What are the differential diagnoses and management options for left arm pain?

Left Arm Pain: Differential Diagnoses and Management

Immediate Life-Threatening Conditions to Rule Out First

The most critical priority when evaluating left arm pain is to immediately exclude acute coronary syndrome (ACS), as this represents the highest mortality risk and requires ECG within 10 minutes and immediate troponin measurement. 1, 2

Cardiac Causes (Highest Priority)

• Acute Coronary Syndrome is the most urgent consideration when left arm pain is present, particularly if accompanied by chest discomfort 1, 2

  • ST-elevation myocardial infarction (STEMI): persistent chest pain >20 minutes with ST elevation on ECG 2
  • Non-ST elevation myocardial infarction (NSTEMI): typical chest pain with elevated troponin but no persistent ST elevation 2
  • Unstable angina: ischemic pain at rest or with minimal exertion without myocardial necrosis 2
  • Classic presentation includes substernal pressure radiating to left arm, though right arm involvement occurs twice as frequently in actual MI patients compared to non-cardiac chest pain 1, 3
  • Diaphoresis has 95% specificity (LR 5.18) for ACS 1, 2

• Aortic Dissection must be considered with sudden, tearing pain radiating to the back, especially with hypertension history, bicuspid aortic valve, or Marfan syndrome 2

  • Requires immediate blood pressure control with beta-blockers (IV propranolol, metoprolol, esmolol, or labetalol) to reduce systolic BP to 100-120 mmHg 4
  • Pain relief with morphine sulfate is essential 4

• Acute Pericarditis presents with sharp, pleuritic chest pain that worsens supine and improves sitting forward, potentially radiating to the arm 2

Non-Cardiac Life-Threatening Causes

• Pulmonary Embolism causes pleuritic chest pain with dyspnea and tachycardia in >90% of patients, which can radiate to the arm 2

Mandatory Initial Diagnostic Workup

Obtain 12-lead ECG within 10 minutes to identify STEMI, ST depression, or ischemic changes, and measure cardiac troponin immediately with repeat according to protocol. 1, 2

• Perform focused cardiovascular examination for murmurs, rales, and signs of heart failure 1
• Chest radiograph to evaluate for mediastinal widening (dissection), pneumothorax, or pneumonia 2
• If pulmonary embolism or dissection suspected, obtain contrast-enhanced chest CT 2
• Pain reproducible with palpation and worsening with specific movements suggests musculoskeletal origin 1

Disposition Based on Initial Workup

• If troponin elevated or ECG shows ischemic changes: admit immediately for ACS management per cardiology protocols 1
• If cardiac workup negative and pericarditis suspected: consider admission or close outpatient follow-up depending on hemodynamic stability 1

Non-Life-Threatening Differential Diagnoses

Gastrointestinal Causes

• Gastroesophageal Reflux Disease (GERD) can cause epigastric or substernal pain radiating to left arm 1
  • Bending forward increases intra-abdominal pressure and precipitates GERD symptoms 1
  • Sensory input from gastrointestinal tract can mimic cardiac pain due to convergence with cardiac input onto spinothalamic tract neurons 5

Musculoskeletal Causes

• Nonspecific arm pain is characterized by vague, diffuse symptoms with disproportionate pain and disability 6
• Cervical radiculopathy from nerve root compression can cause arm pain with paresthesias following specific dermatomal patterns 7
• Brachial plexus pathology or peripheral nerve compression should be considered when pain follows specific nerve distributions 7
• Musculoskeletal pain is suggested when symptoms worsen with specific movements and are reproducible with palpation 1

Neurologic Mechanisms

• Spinal cardiac afferent fibers mediate typical anginal pain via pathways from spinal cord to thalamus and cerebral cortex, involving substance P, glutamate, and TRPV1 receptors 5
• Vagal cardiac afferent fibers likely mediate atypical anginal pain through nucleus of solitary tract and C1-C2 spinal segments 5
• The sensory distribution of symptoms and identification of affected muscles (if weakness present) helps localize pathology 7

Common Pitfalls to Avoid

• Do not assume left-sided chest/arm pain is more specific for MI than right-sided pain; right chest and arm pain actually differentiates MI from non-cardiac causes better than the "classical" left-sided pattern 3
• Do not dismiss cardiac causes in women presenting with atypical pain to back, neck, or jaw rather than classic left arm radiation 5
• Do not attribute all arm pain to specific pathology when psychological and sociological factors significantly contribute to illness presentation 6
• Do not delay ECG and troponin testing to obtain chest X-ray in unstable patients, as this causes treatment delays 4