Feb. 20, 2015
Mayo Clinic has a distinguished history of investigating neural autoimmune disorders. An important aspect of this work concerns the occurrence of autonomic disease in an immune setting and the discovery that immunotherapy can be beneficial for patients with autonomic disease.
Although autonomic disease is typically associated with syncope, neuropathy and sweating problems, chronic gastrointestinal (GI) dysmotility also may be a component. Autoimmune GI dysmotility (AGID) is a newly described clinical entity that is a limited manifestation of autoimmune dysautonomia, and can occur as an idiopathic phenomenon. Signs and symptoms include early satiety, nausea, vomiting, bloating, diarrhea, constipation and involuntary weight loss. The onset may be subacute, and neurological manifestations may or may not be an accompaniment.
Colonic motility assessed
Colonic motility is assessed at 24 and 48 hours after ingestion of a tracer. Regions of interest are assigned numbers: 1, ascending colon; 2, transverse colon; 3, descending colon; 4, sigmoid colon/rectum; 5, stool. The estimated geometric center (Gc) is the average distance traveled by the ingested tracer. Normal Gc is 3.0 to 4.8 at 48 hours, indicating tracer should be in the descending colon or sigmoid colon/rectum. On the left, motility test in a patient with autoimmune GI dysmotility before intravenous immune globulin (IVIg) therapy shows Gc of 1.5 at 48 hours, indicating most tracer is in the proximal ascending colon. On the right, Gc is 3.8, in the normal range, at 48 hours after IVIg therapy.
In the September 2014 issue of Neurogastroenterology & Motility, Mayo Clinic researchers report the first objective evidence that immunotherapy may reverse autoimmune GI dysmotility. The study illustrates the importance of considering an autoimmune basis for acquired idiopathic GI motility disorders.
"The concept that you can have predominantly GI dysmotility — without necessarily having a lot of symptoms in other areas — and the conclusion that it is due to an immune mechanism affecting the nervous system of the gut is rather novel," says Sean J. Pittock, M.D., a consultant in the Department of Neurology at Mayo Clinic in Rochester, Minnesota, and founder of the autoimmune neurology clinic there. "But if the immune system can cause inflammation of the optic nerve, spinal cord or cerebral cortex, then why can't it cause a problem with the gut? After all, the gut contains 100 million neurons — more than the spinal cord or the peripheral nervous system."
AGID appears to be relatively uncommon; most GI symptoms are caused by other diseases or have a functional basis — for example, irritable bowel syndrome. The term "dysmotility" refers to abnormal movement of food, nutrients and waste through the digestive tract. With AGID, the presumption is that the nerves controlling the GI tract are being targeted by immune cells, resulting in altered neural function and thus, altered GI transit.
AGID can be disabling. "Patients who have these problems are miserable. They have no appetite. They have terrible abdominal pains and constipation. Often these patients undergo lots of diagnostic testing and multiple consultations," says Lawrence A. Szarka, M.D., a consultant in the Division of Gastroenterology and Hepatology at Mayo Clinic in Rochester, Minnesota.
The Mayo Clinic research was a retrospective case study of 23 patients seen at Mayo Clinic for suspected AGID, in whom an immunotherapy trial was undertaken. Seventeen of the patients improved after the six- to 12-week immunotherapy trial. Autoimmune serological evaluation revealed a neural-specific antibody in 12 of the 17 responders (71 percent). Symptomatic improvements were generally accompanied by objective evidence of improved GI motility and autonomic function on repeated scintigraphic, manometric and autonomic function tests.
"The observation that the immune system may be attacking parts of the nervous system and causing disorders that we might have explained away as a functional problem opens up possibilities for new, directed therapies to help the patient's GI symptoms," says Joseph A. Murray, M.D., a consultant in the Division of Gastroenterology and Hepatology at Mayo Clinic in Rochester, Minnesota.
"Treatment options for gastroparesis — a condition where the stomach does not empty food — are extremely limited, and the ones that exist merely facilitate gastric emptying or treat the symptoms. The idea that there may be a treatment that targets the underlying cause of gastroparesis is exciting," says Yuri A. Saito Loftus, M.D., a consultant in the Division of Gastroenterology and Hepatology at Mayo Clinic in Rochester, Minnesota.
AGID diagnostic panel
Mayo Clinic's standardized approach to autoimmune neurological conditions is based on three M's: determine the maximum reversibility of signs and symptoms, which also serves as a diagnostic test; maintain that maximal reversibility; and do so with minimal therapeutic dosage, thus reducing the likelihood of side effects.
Immunoglobulin G (IgG) autoantibodies
Immunoglobulin G (IgG) autoantibodies commonly identified in the Mayo Clinic neuroimmunology laboratory as part of the autoimmune GI evaluation. These antibodies bind to neural elements — myenteric ganglia (G), nerve fibers (NF) and nerve trunks (NT) in the enteric nervous system — in sections of mouse stomach (arrows). On the left, the characteristic staining pattern of an autoantibody, peripherin IgG, that was recently discovered at Mayo Clinic and is associated with GI dysmotility and autoimmune endocrinological disorders. On the right, the characteristic staining pattern of anti-neuronal nuclear antibody type 1 (ANNA-1, or anti-Hu antibody), which is associated with small cell lung cancer and GI dysmotility in 30 percent of affected patients.
To establish a diagnosis, patients are asked about a history of autoimmune disease — such as lupus or vitiligo — or cancer. They undergo neural antibody evaluation, which includes an autoimmune GI dysmotility panel that is the only one of its type in the U.S.
In addition, patients with suspected AGID have objective testing, particularly GI transit studies. Additional tests may include a gastroduodenal manometry or a colon motility study. Both tests measure intestinal contractions, and the pattern of contractions confirms or refutes a neurological basis for the slow GI transit.
When AGID is suspected, patients are given a 12-week "diagnostic" trial of intravenous immune globulin or methylprednisolone. A response to immunotherapy in the acute treatment phase of suspected AGID has diagnostic as well as therapeutic importance.
Although a lack of response doesn't imply a nonautoimmune etiology, clinical improvement obtained with immunotherapy is probably the single most important diagnostic test performed in the evaluation of a patient with a suspected AGID. It is imperative that baseline objective testing provide reference points for evaluating clinical improvement with immunotherapies. If symptoms and objective testing show improvement, the next step is to maintain that level of reversibility with the minimum effective dosage of maintenance oral immunosuppressants.
"Patients generally come in with subacute and often rapid onset of symptoms. The age range is usually in the mid-20s to 50s," Dr. Pittock says. "When we give them immunotherapy, the improvement can be dramatic. Patients can go from persistent nausea, vomiting and weight loss to feeling normal within a few weeks."
Some patients who test positive for antibodies don't respond to immunotherapy. Research continues in an effort to learn more about the association between autoimmune antibodies and GI dysmotility. One recent development is the discovery of an antibody that targets dipeptidyl-peptidase-like protein-6 (DPPX), a regulatory subunit of neuronal Kv4.2 potassium channels, which causes hypermotility resulting in diarrhea.
"Testing for this antibody may become part of our AGID diagnostic panel in the near future," Dr. Pittock says. "We are still very much learning how to approach these conditions."
Those efforts are facilitated by strong collaboration between clinician-researchers. "At Mayo, we work closely with our colleagues when diseases cross specialties," Dr. Murray says. "Patients get a single answer, not different answers from multiple specialists. As neurologists and gastroenterologists, we may come to the patient's problems from different perspectives. But ultimately we come to consensus on what is good for the whole patient."
For more information
Flanagan EP, et al. Immunotherapy trial as diagnostic test in evaluating patients with presumed autoimmune gastrointestinal dysmotility. Neurogastroenterology & Motility. 2014;26:1285.