What could be causing pain in the upper left chest area when lying on my side?

Upper Left Chest Pain When Lying on Side: Most Likely Musculoskeletal

Positional chest pain that occurs specifically when lying on your side is almost certainly musculoskeletal in origin and not cardiac ischemia. 1

Why This Is Likely Musculoskeletal

The 2021 AHA/ACC/CHEST guidelines explicitly state that "positional chest pain is usually nonischemic (eg, musculoskeletal)" 1. The key distinguishing features that point away from cardiac disease include:

• Pain triggered by specific body positions (lying on side) rather than exertion or emotional stress 1
• Sharp or pleuritic quality that increases with certain positions, which is "unlikely related to ischemic heart disease" 1
• Absence of typical anginal triggers such as physical exercise or emotional stress 1

The ACC/AHA guidelines further clarify that pericarditis can cause positional chest pain that "increases in supine position," but this typically presents with fever and a friction rub on examination 1

Physical Examination Findings to Confirm

You should check for reproducible chest wall tenderness by palpating the costochondral joints and chest wall muscles. 2 The presence of:

• Tenderness at costochondral joints suggests costochondritis or Tietze syndrome 1, 2
• Reproducible pain with chest wall palpation confirms muscular chest wall pain 2
• Point tenderness makes cardiac ischemia less likely 2

Critical Red Flags That Would Change This Assessment

Despite the reassuring positional nature, you must still rule out life-threatening causes if ANY of these features are present 2:

• Diaphoresis, nausea, vomiting, or cold sweats 2
• Dyspnea, tachycardia, or hypotension 2
• Radiation to arm, jaw, neck, or back 2
• Symptoms that interrupt normal activity 2
• Sudden onset "ripping" quality (suggests aortic dissection) 1

When to Seek Emergency Evaluation

If the pain is purely positional without red flags, emergency evaluation is not required. 1 However, immediate ED evaluation is mandatory if:

• The pain becomes constant rather than positional 1
• Any of the red flag symptoms listed above develop 2
• You have cardiac risk factors (hypertension, diabetes, known coronary disease) and the pain character changes 2

Common Pitfall to Avoid

Do not assume that left-sided chest pain automatically means cardiac disease. 1 The ACC/AHA guidelines specifically note that "symptoms on the left or right side of the chest, stabbing, sharp pain" can occur even in patients with myocardial ischemia (particularly in diabetes, women, and elderly patients), but when combined with positional triggers and absence of exertional triggers, musculoskeletal causes are far more likely 1

Recommended Management Approach

For positional chest pain without red flags:

• Trial of NSAIDs for presumed costochondritis or muscular strain 2, 3
• Avoid positions that trigger the pain while inflammation resolves 2
• Follow up if symptoms persist beyond 2-3 weeks or change in character 2
• Consider osteopathic manipulative treatment if available, which can be effective for musculoskeletal chest pain 3

Bold: The positional nature of your pain (occurring specifically when lying on your side) makes this musculoskeletal rather than cardiac, but you should still have a physical examination to confirm chest wall tenderness and ensure no red flag features are present.