Intestinal Leiomyositis: A Cause of Chronic Intestinal Pseudo‐Obstruction in 6 Dogs

Abstract

BackgroundIntestinal leiomyositis is a suspected autoimmune disorder affecting the muscularis propria layer of the gastrointestinal tract and is a cause of chronic intestinal pseudo‐obstruction in humans and animals.ObjectiveTo characterize the clinical presentation, histopathologic features, and outcome of dogs with intestinal leiomyositis in an effort to optimize treatment and prognosis.AnimalsSix client‐owned dogs.MethodsRetrospective case series. Medical records were reviewed to describe signalment, clinicopathologic and imaging findings, histopathologic diagnoses, treatment, and outcome. All biopsy specimens were reviewed by a board‐certified pathologist.ResultsMedian age of dogs was 5.4 years (range, 15 months–9 years). Consistent clinical signs included vomiting (6/6), regurgitation (2/6), and small bowel diarrhea (3/6). Median duration of clinical signs before presentation was 13 days (range, 5–150 days). Diagnostic imaging showed marked gastric distension with dilated small intestines in 4/6 dogs. Full‐thickness intestinal biopsies were obtained in all dogs by laparotomy. Histopathology of the stomach and intestines disclosed mononuclear inflammation, myofiber degeneration and necrosis, and fibrosis centered within the region of myofiber loss in the intestinal muscularis propria. All dogs received various combinations of immunomodulatory and prokinetic treatment, antimicrobial agents, antiemetics, and IV fluids, but none of the dogs showed a clinically relevant improvement with treatment. Median survival was 19 days after diagnosis (range, 3–270 days).Conclusions and Clinical ImportanceIntestinal leiomyositis is a cause of intestinal pseudo‐obstruction and must be diagnosed by full‐thickness intestinal biopsy. This disease should be considered in dogs with acute and chronic vomiting, regurgitation, and small bowel diarrhea.

Proceedings of the 2018 National Toxicology Program Satellite Symposium

“…The mononuclear inflammatory cell infiltrate was primarily composed of CD3 positive T lymphocytes and Iba1 positive histiocytes with fewer CD20 positive B lymphocytes (Figure 4EG). These findings are similar to human and canine cases, which are characterized by a predominance of T lymphocytes (Ruuska et al 2002; Zacuto et al 2016). In addition, alpha smooth muscle actin immunohistochemistry highlighted the loss of myofibers among the inflammatory cell infiltrate (Figure 4H).…”

“…In dogs, the clinical features of intestinal leiomyositis include vomiting, regurgitation, diarrhea, anorexia, and weight loss (Zacuto et al 2016). The most common clinical pathology findings include hypoalbuminemia, hypocholesterolemia, and neutrophilia (Zacuto et al 2016). Histopathologically, there is infiltration of the tunica muscularis by mononuclear cells along with myofiber degeneration and variable fibrosis (Zacuto et al 2016).…”

“…The most common clinical pathology findings include hypoalbuminemia, hypocholesterolemia, and neutrophilia (Zacuto et al 2016). Histopathologically, there is infiltration of the tunica muscularis by mononuclear cells along with myofiber degeneration and variable fibrosis (Zacuto et al 2016). The small intestine is most commonly affected; however, involvement of the stomach and colon is also reported (Couraud et al 2006; Johnson et al 2007; Zacuto et al 2016).…”

“…Histopathologically, there is infiltration of the tunica muscularis by mononuclear cells along with myofiber degeneration and variable fibrosis (Zacuto et al 2016). The small intestine is most commonly affected; however, involvement of the stomach and colon is also reported (Couraud et al 2006; Johnson et al 2007; Zacuto et al 2016). In affected patients, similar lesions have also been described at distant sites, such as the urinary bladder and smooth muscle of the eyelid (Johnson et al 2007; Zacuto et al 2016).…”

“…Common comorbidities include small intestinal bacterial overgrowth (SIBO) and aspiration pneumonia secondary to vomiting and regurgitation. The pathogenesis of intestinal leiomyositis is unknown, although autoimmunity is suspected (Ruuska et al 2002; Zacuto et al 2016).…”