Diagnosis: Herpes Zoster (Shingles)
The most likely diagnosis is herpes zoster (shingles), which characteristically presents as an erythematous papule with needle-pricking (sharp, stabbing) pain in a unilateral dermatomal distribution on the chest wall in young adults. 1, 2
Clinical Reasoning
Key Diagnostic Features
- Dermatomal distribution: The unilateral left-sided chest location is classic for herpes zoster, which follows specific nerve root distributions 1
- Pain quality: "Needle-pricking pain" is the hallmark neuropathic pain pattern of herpes zoster, often described as sharp, stabbing, or burning, and may precede or accompany the rash 1, 2
- Age and presentation: While more common in older adults, herpes zoster can occur in immunocompetent young adults, particularly in the thoracic dermatomes (most common site) 3
Physical Examination Findings to Confirm
- Unilateral dermatomal rash: Look for grouped vesicles on an erythematous base that do not cross the midline 1
- Pain triggered by light touch: Allodynia (pain from normally non-painful stimuli) in the affected dermatome is characteristic 1
- Prodromal symptoms: Pain may precede visible skin lesions by 1-5 days 3
Critical Differential Diagnoses to Exclude
Life-Threatening Causes (Must Rule Out First)
- Acute coronary syndrome: While sharp pleuritic pain makes cardiac ischemia less likely, 13% of patients with pleuritic pain have acute myocardial ischemia 2, 4
- Pneumothorax: Would present with dyspnea, unilateral absent breath sounds, and hyperresonant percussion 4, 5
- Pulmonary embolism: Typically presents with dyspnea followed by pleuritic pain, tachycardia, and tachypnea 2, 4
- Pericarditis: Sharp pain that worsens supine and improves sitting forward, with possible friction rub 1, 4
Other Common Causes
- Costochondritis: Tenderness of costochondral joints on palpation, but 7% of patients with reproducible chest wall pain still have acute coronary syndrome 4
- Pneumonia: Would show fever, productive cough, regional dullness, and egophony 4
Diagnostic Workup
Immediate Evaluation
- ECG within 10 minutes: To exclude STEMI, pericarditis patterns, or signs of pulmonary embolism 4
- Chest radiograph: To evaluate for pneumothorax, pneumonia, or pleural effusion 4
- Vital signs: Tachycardia and tachypnea are present in >90% of pulmonary embolism cases 4
- Cardiac troponin: Measure as soon as possible to exclude myocardial injury 4
If Initial Testing Normal
- Clinical diagnosis of herpes zoster: Based on characteristic unilateral dermatomal pain and erythematous papule 1
- Tzanck smear or PCR: Can confirm varicella-zoster virus if diagnosis uncertain 3
- Consider HIV testing: In young adults with herpes zoster, especially if severe or recurrent 3
Treatment Approach
For Confirmed Herpes Zoster
- Antiviral therapy within 72 hours of rash onset: Acyclovir 800 mg 5 times daily, valacyclovir 1000 mg 3 times daily, or famciclovir 500 mg 3 times daily for 7 days 3
- Pain management: NSAIDs for mild pain; consider gabapentin or pregabalin for neuropathic pain 3
- Topical therapy: Calamine lotion or topical lidocaine for symptomatic relief 3
Critical Pitfalls to Avoid
- Do not assume reproducible chest wall tenderness excludes serious pathology: 7% of patients with palpable tenderness have acute coronary syndrome 4
- Do not use nitroglycerin response as diagnostic: Relief with nitroglycerin does not confirm or exclude myocardial ischemia 4
- Do not delay evaluation if pain is sharp/pleuritic: Sharp chest pain that increases with inspiration makes ischemic heart disease less likely but does not completely rule it out 2, 4
When to Hospitalize
- Ophthalmic involvement: Requires urgent ophthalmology consultation 3
- Immunocompromised patients: May require IV antiviral therapy 3
- Disseminated disease: More than 20 lesions outside primary dermatome 3
- Severe pain uncontrolled with oral medications: May require parenteral analgesia 3