Differential Diagnosis for Left Shoulder Pain Radiating Down the Arm

• Single Most Likely Diagnosis
  • Subacromial Bursitis or Rotator Cuff Tendinitis: The patient's presentation of shoulder pain radiating down the arm, a tense sore spot at the junction of the lateral upper arm and superior shoulder-clavicular region, and severely affected range of motion are classic signs of subacromial bursitis or rotator cuff tendinitis. The onset of pain without a clear triggering event and the partial relief with ibuprofen also support this diagnosis.
• Other Likely Diagnoses
  • Adhesive Capsulitis (Frozen Shoulder): Although less likely given the acute onset, adhesive capsulitis could present with severe pain and limited range of motion. The discovery of a tense sore spot could be indicative of inflammation around the shoulder joint.
  • Cervical Radiculopathy: The radiation of pain down the arm could suggest a cervical spine origin, such as a herniated disc or foraminal stenosis, irritating a nerve root.
  • Thoracic Outlet Syndrome: Compression of the brachial plexus or subclavian vessels could cause pain in the shoulder and arm, especially if the patient's job involves repetitive movements that could exacerbate the condition.
• Do Not Miss Diagnoses
  • Myocardial Infarction (MI) or Angina: Although less common, cardiac conditions can refer pain to the shoulder and arm. Given the potential severity of missing an MI, it's crucial to consider this, especially if the patient has risk factors for cardiovascular disease.
  • Pulmonary Embolism: Similar to MI, a pulmonary embolism can cause referred pain to the shoulder and arm, particularly if the embolism involves the upper lobe of the lung.
  • Spinal Cord Injury or Compression: Acute spinal cord compression or injury could present with arm pain and limited mobility, making it essential to rule out, especially if there's a history of trauma or malignancy.
• Rare Diagnoses
  • Pancoast Tumor: A tumor at the apex of the lung can cause shoulder and arm pain due to invasion of the brachial plexus.
  • Osteonecrosis of the Humeral Head: Although rare, osteonecrosis could cause severe shoulder pain, especially if there's a history of steroid use, trauma, or other risk factors.
  • Infectious or Inflammatory Arthritis: Conditions like septic arthritis, rheumatoid arthritis, or other autoimmune diseases could present with acute shoulder pain and limited range of motion, though these would typically be accompanied by systemic symptoms or other joint involvement.