Perhaps psychiatrists and gastroenterologists should talk shop more often, given the many interactions between the brain and the gut. FIG1

The well-traveled connection between the central nervous system and the digestive system may carry the effects of illness or treatment in either direction, Catherine Crone, M.D., an associate professor of psychiatry at George Washington University School of Medicine and a clinical professor of psychiatry at Virginia Commonwealth University, said at APA's 2009 annual meeting in San Francisco in May.

The bidirectional pathways between brain and gut encompass the autonomic nervous system and the HPA axis. The limbic system not only controls the gut but also oversees homeostasis, emotionality, social interaction, threat avoidance, and survival responses. Serotonin plays an important communications role in both. Medications intended to treat disorders in one system may affect the other. Symptoms and risk factors may overlap.

Both psychiatrists and gastroenterologists need to know about that overlap and how to manage patients whose illnesses fall into that space.

"The GI tract is a multiorgan system, and there are a lot of places along the way besides the stomach and intestines, including the liver and the pancreas," said Crone.

Crone divides GI illnesses into functional and structural disorders, a nomenclature that may ring bells with psychiatrists.

"These connections may explain how psychosocial factors, personality, and stress influence the onset and course of functional GI disorders," said Crone.

Structural disorders include dysphagia, gastroesophageal reflux disease (GERD), and peptic ulcer disease. Dysphagia affects up to 22 percent of U.S. adults over age 50, with higher prevalences in nursing home and hospital populations, said Crone. Side effects of psychotropic drugs such as antipsychotics may contribute to dysphagia due to oversedation, xerostomia, or dystonia. Symptoms of Parkinsonism or tardive dyskinesia can be treated by lowering the antipsychotic dose or discontinuing or switching medications.

GERD is the most common cause of noncardiac chest pain and affects 20 percent to 30 percent of people in Western countries. Standard treatment uses antacids, proton pump inhibitors, and H2 blockers. In some patients, antidepressants (tricyclics, SSRIs, or trazodone) appear to improve well-being, sleep, and gastric transit, while low-dose tricyclics can reduce visceral hypersensitivity.

Peptic ulcer disease was once viewed as a purely psychosomatic disorder caused by stress. Today, stress is seen as an independent risk factor in combination with infection by Helicobacter pylori. Antidepressants may be a useful adjunct treatment to reduce stress even if depression is not diagnosed.

"But use SSRIs with caution because they can reduce platelet aggregation and contribute to risk of GI bleeding," said Crone.

Depression is a risk factor for inflammatory bowel disease (Crohn's disease, ulcerative colitis). Patients with these illnesses have three times the rate of depression of the general population, and depression is also a risk factor for treatment failure when using infliximab. Antidepressants such as paroxetine, buproprion, or phenelzine have been used successfully to reduce psychiatric symptoms and lessen distress. Buproprion also lowers levels of tumor necrosis factor-α, which may contribute to remission, she said.

Treatment becomes complicated with patients who have intestines shortened by Roux-en-Y gastric bypass surgery. The procedure reduces the absorptive surface of the small intestine as well as transit time through the bowel.

"Medications are less predictably absorbed under these circumstances," said Crone. "When possible, use drugs in aqueous solution rather than in suspension or solid form."

Orally disintegrating medication forms are another alternative. Extended-release formulations should be avoided because the tablets pass undissolved through the shortened intestine before they can dissolve. In any case, monitoring blood levels of drugs is necessary because absorption is so hard to predict.

Functional diseases, in contrast, lack structural, physiological, or biochemical abnormalities (or at least gastroenterologists haven't discovered them yet).

Often patients have high rates of comorbid psychiatric disorders, such as depression, neuroticism, hostility, or a history of trauma, she said." Psychotropics can often help these patients, even if we don't know why."

The prototypic functional GI disease, irritable bowel syndrome, affects 7 percent to 10 percent of people worldwide. Patients use 50 percent more health care resources than their matched counterparts without the disorder, partly because they somaticize and overinterpret normal physiological processes, said Crone. Furthermore, between 40 percent and 94 percent of patients also have Axis I disorders.

Antidepressants are often part of a treatment regimen, although not always. Tricyclics and SSRIs are better than placebo in reducing symptoms, even at subtherapeutic doses. Since irritable bowel syndrome presents with either diarrhea- or constipation-predominant symptoms, choice of an antidepressant should be based on side effects that counteract that tendency.

Liver dysfunction can alter pharmacokinetics and hamper therapeutic drug monitoring, said Crone. Greater dysfunction results in prolonged half-life delays in the drug's steady state. The Child-Pugh Score is used to determine severity of liver disease and can be used to estimate inadequacy of drug metabolism.

"It's better to start with low doses and make smaller dosage increases, further apart, when titrating medications," she said." Avoid drugs like lithium or clozapine with a narrow therapeutic window or long half-lives, and remember that many patients with liver disease also have renal impairment, which may require further dosage adjustment."

Finally, psychiatrists and gastroenterologists should remain in close contact about patients whose diagnoses overlap the two specialties, said Crone in an interview.

"Coordinating care is always a challenge and something that psychiatrists often fail at when it comes to communicating with other health care providers," she said. "I do think calls or notes to a patient's GI doctor and vice versa are effective, especially if you are adding something new to a patient's treatment regimen." ▪