • Pain Characteristics: Diffuse versus localized pain, association with specific activities, and response to rest or exercise.
  • Associated Symptoms: Fatigue, fever, skin changes, weakness, or weight changes can help narrow the differential diagnosis.
  • Impact on Functionality: Assess how the pain affects daily activities, work, and quality of life; important for gauging severity.

Background

  • Past Medical History: Inquire about history of thyroid disease, renal disease, rheumatologic conditions, or recent infections.
  • Drug History: Review current medications, particularly statins, corticosteroids, and antiretrovirals; ask about recent changes or new prescriptions.
  • Family History: Consider family history of autoimmune diseases, metabolic conditions, or hereditary muscle disorders.
  • Social History: Assess for lifestyle factors such as exercise habits, occupational risks, alcohol use, and recent travel.
  • Recent Trauma or Surgery: Consider recent injuries, surgeries, or invasive procedures that might contribute to muscle pain.

Possible Investigations 🌡️

Laboratory Tests

  • Creatine Kinase (CK): Elevated in muscle injury, myositis, and statin-induced myopathy.
  • Inflammatory Markers: ESR and CRP may be elevated in polymyalgia rheumatica, infections, and autoimmune conditions.
  • Thyroid Function Tests: Hypothyroidism is a common cause of diffuse myalgia.
  • Electrolyte Panel: Check for abnormalities in potassium, calcium, and magnesium, which can cause muscle cramps or pain.
  • Autoantibodies: ANA, anti-dsDNA, or other specific antibodies may be indicated if autoimmune disease is suspected.
  • Rheumatoid Factor and Anti-CCP: Useful in diagnosing rheumatoid arthritis if joint symptoms are also present.
  • Serum Protein Electrophoresis: Consider if myeloma or other malignancies are suspected.

Imaging and Specialist Tests

  • Muscle Biopsy: Consider if inflammatory myopathies or muscular dystrophies are suspected; helps confirm the diagnosis.
  • MRI: Useful for identifying soft tissue abnormalities, muscle edema, or inflammation in suspected myositis or trauma.
  • Electromyography (EMG): Assess for neuromuscular disorders; can help differentiate between myopathic and neurogenic causes of muscle pain.
  • Nerve Conduction Studies: May be indicated if there is suspicion of peripheral neuropathy contributing to muscle pain.

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Neurosciences