Types of Abdominal Pain

Abdominal pain is one of the most common presenting symptoms that leads to EMS activation and transport. There are three key types of pain: somatic, visceral, and referred. Within these three types, there is also acute and chronic pain. This section will review the nature of abdominal pain and some of its common sources. 

Pain as a Warning Signal

Pain, however, is a warning signal that gets someone's attention even if bleeding or dysfunction are not present or identifiable. Whether it is abdominal or not, all pain is generally divided into two distinct categories:

1. ACUTE PAIN: conduction along the FAST, MYELINATED pain fibers. Acute pain is a warning signal. (Just like the Godfather, the brain insists on hearing bad news immediately!)
2. CHRONIC PAIN: -unremitting conduction along the SLOW, UNMYELINATED pain fibers. Chronic pain is a disease. (Think of it as the body's way of whining.)

NOCICEPTORS: pain receptors in skin and other tissues or organs. The process of Nociception perceives pain signals. These have a threshold above which a stimulus will cause it to fire. This is why pressing or touching doesn't hurt, but a hammer will. 

MYELIN: a fatty substance made from cholesterol by the glial nerve cells which, via a series of insulation and insulation gaps, allows nerve conduction to "skip" along more rapidly. Myelinization makes nerve conduction much faster, up to 120 meters/second, compared to unmyelinated fibers (as low as 1/2 meter/second). Things that NEED to get our attention that do it QUICKLY aid in survival, e.g., touching a hot stove. The diameter of the nerve fiber also determines the speed of conduction: the wider the nerve fibers, the faster they conduct a signal.

In the field, acute pain is the most frequent complaint requiring assessment from EMS responders. Most consider pain from trauma to be the most challenging aspect of the work. Still, abdominal pain is a "thinking" emergency, particularly challenging because of the many organ systems to be considered (Liver, gallbladder, large and small intestines, kidney/ureters/bladder, and the reproductive organs.)

Types of Pain

Pain receptors (nociceptors) in the abdomen respond to mechanical (distention/obstructive) and chemical (bacterial and inflammatory) stimuli.

A. SOMATIC PAIN: Patients with somatic pain can usually pinpoint the exact location of their discomfort. They may describe the pain as sharp, cutting, or searing, often feeling intense and immediate. This type of pain is usually associated with issues like trauma, inflammation of the parietal peritoneum, or other conditions that directly affect the abdominal wall or peritoneum. Examples: Acute appendicitis involving the parietal peritoneum may cause sharp, localized pain in the lower right quadrant. Diverticulitis, when involving inflammation near the peritoneum, can present with localized pain in the lower left quadrant.

B. VISCERAL PAIN: Visceral pain is more diffuse and less localized. Patients may describe it as a deep, aching, or cramping sensation. They often find it difficult to pinpoint the exact location of the pain, instead indicating a general area, such as the middle of the abdomen. This type of pain is typically associated with organ distention, inflammation, or ischemia. For instance, a patient with early appendicitis might feel a dull, poorly localized pain around the umbilicus before it localizes to the right lower quadrant as the inflammation spreads.
Examples: Early appendicitis may present as dull, poorly localized pain around the umbilicus. Kidney infections (pyelonephritis) can cause visceral pain in the flanks or lower back due to inflammation of the renal pelvis.

C. REFERRED PAIN: Referred pain occurs when pain is felt in a location distant from the actual site of the pathology due to shared nerve pathways. Patients might present with pain in areas that seem unrelated to their abdominal complaint. For example, a patient with gallbladder disease (cholecystitis) might report right shoulder pain, or someone with a splenic injury may experience left shoulder pain (Kehr’s sign).
Examples: Gallbladder disease (cholecystitis) may cause right shoulder pain. Splenic injury can produce left shoulder pain (Kehr’s sign). A bowel obstruction may lead to referred pain patterns depending on the area of involvement.

When assessing a patient with abdominal pain, distinguish between these types of pain, as each provides clues to the underlying cause. Somatic pain suggests a localized issue, often involving the peritoneum or abdominal wall; visceral pain points towards internal organs, often with a more diffuse or generalized presentation; and referred pain can signal pathology that might not be immediately obvious, necessitating a broader differential diagnosis.

Understanding the Transition from Acute to Chronic Pain

One of the most common causes of severe, long-term chronic pain is the inadequate treatment of acute pain. When acute pain is not properly managed, it can lead to changes in the nervous system that make the pain persistent and more difficult to treat.

At the spinal level, when the neuron that transmits pain signals to the brain (the interneuron) is repeatedly exposed to intense pain signals, it can become overwhelmed. Initially, this interneuron works to reduce the pain signal (acting as an inhibitory neuron). However, with constant stimulation from acute pain, it can change its function and start to amplify the pain signals instead (becoming an excitatory neuron). This shift can activate other pain pathways in the spinal cord, leading to the development of chronic pain syndromes. These chronic pain conditions can persist long after the original injury has healed and can be very challenging to manage.

Call to Action: Treat Acute Pain Promptly

For EMS responders, aggressively treating acute pain when it is safe can prevent the development of chronic pain and improve long-term outcomes for patients. However, care must be taken to ensure that pain relief does not mask symptoms critical for diagnosing the underlying cause of the pain.