A 29-year-old woman is brought to the emergency department after a motor vehicle collision. She reports diffuse abdominal pain and aching pain over the left shoulder. She has no previous history of shoulder injury. Temperature is 37.1°C (98.8°F), blood pressure is 92/58 mm Hg, pulse is 118/min, and respirations are 22/min. Physical examination shows left upper quadrant abdominal tenderness with guarding. Passive and active range of motion of the left shoulder are normal, and there is no tenderness over the clavicle, acromioclavicular joint, or proximal humerus. Focused abdominal ultrasonography shows free intraperitoneal fluid near the spleen.
The patient’s shoulder pain is most likely referred through sensory afferents entering which of the following spinal cord levels?
The correct answer is:
A) C3-C5
This patient likely has splenic injury with intraperitoneal bleeding irritating the left hemidiaphragm, causing referred pain to the left shoulder. Sensory innervation of the central diaphragm is carried by the phrenic nerve, which arises from spinal cord levels C3-C5. Referred pain occurs because visceral or diaphragmatic afferents and somatic afferents from the shoulder region converge on overlapping spinal cord segments. The supraclavicular nerves that supply the shoulder region also arise from cervical levels, so diaphragmatic irritation may be perceived as shoulder pain.
Answer choice B: T1-T4, is incorrect. Upper thoracic spinal levels are associated with referred pain from some thoracic structures, such as cardiac pain radiating to the chest or medial arm. This patient’s shoulder pain in the setting of splenic injury and diaphragmatic irritation is better explained by phrenic nerve afferents entering C3-C5.
Answer choice C: T5-T9, is incorrect. These levels are associated with foregut visceral afferents, which can refer pain to the epigastric region. They do not explain isolated shoulder pain caused by irritation of the central diaphragm.
Answer choice D: T10-L1, is incorrect. These levels are associated with hindgut, pelvic, and some lower abdominal referred pain patterns, including pain from structures such as the distal colon or upper ureter. They are not the primary pathway for referred shoulder pain from diaphragmatic irritation.
Answer choice E: S2-S4, is incorrect. S2-S4 carries parasympathetic outflow to pelvic organs and visceral afferents from many pelvic structures below the pelvic pain line. These levels are not responsible for referred shoulder pain after diaphragmatic irritation.
Key Learning Point
Referred shoulder pain from diaphragmatic irritation is transmitted by the phrenic nerve, whose sensory afferents enter the spinal cord at C3-C5.
