Megan McClosky, DVM, DACVIM (SAIM), an internist and assistant professor at the University of Pennsylvania School of Veterinary Medicine, shared her knowledge and insights into irritable bowel disease (IBD) and its connection to small cell lymphoma (SCLSA ). 2022 American Association of Feline Practitioners Annual Conference in Pittsburgh, Pennsylvania.1 “IBD, small cell lymphoma – and possibly large cell lymphoma – represent a spectrum of diseases,” he explained to attendees. McClosky compared these diseases to moving targets that require veterinarians to change treatments as cats progress. This relative unpredictability makes ruling out certain, and sometimes more serious, gastrointestinal (GI) disorders more important than obtaining a biopsy in some cases, he added.
What is IBD?
IBD is a clinical definition that requires the presence of clinical signs and demonstration of inflammation in intestinal biopsies. Before the biopsy, McClosky explained that the inflammation that occurs is chronic enteropathy, which is further characterized by its response to treatment as diet responsive, antibiotic responsive, steroid responsive, and fiber responsive. “Ultimately, the underlying etiology of IBD is unknown in cats, but the disease may have some similarities to human IBD. We think it comes from a breakdown of tolerance within the gastrointestinal immune system to antigens in the diet, to antigens in bacteria, and possibly to self-antigen,” he explained. According to McClosky, biopsies from cats with IBD—or chronic enteropathy—usually reveal lymphoplasmacytic enteritis as the most common type of inflammation regardless of cause. However, lymphoplasmacytic enteritis is not limited to cats with IBD, McClosky clarified. It is also present in cats with hyperthyroidism, parasitic infections or asymptomatic felines. Less common types of inflammation may also occur, including eosinophilic, neutrophilic, granulomatous, or pyogranulomatous inflammation.
What is SCLSA?
SCLSA is a cancer that specifically affects the lymphocytes in the gastrointestinal tract. Although less aggressive than large or intermediate cell lymphoma, SCLSA has many clinical similarities to feline IBD. “The clinical signs may actually be identical,” he clarified. Hearing the term lymphoma, clients – especially those with loved ones with cancer – instinctively fear. “I like to talk to them about the differences between a small cell and a large cell,” he said. McClosky noted that small cell lymphoma will be less aggressive and cause diffuse thickening of the small bowel on ultrasound. Large cell lymphoma is more likely to cause mass-like lesions in the stomach, small intestine, and colon. “The median survival time for small cell lymphoma, if reached in studies, is usually 2 to 3 years. If we’re talking about cats diagnosed later in life, they may still die from something other than their cancer. Large cell lymphoma has a fairly poor prognosis, even with treatment. The median survival time is only about 6 to 8 months,” he said.
Diagnostic work
“The signs of gastrointestinal disease are pretty vague,” McClosky said. These signs include vomiting, diarrhea, weight loss, and changes in appetite. She told the audience that she reminds her students that cats with significant intestinal disease do not always present with vomiting and diarrhea. Weight loss in the face of a typical or increased appetite may be the only indication that something is wrong in the gastrointestinal tract. “Similar to treating pancreatitis, the key blood work is to rule out other causes of GI signs,” he explained. Feline patients with chronic enteropathy may have mild anemia or mild leukocytosis on a complete blood count (CBC), but it may be normal. Hypocholesterolemia is common in the chemistry panel, while panhypoproteinemia is possible but less common than in dogs. Another important part of the examination is stool testing to rule out intestinal parasites, nematodes and Giardia, especially in cats with weight loss and diarrhea. “Even if the stool is normal—because stool sensitivity is very poor if cats are not actively diarrheal—empirical deworming should also be done,” advises McClosky. A 2010 study published in the Journal of Veterinary Internal Medicine2 established a Feline Chronic Enteropathy Activity Index (FCEAI) to assess disease severity and response to treatment. The FCEAI scoring system includes scores for posture/activity, appetite, vomiting, stool consistency, stool frequency, and involuntary weight loss. Monitoring this value can be useful as an objective way to assess response to treatment, McClosky said. However, one of the index’s faults, he pointed out, is that it includes endoscopic biopsy scores, which would not be available when treating a patient without a biopsy diagnosis.
Is it possible to diagnose without a biopsy?
According to McClosky, GI biopsy remains the gold standard diagnosis for differentiating between IBD and SCLSA. While some clinical features are more consistent in one disease than another, there is too much overlap to be useful in individual patients. McClosky encouraged attendees to support biopsies for younger patients with refractory disease, patients who may be intolerant to oral medications, those with comorbidities that require dietary therapy, and patients who may respond poorly to steroids. However, forgoing a biopsy does not mean that treatment is impossible. To hit the moving target, special care and attention must be given.
Important differences to exclude
“If a sick cat with a GI looks like a sick cat with a GI and we think we’re not going to be able to biopsy, there are other things to think about that might get worse with treatment,” McClosky explained. Infectious diseases causing gastrointestinal signs are more likely to occur in younger patients or those with a compatible travel history. “Many infectious conditions can be made much worse by starting steroids, so it’s important to rule them out. and in some cases, more important than a gastrointestinal biopsy,” he warned. “If you know you’re not going to have a biopsy, some things to consider would be infectious disease testing, fungal testing, stool polymerase chain reaction (PCR) panels, stool cultures, and abdominal imaging,” she encouraged. Infectious diseases to consider include Giardia, clostridial infections, invasive mycosis, histoplasmosis, and salmonellosis. Further diagnostics should include a malabsorption/dyspepsis panel, pancreatic lipase immunoreactivity, and trypsin-like immunoreactivity. Finally, abdominal imaging is recommended to rule out mass-like lesions in the gastrointestinal tract or other organs and may even lead to a more positive finding. For example, ultrasound-confirmed polyps may cause vomiting due to partial obstruction and changes in appetite, but are often benign and can be removed.
Management
Pharmacologic interventions for IBD and SCLSA are nearly identical, especially if the IBD is refractory to nutritional management, McClosky said. Patients who can maintain a good appetite, have no or minimal weight loss, and minimal vomiting or diarrhea should undergo empiric trials of a novel protein or hydrolyzed protein diet and/or a trial of antibiotics with metronidazole or tylosin. Typically, it takes 4 to 8 weeks to see a response. If a patient is incapacitated, losing weight rapidly, or has severe clinical signs, faster-acting therapy should be prescribed. Once GI tract variations have been ruled out, a trial of steroids for chronic enteropathy can be initiated. If there is a partial response to steroids, the addition of chlorambucil can achieve complete disease control. The initial treatments for SCLSA are prednisolone and chlorambucil, so the treatment ends up being the same, he pointed out. The goal in any case is to reduce the clinical signs of the disease, but it is unlikely to eliminate them. “These are diseases that are managed, not cured,” McClosky concluded. bibliographical references
