Functional Abdominal Pain and Visceral Hyperalgesia

Note: This is a revised version of an article first published in 2008.

Many children with complex medical conditions experience significant abdominal pain that cannot be easily diagnosed or understood. Despite significant obvious symptoms of pain, no anatomical problems show up on X-ray or other imaging, and there is no sign of ongoing infection or autoimmune disease.

These types of pain are commonly grouped together under the heading of Functional Abdominal Pain, which can be chronic and debilitating to children, as well as puzzling to doctors. Functional abdominal pain, as defined by the AAP Subcommittee on Chronic Abdominal Pain in Children, is, “Abdominal pain without demonstrable evidence of a pathologic condition, such as an anatomic, metabolic, infectious, inflammatory, or neoplastic disorder; functional abdominal pain may present with symptoms typical of functional dyspepsia, irritable bowel syndrome, abdominal migraine, or functional abdominal pain syndrome.”¹

While in many children, functional abdominal pain is a minor inconvenience that often resolves with time or age, in others, it can severely limit the ability to participate in customary childhood activities like school and play, or even prevent a child from using the gut at all. The latter is particularly likely to occur in children with other complex medical issues, neurological conditions, or frequent gut surgeries.

How Functional Abdominal Pain and Visceral Hyperalgesia Work

Functional abdominal pain is not well understood, but involves the Enteric Nervous System, or the system of motor and sensory nerves that are present within the entire gut. Nerves may be over-sensitized, or the gut may produce chemicals that trigger a pain response.

Many severe cases of functional abdominal pain are the result of Visceral Hyperalgesia, which may also be called Visceral Hypersensitivity, a term that simply means an individual has increased sensitivity to pain in the visceral system of internal organs like the stomach, intestines, or pancreas. Normally, when one eats or drinks, the stomach and intestines stretch to accommodate the meal with no discomfort whatsoever. But in a child with visceral hyperalgesia, the mere act of filling the stomach or intestine with a small amount of fluid or food triggers the nerves in the gut or brain to respond as if something painful has been introduced. Studies on children with irritable bowel syndrome and recurrent abdominal pain have shown that children with these conditions have a much lower threshold for pain in the digestive tract.²  If motor nerves in the gut are affected, a motility disorder develops, and when sensory nerves are affected, visceral hyperalgesia is often the result. It is common for both types of disorders to be present in tandem.

What is painless to most children feels excruciatingly painful to children with visceral hyperalgesia. Children with this diagnosis commonly have pain responses to one or more types of agents: pain due to digestive processes such as food entering the gut or liquid stretching the gut; significantly increased pain due to infections, viruses, or other external insults on the gut; and a pain response to psychological events such as anxiety or fear. In many children, all that is needed to cause pain is the introduction of food into the stomach and intestine. Once the pain signal has been turned on, the pain may persist for weeks, months, or years, or may come in intermittent cycles.

The Causes of Visceral Hyperalgesia

In the past, functional abdominal pain was often associated with anxiety, behavioral problems, or other psychological symptoms. While children with abdominal pain are more likely to present with these psychological disorders, there are many children with no underlying psychological or behavioral issues who nonetheless experience significant and remarkable abdominal pain.

In many cases, visceral hyperalgesia occurs after a virus, illness, or other external assault on the gut. The illness causes temporary damage to the mucus lining of the stomach and intestines, resulting in stomach pain. This pain then sensitizes the nerves in the stomach or intestines, causing them to be left “turned on” and hypersensitive to pain.

Other gastrointestinal conditions such as pancreatitis, motility disorders, cyclic vomiting (abdominal migraine), or even severe reflux may also trigger visceral hyperalgesia. In some children, only one part of the digestive tract is affected, while in others, most or all of stomach and bowel is impacted.

Another common cause of visceral hyperalgesia is surgery to the stomach or intestine. Surgeries to place a feeding tube, correct anatomical malformations, or alter the bowel or stomach in any way can lead to visceral hyperalgesia.

Children with severe neurological impairments, including children with hypoxic ischemic encephalopathy, cerebral palsy, and a wide range of other neurological conditions, seem to be particularly primed to experience visceral hyperalgesia and other forms of functional abdominal pain. This is likely due to damage to the brain and nerves caused by the underlying condition.

Other conditions, including reflux, bacterial overgrowth of the gut, and autoimmune conditions such as celiac or inflammatory bowel disease may also trigger increased visceral hyperalgesia. Treatment of the underlying condition often relieves the pain in these instances.

Symptoms of Functional Abdominal Pain

Functional abdominal pain includes a wide range of symptoms and syndromes, including generalized abdominal pain, dyspepsia, irritable bowel syndrome with diarrhea or constipation, nausea, vomiting, retching, bloating, pain with defecation, and a feeling of fullness.

Symptoms of visceral hyperalgesia, in particular, are vague and often very difficult to categorize, especially in young children and children with neurological and cognitive impairments. All diagnosed children experience pain, but the pain may be localized, diffuse, sharp, dull, burning, intermittent, or constant. Many children with severe visceral hyperalgesia also have other symptoms such as bloating, constipation, diarrhea, retching, or vomiting. This is especially the case when both the sensory and motor nerves of the gut are affected. In many children, pain triggers gastrointestinal symptoms like retching and vomiting, which in turn create even more pain and distress. These additional symptoms, coupled with pain, may be so severe that a feeding tube or even a central line must be placed for enteral or intravenous feedings.

In most cases, functional abdominal pain is a diagnosis of exclusion, after all tests for organic or anatomical disorders have come back negative. Conditions that should be excluded include anatomical malformations, autoimmune disorders, infections, food allergies, and other similar conditions. It is typical for a child to have some sort of imaging, which may include an X-ray, CT scan, or endoscopy, as well as basic lab work to rule out liver, pancreas, and kidney problems.

Treatment of Visceral Hyperalgesia

Many children with visceral hyperalgesia, especially when it occurs after a viral illness or infection, will recover in time with no treatment. Other children, especially those with underlying gut issues or neurological conditions, may require substantial intervention to provide adequate nutrition and manage pain and additional gastrointestinal symptoms. In most cases, with adequate management by a pediatric gastroenterologist who specializes in motility issues or functional abdominal pain, a plan to manage symptoms can be developed to reduce the child’s pain.

Many small lifestyle changes can be tried first to calm visceral hyperalgesia. Diet changes, consuming or feeding small meals, and regularizing gut flora with probiotics may help some children. Children with feeding tubes can try slow, continuous feeds or frequent small boluses. Some children may also improve by receiving continuous feedings directly into the jejunum via a GJ or J-tube. Children with extremely severe visceral hyperalgesia may need a central line and TPN (IV) feedings to allow total gut rest.

Children with acute-onset visceral hyperalgesia may benefit from typical acute pain medications ranging from over-the-counter pain killers to opioids. In general, children who need acute pain relief are given non-narcotic pain relievers or pseudo-opiates, since narcotics and opiates disturb motility of the gut and may worsen gut function in the long run.

Once visceral hyperalgesia has become more habitual, other pain medications may be more appropriate. Commonly used medications include tricyclic antidepressants, especially Amitriptyline (Elavil), Nortriptyline (Pamelor), and Imipramine (Tofranil). Medications to treat neuropathic pain have also proven helpful, especially Gabapentin (Neurontin) and its cousin Pregabalin (Lyrica). Other possible medications include Nifedipine (Procardia); Dicyclomine (Bentyl), Alosetron (Lotronex) or Tegaserod (Zelnorm) for children with more intestinal issues; Ondansetron (Zofran) to prevent vomiting; Hyoscyamine (Levsin) for children with spasms; and other anticholinergic and anti-nausea medications.

Older children, particularly those with concurrent psychological disorders, may benefit from behavioral therapy or consultation with a chronic pain psychologist.

Improvement is Possible!

Visceral hyperalgesia is a difficult condition to diagnosis, understand, and treat. But with proper treatment, most children can resume the normal activities of childhood. Many will even overcome their visceral hyperalgesia over a period of six to eighteen months.

In general, success depends entirely on finding a pediatric gastroenterologist or other physician familiar with functional abdominal pain and visceral hyperalgesia. Doctors at motility clinics and in palliative care programs, along with complex care physicians, may have more experience treating this type of pain. It is worth seeking out an expert, especially if your child’s quality of life is being profoundly affected.

¹ American Academy of Pediatrics Subcommittee on Chronic Abdominal Pain. Chronic Abdominal Pain in Children. Pediatrics 2005;Vol. 115 No. 3:812-815.

² Di Lorenzo C, Youssef NN, Sigurdsson L, Scharff L, Griffiths J, Wald A. Visceral hyperalgesia in children with functional abdominal pain. Pediatrics 2001;Vol. 139 No. 6:838-843.