Kehr’s sign is characterized by the sudden onset of acute pain felt at the tip of the left shoulder. This shoulder pain occurs despite the actual source of the problem being located in the abdomen, specifically within the peritoneal cavity. It is a classic indicator of irritation to the diaphragm, which often signals a serious underlying condition. The irritation is typically caused by the accumulation of blood or other fluids that come into contact with the underside of the diaphragm. Kehr’s sign is recognized as a red flag for significant internal injury, most notably various forms of intra-abdominal hemorrhage.
The Neurological Basis of Kehr’s Sign
The appearance of pain in the shoulder when the injury is below the diaphragm is a textbook example of referred pain. This phenomenon is explained by the shared neurological pathways between the diaphragm and the skin of the shoulder region. The diaphragm, the large dome-shaped muscle separating the chest cavity from the abdomen, receives its sensory supply primarily from the phrenic nerve.
The phrenic nerve originates high up in the neck, specifically from the third, fourth, and fifth cervical spinal nerve roots (C3, C4, and C5). These same nerve roots also supply sensation to the supraclavicular nerves, which innervate the skin over the shoulder tip. When irritating fluids touch the diaphragm, the phrenic nerve transmits a pain signal back to the spinal cord at the C3-C5 level.
Because the brain receives strong pain signals from these shared spinal segments, it cannot accurately distinguish whether the signal originated from the diaphragm or the shoulder. The brain misinterprets the visceral pain from the deep-seated diaphragm as somatic pain originating from the shoulder area. This misinterpretation results in the referred sensation of acute pain felt at the shoulder tip, even though the shoulder itself is completely undamaged.
Conditions That Trigger Kehr’s Sign
The most common and classic pathology associated with Kehr’s sign is a ruptured spleen, which causes a rapid accumulation of blood in the upper left side of the abdominal cavity. The spleen is the most frequently injured internal organ in cases of blunt abdominal trauma, and its rupture leads to hemoperitoneum, where the blood irritates the left hemidiaphragm.
Kehr’s sign can also be triggered by any condition that introduces blood or irritating substances into the peritoneal space near the diaphragm. A life-threatening cause in women of reproductive age is a ruptured ectopic pregnancy, where bleeding from the fallopian tube can spill into the abdomen. A large volume of blood can track upward to irritate the diaphragm, sometimes causing pain in the right shoulder tip if the irritation is on the right side.
Other conditions causing irritation include a liver laceration from trauma, which leads to bleeding near the right hemidiaphragm, or a perforated stomach ulcer that releases gastric contents. Less commonly, inflammatory processes like acute pancreatitis or a subphrenic abscess may also irritate the diaphragm enough to elicit the referred pain.
Why Immediate Medical Attention is Necessary
The presence of Kehr’s sign is considered a serious finding because it generally points to an underlying condition with the potential for life-threatening internal bleeding. Since the sign is often caused by hemoperitoneum, it suggests a significant volume of blood loss into the abdominal cavity, which can rapidly lead to hemorrhagic shock. For this reason, a positive Kehr’s sign must prompt an immediate emergency medical evaluation.
Medical teams will quickly assess for signs of hemodynamic instability, such as low blood pressure and a rapid heart rate, which indicate a state of shock from blood loss. Diagnostic imaging is rapidly employed to confirm the presence and source of the bleeding. A Focused Assessment with Sonography for Trauma (FAST) exam, a quick ultrasound of the abdomen, is often the first step to detect free fluid, presumed to be blood.
If the patient’s condition permits, a computed tomography (CT) scan may be performed to pinpoint the exact location and extent of the injury, such as a splenic tear or liver laceration. If the patient is unstable and actively bleeding, imaging may be bypassed for immediate surgical consultation. The ultimate treatment for a positive Kehr’s sign is not directed at the shoulder pain itself but at surgically controlling the abdominal hemorrhage that is causing the diaphragmatic irritation.