What is the differential diagnosis for an 18‑year‑old female with acute right parasternal throbbing chest pain that began while laughing, with prior brief episodes, anxiety treated with buspirone, nicotine vaping, marijuana use, occasional alcohol, negative ECG, cardiac enzymes, chest radiograph, and mild hypokalemia?

Differential Diagnosis for Acute Right Parasternal Chest Pain in an 18-Year-Old Female

This is most likely costochondritis triggered by the mechanical stress of laughter, but you must first exclude acute coronary syndrome, pulmonary embolism, and pneumothorax before making this diagnosis.

Immediate Life-Threatening Exclusions (First 10 Minutes)

Acute Coronary Syndrome

• Obtain a 12-lead ECG within 10 minutes and measure high-sensitivity cardiac troponin immediately, even though ACS is unlikely in an 18-year-old; women frequently present with atypical symptoms including sharp, localized pain. 1, 2
• Sharp or pleuritic chest pain does not exclude ACS—approximately 13% of patients with pleuritic-type pain have acute myocardial ischemia. 2, 3
• Nicotine vaping is a significant risk factor for coronary vasospasm and endothelial dysfunction in young adults, making cardiac evaluation mandatory. 2
• A completely normal physical examination does not exclude uncomplicated myocardial infarction. 2

Pulmonary Embolism

• Assess for tachycardia (present in >90% of PE cases), tachypnea, and oxygen saturation to screen for PE, particularly given nicotine vaping as a prothrombotic risk factor. 2, 3
• The combination of right-sided pleuritic pain and substance use (nicotine, marijuana) warrants PE consideration despite young age. 3

Pneumothorax

• Examine for unilateral decreased breath sounds and hyperresonant percussion on the right side; spontaneous pneumothorax can occur in young, thin individuals and may be triggered by forceful expiratory efforts during laughter. 2, 3
• Marijuana smoking increases the risk of spontaneous pneumothorax through bullae formation. 3

Most Likely Diagnosis: Costochondritis

Clinical Features Supporting This Diagnosis

• Right parasternal location with reproducible tenderness on palpation of costochondral junctions is pathognomonic for costochondritis. 2, 4
• Costochondritis accounts for approximately 43% of chest pain presentations when cardiac causes are excluded. 2
• Pain triggered by laughter is highly characteristic—fits of laughter generate sudden, repetitive expiratory efforts at 4.6 Hz frequency, creating mechanical stress on costochondral joints and decreasing functional residual capacity by 1.55 liters. 5
• The throbbing quality reflects inflammation of the costochondral junction with localized hyperemia. 4
• Prior brief episodes suggest recurrent mechanical irritation of the same anatomical site. 4

Why Laughter Triggers Costochondral Pain

• Laughter produces remarkable dynamic compression of airways and sudden increases in esophageal pressure well beyond maximum expiratory flow thresholds. 5
• The diaphragm actively contracts during laughter to prevent excessive abdominal pressure transmission, creating shearing forces at costochondral attachments. 5
• These repetitive mechanical stresses can inflame costochondral junctions, particularly in individuals with pre-existing subclinical inflammation. 4, 5

Other Differential Considerations

Anxiety-Related Chest Pain (Psychogenic)

• History of controlled anxiety on buspirone makes psychogenic chest pain a consideration, particularly with recurrent episodes. 1
• In low-risk chest pain patients without cardiac disease, anxiety syndromes exceed coronary artery disease by almost 10-fold. 1
• However, do not attribute pain to anxiety until after completing full cardiac workup—this is a diagnosis of exclusion. 1

Esophageal Spasm

• Esophageal spasm can present as localized chest pain and may be triggered by laughter-induced increases in intra-abdominal pressure. 1, 2
• Do not rely on nitroglycerin response to differentiate cardiac from esophageal pain, as both may respond. 1, 2

Precordial Catch Syndrome

• Brief, sharp, localized chest pain in young adults that resolves spontaneously; however, this patient's pain has persisted for one hour, making this less likely. 4

Significance of Mild Hypokalemia (K+ 3.4)

• Potassium of 3.4 mEq/L is minimally low and unlikely to be the primary cause of chest pain. 1
• However, hypokalemia can predispose to cardiac arrhythmias; ensure ECG shows no QT prolongation or U waves. 2
• Consider causes: inadequate dietary intake, alcohol use, or marijuana-induced hyperemesis with vomiting (not reported here). 1

Diagnostic Algorithm

1. Immediate (0-10 minutes):

   • 12-lead ECG to exclude STEMI, ischemic changes, or arrhythmias 1, 2
   • High-sensitivity cardiac troponin 1, 2
   • Vital signs including bilateral blood pressures, oxygen saturation 2, 3
   • Focused cardiovascular and pulmonary examination 2

2. If ECG and initial troponin normal (10-30 minutes):

   • Chest radiograph (PA and lateral) to exclude pneumothorax, pneumonia 2, 3
   • Palpate all costochondral junctions bilaterally for reproducible tenderness 2, 4
   • Assess pain with chest wall movement, deep breathing, arm elevation 2, 4

3. If initial workup negative (3-6 hours):

   • Repeat troponin at 3-6 hours to definitively exclude evolving myocardial injury 2
   • Correct potassium to >3.5 mEq/L 1

4. If all cardiac testing negative and costochondral tenderness present:

   • Diagnose costochondritis 2, 4
   • Prescribe ibuprofen 600-800 mg three times daily for 1-2 weeks 2
   • Advise avoidance of movements that exacerbate pain 2
   • Provide reassurance about benign prognosis 1, 4

Critical Pitfalls to Avoid

• Do not dismiss cardiac causes based solely on age (18 years) and reproducible chest wall tenderness—up to 7% of patients with palpable tenderness still have ACS. 2, 3
• Do not assume sharp, localized pain excludes ACS in a young woman with vaping history. 2
• Do not attribute symptoms to anxiety without completing full cardiac exclusion, as this leads to missed diagnoses and repeated ED visits. 1
• Do not discharge after a single normal troponin if drawn <6 hours from symptom onset. 2
• Recognize that nicotine vaping is not benign—it causes endothelial dysfunction, coronary vasospasm, and prothrombotic states even in teenagers. 2

Disposition and Follow-Up

• If serial troponins and ECGs remain normal, chest X-ray is clear, and costochondral tenderness is reproducible, discharge home with NSAIDs and primary care follow-up in 3-5 days. 2
• Counsel strongly on smoking/vaping cessation—nicotine is a major modifiable cardiovascular risk factor. 6
• If pain recurs frequently without physiological cause after thorough workup, consider referral to cognitive-behavioral therapy for anxiety-related chest pain. 1