Which nerve is commonly involved in referred pain to the shoulder during pericarditis?

The Phrenic Nerve is Responsible for Referred Pain to the Shoulder in Pericarditis

The correct answer is B) Phrenic nerve.

The phrenic nerve is the primary nerve pathway responsible for referred pain to the shoulder during pericarditis. This occurs through a well-established neuroanatomical connection between the pericardium and the shoulder region.

Anatomical Basis for Referred Shoulder Pain

The phrenic nerve provides sensory innervation to the pericardium and parts of the diaphragm. When the pericardium becomes inflamed during pericarditis, the following mechanism occurs:

• The phrenic nerve carries sensory information from the inflamed pericardium
• The phrenic nerve originates from the C3-C5 cervical segments (primarily C4)
• The same cervical segments give rise to the supraclavicular nerves that supply the shoulder region
• This shared neuroanatomical pathway explains why pericardial inflammation is perceived as pain in the shoulder area

Clinical Presentation of Pericarditis

Pericarditis typically presents with:

• Chest pain (sharp, pleuritic, often improved by sitting forward)
• Pericardial friction rub on auscultation
• ECG changes (widespread ST elevation with PR depression)
• Possible pericardial effusion

When shoulder pain occurs with these symptoms, it strongly suggests pericardial involvement with referred pain through the phrenic nerve pathway 1.

Differential Diagnosis of the Answer Choices

1. Vagus nerve (A): While the vagus nerve provides parasympathetic innervation to the heart, it is not responsible for referred pain to the shoulder in pericarditis.

2. Phrenic nerve (B): The correct answer. The phrenic nerve innervates the pericardium and shares neuroanatomical connections with the shoulder region through C3-C5 nerve roots 2, 3.

3. Intercostal nerves (C): These nerves supply the intercostal muscles and thoracic wall but do not explain the specific pattern of referred pain to the shoulder in pericarditis.

4. Sympathetic nerves (D): While sympathetic nerves innervate the heart, they are not the primary pathway for referred shoulder pain in pericarditis.

Clinical Significance

Understanding this referred pain pathway is clinically important because:

• Shoulder pain may be the presenting or predominant symptom in some patients with pericarditis
• Recognition of this pattern helps differentiate pericarditis from other causes of chest or shoulder pain
• In cases of diaphragmatic irritation (including from pericardial inflammation), pain is classically felt at the shoulder tip due to this phrenic nerve pathway 3

Management Implications

When evaluating a patient with shoulder pain and suspected pericarditis:

• Look for other cardinal signs of pericarditis (chest pain, friction rub, ECG changes)
• Perform echocardiography to assess for pericardial effusion
• Consider inflammatory markers (CRP, ESR) to evaluate for pericardial inflammation
• Treat the underlying pericarditis rather than focusing on symptomatic treatment of the shoulder pain

The phrenic nerve pathway explains why patients with pericarditis may present with shoulder pain as a prominent symptom, making this an important clinical association to recognize in cardiovascular assessment.